How can endemic proboscideans help us understand the “island rule”? A case study of Mediterranean islands

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How can endemic proboscideans help us understand the ‘‘island rule’’? A case study of Mediterranean islands Maria Rita Palombo Dipartimento di Scienze della Terra, Universita` degli Studi di Roma ‘‘La Sapienza’’, and CNR—Istituto di Geologia, Ambientale e Geoingegneria. Piazzale Aldo Moro, 5, 00185 Rome, Italy Available online 22 May 2007

Abstract Several hypotheses have been advanced to explain size-change processes in terrestrial vertebrates on islands and in island-like ecosystems. Extinct endemic insular proboscideans are especially appropriate subjects for investigating this issue, given the frequency with which proboscideans colonised islands, and the multiple patterns in size reduction experienced by endemic taxa on different islands, as well as on a single one. To verify whether evolutionary trends in elephants from Mediterranean islands might result from predictable responses to different niche availability and selection regimes in insular and mainland environments, the body-mass (considered as the best proxy of body-size) trends in endemic species and the body-mass structure of unbalanced insular have been compared to those of coeval balanced mainland mammalian complexes. Evolutionary patterns shown by endemic elephants suggest that, in isolated environments, the body-size of small and large non-carnivorous mammals depends on parsimonious optimisation of their life-history traits (metabolic rate, age at maturation and gestation time, trophic level, home range size, population density, etc.). Accordingly, it is rational to hypothesise that insular mammals change their size, in accordance with their initial bau-plan, depending on the most appropriate ‘‘empty’’ niche available on the island and the size of some vacant groups of competitor species, perhaps developing novel ecological strategies. r 2006 Elsevier Ltd and INQUA. All rights reserved.

1. Introduction Terrestrial mammalian communities populating geographically and/or ecologically isolated districts generally include a limited number of species, are less diversified and compositionally unbalanced as compared to communities of similar but non-isolated biotopes. Hence, the pathways of island colonisation and the evolutionary changes that endemic settlers undergo in response to the special characteristics of island environments (above all variation in body-size as a function of island area and isolation, or other interacting factors such as ecological release, shortage of resources, dispersability etc.) have greatly interested evolutionary biologists, ecologists and biogeographers (see e.g. Foster, 1964; Carlquist, 1974; Hooijer, 1976; Sondaar, 1977; Heaney, 1978; Marshall and Corruccini, 1978; Azzaroli, 1982; Reyment, 1983; Lomolino, 1985; Malatesta, 1986; Roth, 1992; Adler and Levins, 1994; Brown and Lomolino, 1998; Grant, 1998; Whittaker, E-mail address: [email protected]

1998; Drake et al., 2002; McNab, 2002; Filin and Ziv, 2004; Gould and MacFadden, 2004; Carvajal and Alder, 2005; Woofit and Bromham, 2005; Lomolino et al., 2006; Meiri et al., 2006). Immigration, extinction and evolution, varying according to the area and isolation of the island, as well as differences in resource requirements and immigration abilities among species groups, have been regarded as the factors that have the greatest influence on the structure and dynamics of insular communities. Since the publication of MacArthur and Wilson’s basic paper (MacArthur and Wilson, 1967), the equilibrium theory of island biogeography has been extensively pondered, and alternative models have been proposed, attempting to provide an explanation for a variety of patterns, such as species/area and species/isolation relationships, distribution of individual species, interspecific interactions, potential feedback processes and assembly patterns of insular communities, which may or may not lead to equilibrium (cf. e.g. Whitehead and Jones, 1969; Brown, 1971; Heaney, 1986, 2000; Lomolino, 1986, 2000a, b, 2005; Hanski, 1992;

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Dayan and Simberloff, 1998; Grant, 1998; Hoekstra and Fagan, 1998; Morrison, 1998; Whittaker, 1998, 2006; Millien-Parra and Jaeger, 1999; Fox and Fox, 2000; Johnson et al., 2000; Morand, 2000; Ward and Thornton, 2000; Gaston et al., 2001; Lomolino and Weiser, 2001; Filin and Ziv, 2004; Badano et al., 2005; Lomolino et al., 2006 and references therein). The speciation of endemic mammals in unbalanced PlioPleistocene faunas on islands in many biogeographic provinces (Mediterranean, Sunda Archipelago, South China Sea, and Eastern Pacific Ocean) surely represents a special sphere in the study of evolutionary processes in isolated areas, and, in particular, for testing hypotheses that have been advanced to explain size-change processes in terrestrial vertebrates on islands and in island-like ecosystems. 1.1. Why endemic elephants from Mediterranean islands? Proboscideans, encompassing endemic taxa whose bodysize reduction is more extreme than that observed for any other insular dwarfs, are especially appropriate subjects for analysing bodysize changes in isolated environments, due to the frequency with which they have colonised islands, giving rise to several endemic taxa with more or less reduced body-size in comparison with their own continental ancestors: elephantoid endemic species (Sinomastodon and Stegodon) were found in the Pleistocene deposits from Java, Sulawasi and Flores; palaeoloxodontine elephants were the most characteristic and common taxa in Pleistocene endemic unbalanced or impoverished mammal faunas from the Western and Eastern Mediterranean islands (Sicily, Malta and the Aegean Islands, Crete, the Cyclades, Dodecanese Islands and Cyprus); and dwarfed Mammuthus species have been recorded in the Pleistocene deposits of Sardinia and Crete, as well as on Santa rosae super-island (California) (Palombo, 2004a, b and references therein). Compared to their mainland forebears, endemic proboscideans were characterised by similar evolutionary patterns permitting the appearance of homoplastic features, more marked as size became smaller: brain volume increased proportionally as compared to body-size; cranial bones, notably the frontal and parietal ones, reduced their own pneumanisation; in the molars, the number of laminae decreased relative to the size of the tooth, whereas the enamel became thicker and less pleated; in limb bones, the whole structure, and in particular the morphology of articular joints, testified to a reduction in graviportal posture. Moreover, greater morphological variability seems to have characterised dwarfed elephants, presumably as a consequence, at least in part, of an increase in morphological and dimensional sexual dimorphism (e.g. Theodorou, 1983; Lister, 1996; Davies and Lister, 2001; Roth, 2001; Palombo, 2004b, 2005b, and references therein). Particularly during the Pleistocene, elephants on Mediterranean islands (Fig. 1) underwent size reduction

to an extreme degree. Therefore, dwarfed elephants may be considered one of the most prominent examples of Foster’s island rule (Foster, 1964; Roth, 2001; Palombo, 2004b). In addition, endemic taxa originating from successive migrations by the same continental taxon show — even on the same island — different sizes, contradicting any relationship among the magnitude of body-size shifts towards dwarfism and island surface (Palombo, 2004b and references therein). This fact makes it possible to compare different patterns of speciation and body-size modification, assessing the influence of various factors such as the extension of the island, its distance from the mainland, the nature and extension of barrier(s), the duration of isolation, the physiographic, climatic and microclimatic characteristics of the insular district, its vegetation cover, faunal turnover, survival of pre-existing species, shift in diversity and changes in communities’ structure due to the nature of the pioneering species and all other factors affecting type and availability of ‘‘empty’’ niches. The aim is to use endemic elephants from Mediterranean islands to verify whether evolutionary trends in insular taxa might result from predictable responses to differences in competition and niche availability in insular and mainland environments. In this regard, the aspects meriting major consideration are body-size trends in endemic species and the body-size structure of unbalanced insular mammalian complexes as compared to coeval balanced mainland ones. 2. The ‘‘island rule’’: theoretical framework Since the early 20th century, it has been known that almost all characteristics of organisms vary predictably with body-size, given that body-size is a major factor constraining the structure and functioning of organisms. During the last two decades, studies on body-size variation in insular vertebrates, and in vertebrates isolated and persisting in fragmented continental environments, have multiplied. Furthermore, several recent analyses of bodysize trends displayed by insular taxa have been performed to test the validity and explain the mechanisms of Foster’s so-called ‘‘island rule’’ (Foster, 1964; Van Valen, 1965, 1973), which postulates gigantism in smaller and dwarfism in larger species of insular mammals. 2.1. Body-size patterns in insular vertebrates Foster (1964) documented insular size trends in mammal groups and concluded that insular rodents tend to increase in size, whereas artiodactyls (even-toed ungulates, especially deer), carnivores and lagomorphs (rabbits and hares) tend to decrease in size, with marsupials and insectivores showing no consistent trends. Lomolino (1985) confirmed the ‘‘island rule’’, reinterpreting the pattern as a graded trend from dwarfism in larger mammalian species to gigantism in small mammals, as well as in stringiform birds and some reptiles. Insular size trends have been extensively discussed (e.g. Thaler, 1973; Sondaar, 1977;

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Fig. 1. Endemic elephants on Mediterranean islands.

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Case, 1978; Heaney, 1978; Alcover et al., 1981; Azzaroli, 1982; Lawlor, 1982; Reyment, 1983; Lomolino, 1985, 2005; Malatesta, 1986; Diamond, 1987; Damuth, 1993; Brown and Lomolino, 1998; Grant, 1998; Whittaker, 1998; Michaux et al., 2002; Schmidt and Jensen, 2003; Lomolino et al., 2006; Meiri et al., 2006) and described in detail for terrestrial extant and extinct vertebrates: reptiles (e.g. Mertens, 1934; Case and Bolger, 1991; Jianu and Weishampel, 1999; Boback, 2003; Keogh et al., 2005; Wikelski, 2005; Jessop et al., 2006), including dinosaurs (e.g. Jianu and Weishampel, 1999; Sander et al., 2006); birds (e.g. Case et al., 1982; Clegg and Owens, 2002; Robinson-Wolrath and Owens, 2003); small mammals (e.g. Freudenthal, 1972; Melton, 1982; Angerbjo¨rn, 1986; Smith, 1992; Adler and Levins, 1994; Reumer, 1996; Pergams and Ashley, 2001; Millien, 2004; Millien and Damuth, 2004; White and Searle, 2006), including bats (e.g. Krzanowski, 1967); and large mammals (e.g. inter alios Vaufrey, 1929; Stock, 1935; Hooijer, 1951, 1976; Roth, 1990, 2001; de Vos, 1996, 2000; Lister, 1996; Spaan, 1996; Anderson and Handley, 2002; Endo et al., 2002; Poulakakis et al., 2002; Bover and Alcover, 2005; Croft et al., 2006) including carnivores (e.g. Gordon, 1986; Hoekstra and Fagan, 1998; Meiri et al., 2005a, b, 2006), and humans (Brown et al., 2004; Morwood et al., 2005), as well as for invertebrates (e.g. Darlington, 1943; Palmer, 2002; Badano et al., 2005; Gentile and Argano, 2005). Furthermore, similar trends have been described for plants, since small herbaceous plants take on the form of trees (‘‘insular woodiness’’ sensu Carlquist, 1974) (e.g. Carlquist, 1980; Shmida and Werger, 1992; Givinish, 1998; Panero et al., 1999; Bernardello et al., 2001). Nevertheless, some examples of large mammals becoming even larger on islands are reported — for example, the Pleistocene deer from Crete ascribed to ‘‘Cervus’’ major and, perhaps, ‘‘Cervus’’ dorothensis (Capasso Barbato, 1990; ¼ Candiacervus sp. VI and Candiacervus sp. VII in de Vos, 1996, 2000 and previous papers) or the Kodiak bear (Gordon, 1986), whereas small mammals becoming even smaller (e.g. Ganem et al., 1995; Nor, 1996; Mills et al., 2004) or remaining the same size are also recorded (e.g. the gliridae Leihia cartei from Malta and Sicily, Zammit Maempel and de Bruijn, 1982). Moreover, Sondaar and Boekschotten (1967) claimed that insectivores do not generally change their size on islands (due to their reduced ‘‘plasticity’’), basing their observation mainly on shrews from Crete. Actually, small Insectivora frequently increase their size on islands (see e.g. Reumer, 1980; Reumer and Oberli, 1988; Fons et al., 1997; Fanfani, 2000 and references therein) and a very large hedgehog, Deinogalerix koenigsvaldi, is recorded in the late Neogene Gargano paleoarchipelagos (Italy) (Freudenthal, 1972). On the other hand, if reptiles display many remarkable examples of insular giants, insular snakes are generally smaller than their mainland relatives (Case, 1978), and Caribbean Anolis show great variation, possibly due to niche partitioning among co-occurring species

(Schoener, 1969). Thus, even if the tendency for island populations to differ in body-size from their mainland relatives has been well documented, changes in the size of vertebrates once segregated in isolated geographic areas such as islands, and notably dwarfism in large mammals, is a debatable subject, with the mechanisms for these size changes remaining speculative. 2.2. Previous explanations In the past few decades, several authors have emphasised the role played by different factors in explaining evolutionary patterns in isolated areas, especially changes in body-size. Even if dispersal to islands and the area of the insular surface are particularly taken into consideration, three principal potential causal explanations have generally been invoked to explain insular size shifts in vertebrates: the release of predation pressure (especially that from large carnivores, often absent from oceanic and oceanic-like islands, (sensu Alcover et al., 1998), the paucity of interspecific competition and predation, and the effects of limited resources. As large terrestrial predators have not been recorded in unbalanced insular faunas, the lack of their selection pressure was considered one of the most important factors explaining insular dwarfing and gigantism (e.g. Thaler, 1973; Sondaar, 1977; Lomolino, 1985). Other authors have attributed a major role to the host-island surface (e.g. Lomolino, 2000a, b; Burness et al., 2001; Badano et al., 2005), coupled with other factors such as competition and trophic resources (e.g. Heaney, 1978), some behavioural features such as territoriality (Case, 1978; Case et al., 1982), trophic requirements and metabolic rate (e.g. Burness et al., 2001 and references therein) or feeding specialisation (Lawlor, 1982; Scott et al., 2003). For instance, the niche expansion hypothesis assumes small mammals can increase their size on small islands due to the poor diversity of interspecific competitors (Heaney, 1978). Moreover, increased niche breadth should favour overspecialisation as regards particular food resources (however, cfr. Palkovacs, 2003 and references therein). Other authors have pointed to the impact of genetic segregation and endogamy (Malatesta, 1986), to the ‘‘peculiarity’’ of pioneer species, such as ‘‘plasticity’’ and reproduction rate (Sondaar and Boekschotten, 1967), or to ‘‘environmental factors,’’ such as area reduction, population density, overgrazing (Theodorou, 1988), as well as overcrowding (Roth, 1990). Accordingly, a multitude of hypotheses (genetic pool impoverishment, endogamy, heterochrony, decrease in diversity; modification of inter- and intra-specific relationships, hormonal alterations, shortage and starvation, population density, nature of available niches, and so on) have been formulated to explain such insular size trends (cfr. inter alios Hooijer, 1949, 1951; Foster, 1964; MacArthur and Wilson, 1967; Diamond and May, 1976; Sondaar, 1977; Case, 1978; Heaney, 1978; Alcover et al., 1981; Azzaroli, 1982; Lomolino, 1985; Malatesta,

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1986; Caloi and Palombo, 1989; Roth, 1992; Wilson, 1992; Sondaar et al., 1996; de Vos, 2000; Burness et al., 2001; Poulakakis et al., 2002 and references therein). More recently, Palkovacs (2003) hypothesised that size trends in insular species do not depend on particular selective pressures but on general life history responses to environmental changes commonly encountered on islands. Indeed, the main selective forces invoked by previous hypotheses, such as decreased resource availability and reduced predation pressure, can work to produce body-size changes via the evolution of life-history traits. Filin and Ziv (2004) suggested a new theory connecting body-size and dispersability with isolation and island area. These authors claimed that direction and rate plus magnitude of body-mass changes respectively depend on dispersability and island area. On the other hand, Palombo (2004b), with regard to herbivores, stressed the importance of intra-guild competition, suggesting that within a given trophic level, body size depends principally on the number and nature of suitable vacant niches in a given insular area. Indeed, it might be supposed that the smaller the individuals in a given population, the less food is required within a trophic level, and hence the larger the number of individuals making up the population and the greater the possible genetic exchange, avoiding, for instance, the risk of extinction. Accordingly, due to the reduction in intraguild competition in insular environments, large herbivores would reach a body size similar to the body size of herbivores that on mainland occupy the niches that are unoccupied on the island. Furthermore, Palombo (2005a) suggested that ‘‘in isolated environments, the body size of small/large [non-carnivorous] mammals relies on parsimonious optimisation of their life-history traits (metabolic rate, age at maturation and gestation time, trophic level, home-range size, population density, etc.) in accordance with their bau-plan and the most appropriate niche available on the island’’. Lomolino (2005) also claimed that ‘‘the island rule is an emergent pattern resulting from a combination of selective forces whose importance and influence on insular populations vary in a predictable manner along a gradient from relatively small to large species’’, and ‘‘as a result, body size of insular species tends to converge on a size that is optimal, or fundamental, for a particular bau plan and ecological strategy’’. Actually, body-size trends of mammals in isolated environments result from a combination of selective forces whose importance seems to fluctuate along a gradient from small to large species; moreover underlying mechanisms might differ in different lineages and at different trophic levels. For instance, Meiri et al. (2006), on the basis of two large data sets of insular and mainland extant carnivores, argued that the ‘‘island rule’’ is not a general pattern for all mammals. The aim of this study is to verify whether the patterns shown by endemic elephants from Mediterranean islands do or do not contribute to explaining the ‘‘island rule,’’ and its exception, in a rather general way, at least as far as herbivores is concerned.

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3. Material and methods 3.1. Source of data The most interesting faunas are those recorded on a single island at different times, including endemic elephants, whose size varies according to the age of the deposit and the type of fauna accompanying it. Of particular interest are those faunas encompassing endemic elephants, originating from a common ancestor that colonised an island in more than one migration wave. Accordingly, taxonomical lists of Pleistocene local faunal assemblages (LFAs) from Sicily, Sardinia and Crete have been critically revised. Since for these purposes the significance of results is largely dependent on how faithfully the samples (species occurring in the same stratigraphic horizon) were analysed reflect original community composition, only biochronologically controlled LFAs were selected for analysis. LFAs coherent from a biochronological and ecological point of view were then grouped into faunal complexes (FCs) (sensu Palombo, 2005b), so as to facilitate comparison with continental faunas from the same temporal intervals. 3.2. Methods Which parameter would be the most appropriate to analyse body-size changes in insular fossil mammals? Measurements of crania, teeth or limb bones have been considered for decades the only size indices available for fossil specimens. On the other hand, body-mass, the most useful indicator of species adaptations in fossil species, considered a proxy of body size, according to Gingerich et al. (1982), can be regarded as the ‘‘best’’ index. Estimating the body-mass of fossil mammals is not easy; and several methods have been proposed. For that reason, the body-mass of each taxon is estaimated using different allometric relationships and choosing the most appropriate method tested as the most adequate for each taxon: Delson et al. (2000) for primates; Van Valkenburgh (1988, 1990) for large carnivores; Legendre (1986) for small mammals, and small carnivores; Palmqvist et al. (2002) and Legendre and Roth (1988) for medium-sized carnivores; Alberdi et al. (1995) for Equidae; Scott (1990) and Anderson et al. (1985) for large ruminants; Giovinazzo et al. (2006), Palombo and Giovinazzo (in preparation) for small and medium-sized artiodactyls. As regards Proboscidea, various equations have been proposed (Roth, 1990; Christiansen, 2004; Palombo and Giovinazzo, 2005). Here, femur length is used, due to the major frequency of this bone in fossil records. The values obtained for each species in each insular and mainland FCs were utilised to described body-mass structure of selected insular and mainland FCs. The rank-ordered distribution of body-mass in mammalian complexes has been assessed as in Valverde (1964), separating carnivores from non-carnivorous species, but using the logarithm of body-mass as adopted in Legendre’s

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cenograms to describe the weight distribution of nonvolant, non-carnivorous species in a mammalian community (Legendre, 1986, 1989). A cenogram is constructed by

plotting the logarithm (herein calculated as log10) of mean body-mass obtained for each species on the Y-axis against ordination by decreasing size on the X-axis (Figs. 2–5).

8 E. falconeri FC - Fontana Ranuccio FU

Proboscideans

7

F. R a n u c c i o FU

Perissodactyls Artiodactyls

6

Primates Rodents

5

Insectivores

4

Lagomorphs Carnivores

3

E. falconeri FC non Carnivora E. falconeri FC. Carnivora

2 1 0 0

10

20

30

40

50

60

70

8 E. manidriensis FC - Torre in Pietra FU

Proboscideans

7

T.

Perissodactyls P i e t r a

Artiodactyls

6

Primates Rodents

5

Insectivores

4

Lagomorphs

FU

Carnivores

3

E. mnaidriensis FC non Carnivora E. mnaidriensis FC Carnivora

2 1 0 0

10

20

30

40

50

60

70

8 San Teodoro cave, Pianetti FC - Last Interglacial 7 Proboscideans

6 Perissodacyls

5

Artiodactyls Carnivores

4

Rodents

3

Insettivorer

L a s t

I n t e r g l a c i a l

2

Lagomorphes

1

SanTeodoro cave - Pianetti FC non Carnivora SanTeodoro cave - Pianetti FC Carnivora

0 0

10

20

30

40

50

60

70

Fig. 2. Comparison among the body-mass structure of faunal complexes from Sicily and coeval mammalian complexes from the Italian peninsula. Cenogram construction: a cenogram is a graphic representation of the rank-size distribution (logarithm of body-mass plotted against taxa assessed according to their decreasing body-mass) of non-volant, non-carnivore mammal species within an ecologically cohesive fauna (see Legendre, 1986, 1989). Here the rank-ordered distribution of body-mass has been assessed, separating carnivores from non-carnivorous species, as in Valverde (1964). Each point corresponds to the mean body weight (on the y-axis) of a mammalian species, ordered by decreasing size (on the y-axis). The grey band indicates the critical interval from 500 to 8000 g.

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7

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Sicily

6 5 4 3 2 1 0

E. falconeri FC

E. mnaidriensis FC

Gr. S. Teodoro-Pianetti FC

Castello FC

Fig. 3. Comparison among body-mass structure of the Pleistocene mammalian complexes from Sicily. For each faunal complex, each point corresponds to the mean body weight (on the y-axis) of a mammalian species, ordered by decreasing size (on the y-axis). The grey band indicates the critical interval from 500 to 8000 g. Carnivora ¼ small symbols.

7

Sardinia

6 5 4 3 2 1 0

Orosei faunal sub-complex

Dragonara faunal sub-complex

Fig. 4. Comparison among body-mass structure of the Middle and Late Pleistocene mammalian subcomplexes from Sardinia, belonging to Microtus (Tyrrhenicola) faunal complex (sensu Palombo, 2006). For each faunal complex, each point corresponds to the mean body weight (on the y-axis) of a mammalian species, ordered by decreasing size (on the y-axis). The grey band indicates the critical interval from 500 to 8000 g. Carnivora ¼ small symbols.

7

Crete

6 5 4 3 2 K. aff K. kiridus sub-FC 1 0

Kritimys kiridus sub-FC Kritimys catreus sub-FC Mus bateae sub-FC Mus minotaurus sub-FC

Fig. 5. Comparison among body-mass structure of the Pleistocene faunal subcomplexes from Crete. For each faunal complex, each point corresponds to the mean body weight (on the y-axis) of a mammalian species, ordered by decreasing size (on the y-axis). The grey band indicates the critical interval from 500 to 8000 g. Carnivora ¼ small symbols.

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4. Body-size structure in the Pleistocene mammalian faunal complexes on the Mediterranean islands In the following sections, only the main FCS of Mediterranean islands including endemic elephants are briefly described. According to this analysis, the body-mass structure obtained for each FC is discussed, and compared with the structure of coeval mainland mammalian FCs. 4.1. Sicily On the basis of the rich fossil record and correlation of vertebrate-bearing deposits with marine deposits, Late

Pliocene(?) — Pleistocene local faunal assemblages (LFAs) from Sicily can be arranged into five Faunal Complexes (FCs) (Table 1) (Bonfiglio et al., 2002, and references therein). Endemic elephants, Elephas (Palaeoloxodon) falconeri and Elephas (Palaeoloxodon) mnaidriensis, respectively, occurred in early Middle Pleistocene (E. falconeri FC) and late Middle-early Late Pleistocene LFAs (E. mnaidriensis and San Teodoro cavePianetti CFs). Such faunal complexes show, on average, a progressive increase in diversity and decrease in ‘‘endemic signatures’’. The occurrence of at least two endemic elephants of different size (see Palombo, 2004b for a discussion) demonstrates that the mainland Elephas (Palaeoloxodon) antiquus colonised Sicily during more than one migratory wave.

Table 1 Chronological distribution of the Pleistocene mammalian taxa from Sicily Selected taxa

Faunal complexes “Monte Pellegrino”

“Elephas falconeri”

“Elephas “S. Teodoro mnaidriensis” cave - Pianetti”

Pellegrinia panormensis

?

Erinaceus europaeus Erinaceus aff. E.europaeus Asoriculus burgioi Crocidura esuae Crocidura aff. C. esuae Crocidura cf. C. sicula Leithia sp. Leithia cartei Leithia melitensis Leithia cf. L. melitensis Maltamys cf. M. gollcheri Maltamys gollcheri Maltamys cf. M. wiendincitensis Microtus (Terricola) ex. gr. M. savii Apodemus maximus Apodemus cf. A. silvaticus Hypolagus sp. Lepus europaeus Nesolutra trinacriae Pannonictis arzilla Ursus cf. U. arctos Crocuta crocuta cf. C. c. spelaea Vulpes sp. Vulpes vulpes Canis lupus Panthera spelaea Elephas (Palaeoloxodon) falconeri Elephas (Palaeoloxodon) mnaidriensis Equus ferus Equus hydruntinus Sus scrofa Hippopotamus pentlandi Cervus elaphus Cervus elaphus siciliae Dama carburangelensis Bos primigenius Bos primigenius siciliae Bison priscus siciliae

?

“Castello”

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4.1.1. E. falconeri FC The first migration possibly took place at the transition from the Early Pleistocene to Middle Pleistocene, or slightly later, when, as a result of early Middle Pleistocene cold phases (MIS 24-22-?20), sea level dropped and the distance between the island and mainland coastlines was reduced. Peopling occurred by crossing a severe barrier, which prevented any other large mammal from reaching the island. E. falconeri, originating from this colonisation phase and a subsequent dwarfing process, is the smallest endemic elephant found to date on Mediterranean islands: the adult male would have a maximal withers height of about 120 cm and a body-mass of about 170 kg. Moreover, E. falconeri is characterised by precocious stunting of ontogenetic growth, as confirmed by skull features, tusk structure and the proportions between the cranium, axial skeleton and limbs (Palombo, 2001, 2003). E. falconeri FC is characterised by a very poorly diversified and strongly unbalanced mammalian fauna (Table 1), including small mammals which evolved from species already present in the Early Pleistocene Monte Pellegrino FC (Leithia cartei, Leithia melitensis and Maltamys gollcheri), as well as newcomers such as the shrew Crocidura esuae and the otter Nesolutra trinacriae. The presence of a small fox, Vulpes sp., remains to be confirmed. The E. falconeri FC also includes a rich herpeto- and avifauna. Paleontological and geological evidence denotes the occurrence of an insular system made up of geographically isolated islands (the Hyblean Plateau, Peloritani, Nebrodi mountains), with very difficult, sporadic connections with the mainland (Bonfiglio et al., 2002). The body-mass structure of this FC and its comparison with the coeval FC of the Italian peninsula (Fontana Ranuccio faunal unit, FU, Palombo, 2005b) (Fig. 2) clearly denotes the availability for insular elephants of niches that on the mainland are typical of medium-sized and large herbivores such as perissodactyls and artiodactyls. Conversely, the niche of large continent species, such as leporids, became available for Sicilian small mammals. For instance, among endemic small mammals, the body size of the shrew is conspicuously larger than its mainland relative. In addition, it is worth noting that the body size of Sicilian endemic small mammals scales with a roughly constant ratio that approximates a size ratio of 1.33E2. This value matches the ratio considered by Hutchinson (1959) as permitting species to avoid competition, and partition resources with a minimum overlap (however, cfr. Roth, 1981; Maiorana, 1990; Dayan and Simberloff, 1996). On the other hand, E. falconeri shifts toward occupancy of the size (and niche) of the vacant mixed-feeder cervid species, due the lack of any intra-guild competition. This size reduction seems to have involved development toward a modified bau-plan (Palombo, 2003). Moreover, the lack of predators and the absence of selective predation pressure are consistent with the hypothesis that in the absence of

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threatening predators and intra-guild competition, large mammals could safely reduce their own body-mass to an extreme degree. 4.1.2. E. mnaidriensis FC A second set of migratory waves probably took place during the sea level drop related to the stadial oscillations in the late Middle Pleistocene (MIS 10, 8 and 6). These phases involved several mammalian taxa, including some with limited swimming abilities, such as carnivores and bovids. The new colonisation gave rise to the E. mnaidriensis FC, impoverished, but quite diversified and balanced from a trophic point of view. Specimens ascribed to E. mnaidriensis have been retrieved from several localities (see for instance Burgio, 1997; Bonfiglio et al., 2002 and references therein). In these LFAs, elephants were frequently associated with endemic, but not really dwarfed, taxa such as Hippopotamus pentlandi, Cervus elaphus siciliae and Dama carburangelensis, as well as with continental taxa (such as large carnivores and suids) (Table 1). The taxonomical composition and moderate endemisation’s degree suggest that temporary connections with southern Italy probably occurred. Nonetheless, it seems that a filtering barrier (ecological?) affected dispersal, preventing any small mammal from reaching Sicily, with the exception of Erinaceus europeus. The richest assemblage known to date comes from the early Late Pleistocene deposits in the Puntali Cave (Carini, Palermo); it was described by Pohlig (1893), who illustrated, under the name of ‘‘Elephas (antiquus) Melitae’’ Falconer, six skulls, smaller but very similar to those of E. antiquus. On the basis of the largest specimens found in LFAs belonging to E. mnaidriensis FC, E. mnaidriensis would have a withers height of about 2 m and a body weight of about 2500 kg. Actually, some larger specimens in some case reaching the minimum size of the continental E. antiquus from the Italian peninsula (see inter alios Osborn, 1942; Trevisan, 1949; Maccagno, 1962; Ferretti, 1998; Palombo unpublished data) have been recorded in the Contrada Fusco LFA, where the medium-sized Elephas mnaidriensis is abundant (Basile and Chilardi, 1996; Chilardi, 2001). Chilardi (2001) noted that among elephant specimens from Contrada Fusco, ‘‘large-sized’’ humerus is less than 35% longer than ‘‘medium-sized’’ humeri with complete or almost complete epiphyseal fusion (stages 4 and 5, see Haynes, 1991). Therefore, this ‘‘large sized’’ vs. ‘‘mediumsized’’ ratio would be consistent with the dimensional range obtained for modern populations, thus larger specimens might correspond to large adult males in a sexual dimorphism model. On the other hand, the presence of a large elephant at Contrada Fusco might suggest that Elephas antiquus sporadically visited Sicily during short periods of temporary food shortage on the mainland and, afterwards, swam back there, following a ‘‘pendal-route’’ (cfr. Palombo, 2004b).

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Even if the E. mnaidriensis FC represents just a samplesubset of the more diversied mainland community source, various elements from mainland guilds entered it. A comparison between the body-mass structure of the late Middle Pleistocene FCs from Sicily and the Italian peninsula (Torre in Pietra FU, Palombo, 2005b) demonstrates that larger middle-sized herbivores (mixed feeder deer) only slightly reduced their size on islands. On the other hand, larger herbivores (grazer bovids) shifted into the niche occupied on the mainland by large horses, the endemic hippopotamus H. pentlandi, and the elephant E. mnaidriensis respectively into those of mainland large bovids (grazers) and rhinoceroses (mixed feeders), that were vacant on the island. Conversely, no significant change in body size occurred, as expected, for large and medium-sized carnivores (Fig. 2), coherently with the relatively unchanged size of the most preferred species. 4.1.3. San Teodoro Cave — Pianetti FC The San Teodoro Cave — Pianetti FC is characterised by the occurrence of E. mnaidriensis, along with Equus hydruntinus and other continental taxa, typical of the balanced fauna belonging to the latest Pleistocene Castello FC, where no ‘‘insular’’ taxa are present. The occurrence of taxa virtually identical to continental equivalents, as well as the presence of large carnivores, testified that the filter function of the barrier between Sicily and the mainland was greatly reduced. Nonetheless, if the idea that it was possible to reach the island using a greatly increased number of easier migratory routes should be valid for the San Teodoro Cave — Pianetti FC, it apparently contrasts with the reduced diversity of the Castello FC. However, the incompleteness of the sample, taphonomic biases and the reduced biodiversity of western-southern Italy (Bonfiglio et al., 2002) during the last glacial probably affected the taxonomical composition of the Castello FC.

4.2. Sardinia The FCs thus far described for Sardinia (Palombo, 2006 and references therein) testify to the evolution towards a progressively more unbalanced and impoverished mammalian faunas. Turnover and FCs structural changes document several colonisation phases from the mainland followed by periods of a more complete isolation. Scanty remains of a dwarfed elephant (Mammuthus lamarmorai), with a withers height of about 1.5 m. and a body weight of about 800 kg, have been reported since the early 20th century in late Middle and Late Pleistocene deposits (Palombo, 2004b; Palombo et al., 2006). The LFAs found in deposits coeval to those M. lamarmorai remains have been retrieved from belong to the ‘‘Dragonara’’ faunal sub-complex (latest Middle Pleistocene-Early Holocene) (sensu Palombo, 2006). This subcomplex includes the classic endemic Sardinian fauna, where dwarfed megacerine ‘‘Praemegaceros’’ cazioti is recorded, together with the small predator Cynotherium sardous (probably feeding on the on large ochotonid Prolagus as well as young ‘‘Praemegaceros’’ cazioti calves, Novelli and Palombo, in press), endemic otters and small mammals (Table 2).

Table 2 Chronological distribution of Sardinian mammal taxa documented in Microtus (Tyrrhenicola) faunal complex (Orosei and Dragonara subcomplexes) (sensu Palombo, 2006) Selected taxa

Faunal subcomplexes “Orosei”

“Dragonara”

Talpa tyrrhenica Nesiotites similis Tyrrhenoglis figariensis Microtus (Tyrrhenicola) n.sp. Microtus (Tyrrhenicola) henseli

4.1.4. Remarks on Sicilian elephants The trend in body-mass structure of Sicilian FCs during the Middle and Late Pleistocene (Fig. 3), on the one hand seems to confirm the general nature of the ‘‘island rule’’, while on the other it underlines the relationship between the size of endemic species, and both the expansion into their fundamental niches or shifts to new ones, according to the occupancy traits of vacant species. Moreover, the absence of predator pressure contributed to drive elephants of E. falconeri FC to reach their minimal size. In addition, the insular areas might also affected the magnitude of body-size reduction if E. falconeri actually inhabited territories smaller than those settled by E. mnaidriensis. Furthermore, it is worth noting that, although limited by the low diversity of faunas, body-mass distribution within Sicilian FCs is consistent with a prevalence of more open, slightly drier environments with respect to the average conditions of the Italian peninsula (Fig. 2).

Rhagamys orthodon "Rhagapodemus" minor Oryctolagus aff. O. lacosti Prolagus sardus Megalenhydris barbaricina Sardolutra ichnusae Algarolutra majori Enhydrictis galictoides

?

Pannonictis nesti Cynotherium sp. Cynotherium sardous Macaca majori Mammuthus lamarmorai “Praemegaceros” sardus “Praemegaceros” cazioti "Caprinae" gen et sp. indet

?

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The body-mass structure of the Sardinian Microtus (Tyrrhenicola) FC (sensu Palombo, 2006) (Fig. 4) shows that if intra-guild competition diminishes, endemic species tend to attain an optimal body-size, but at the same time points out the variety of factors conditioning this process. If it is true that size reduction in M. lamarmorai may be limited by the presence of cervids, the factor limiting the size reduction of the latter is by no means clear (for instance, island surface, non-limitation in food resources or occurrence of predators (? humans), as hypothesized by Sondaar, 2000). 4.3. Crete The biochronological setting of Pleistocene mammalian fauna is based on the phylogeny of endemic murids (see for a discussion Dermitzakis and De Vos, 1987; de Vos, 1996; Meyhew, 1996 with bibliography), according to which two main FCs can be distinguished: the Kritimys FC (including the Kritimys kiridus and Kritimys catreus subcomplexes), and the Mus FC (including the Mus bateae and Mus minotaurus subcomplexes) (Table 3). The smallest endemic elephants and dwarfed hippopotamuses are the only large mammals respectively present in the Kritimys kiridus and Kritimys catreus subcomplexes, whereas larger elephants occur in the Mus minotaurus subcomplex, together with more than five endemic deer (Capasso Barbato, 1990; Caloi and Palombo, 1995; de Vos,

1996, with bibliography). In the course of time, several hypotheses have been put forward on the number and taxonomic status of endemic elephants from Crete (see Theodorou, 1986; Mol et al., 1996; Symeonidis et al., 2000; Poulakakis et al., 2002; Palombo, 2004b, with bibliography). On the basis of the evidence available, it is probable that at least two endemic elephantine species occurred in Crete, resulting from two principal immigration phases and evolutionary processes: the earlier, Mammuthus creticus, is the only large mammal in the oldest Pleistocene Kritymys kiridus FC, whereas the larger Elephas creutzburgi (however, cfr. Mol et al., 1996; Poulakakis et al., 2002; Palombo, 2004b, for a discussion). This taxon should be about 69% of the size of some E. antiquus specimens from the Middle Pleistocene on the Greek mainland (Tsoukala and Lister, 1998; Palombo, unpublished data), with a body-mass of about 2500 kg, confirming the limited dwarfing of medium-sized elephants from Crete. Specimens whose size is a little smaller or falls within the range of the mainland Elephas antiquus, have also been reported in deposits from which Mus minotaurus remains have frequently been retrieved (Mol et al., 1996; Symeonidis et al., 2000; Poulakakis et al., 2002, and references therein) . Whether such specimens belong to a third taxon or should be ascribed to the mainland E. antiquus has been extensively debated. Recently, Symeonidis et al. (2000) created a new species, Elephas chaniensis, for fossil material collected in the

Table 3 Chronological distribution of the Pleistocene mammalian taxa from Crete

Selected taxa

Faunal complexes Kritimys aff K. kiridus

Crocidura zimermanni Kritimys aff K. kiridus Kritimys kiridus Kritimys catreus Mus bateae Mus minotaurus Martes foina Meles meles Lutrogale cretensis Mammuthus creticus Elephas (Palaeloxodon) creutzburgi Elephas sp. (Elephas chaniensis/Elephas antiquus) Hippopotamus sp. Hippopotamus creutzburgi Candiacervus ropalophorus Candiacervus sp. Candiacervus cretensis Candiacervus rethymnensis Candiacervus dorotensis Candiacervus major

Kritimys kiridus

115

Kritimys catreus

Mus bateae

Mus minotaurus

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submerged cave of Vamos (Chania, West Crete), already considered a subspecies of E. antiquus (Symeonidis and Theodorou, 1982). In Symeonidis et al. (2000) opinion, the elephants from Vamos cave belong to ‘‘a large but not continental-sized’’ endemic elephant (about 20% smaller than the continental Elephas antiquus), ‘‘larger than any known specimen from the Rethymno area’’. These authors included in the same new specie also the elephant remains found at Koumpes (Rethymno) ( ¼ E. antiquus, Mol et al., 1996). However, there are many examples of modern and fossil Proboscideans showing a large intra-specific diversity. For instance, in the Hwange National Park (Zimbabwe), the size difference between smallest and largest elephants (Loxodonta Africana) is more than 20% (Haynes, 1991). On the basis of available data, the existence on Crete of a third endemic species (intermediate in size between E. creutzburgi and E. antiquus) does not seem to have been satisfactorily demonstrated. Moreover, the presence of a large elephant, not clearly endemic, might suggest that the insular populations were genetically still in contact with the mainland population (Sondaar et al., 1996). Mol et al. (1996) suggested that some Elephas antiquus might have visited Crete during periods of temporary food shortage on the mainland and afterwards swum back to the mainland. These occasional temporary migrations from the mainland could not have maintained a genetic flow between insular and continental populations. Pending the definition of the taxonomical status of the largest specimens, and taking into account the objective, only the analysis of the middlesized E. creutzburgi is here presented. The FCs thus far described for Crete (de Vos, 1996; Poulakakis et al., 2002 and references therein) denote the difficulty of colonisation permitting to very few species to reach the island, and testify the persistence of strongly unbalanced and impoverished fauna, even if an evolution towards slightly more diversification is detectable (Table 3). The structure of Crete’s FCs (Fig. 5), the size reduction of largest mammals, M. creticus and Hippototamus creutzburgi, as well as the radiation of deer, is consistent with the availability on the island of niches that on mainland are typical of large and medium-sized herbivores (perissodactyls and artiodactyls). Among endemic small mammals, the body size of the shrew in rather larger than its mainland relative. Besides, it is worth noting that the body size of endemic smallest mammals, Crocidura, progressively increased after the disappearance of the quite lager Kritimys representatives. It is worth noting that the hippopotamus seems to have reduced its size less than expected according to the vacant niches, being its average body size larger than the size of M. creticus. However, the possibility of the occurrence of populations differing, and scaling in size cannot completely ruled out (see Spaan, 1996 and references therein for a discussion). Moreover, the taxonomical composition shown by Crete’s FCs poses some questions mainly related to time of migrations and coexistence of hippopotamuses and elephants. For instance, if the occurrence of a dwarfed

hippopotamus in the Kritimys kiridus FC — already suggested by Spaan (1996) on the basis of ribs found at Siteia I, a locality where K. aff. kiridus also occurs — needs to be confirmed, on the other hand it is difficult to give justification for the absence of elephant settlers at the time of the Kritimys catreus and Mus bateae FCs. More data and further studies are certainly required to clarify this important issue, and to provide evidence for a better understanding of body size trends in endemic mammals from Crete. 4.4. Tilos and Cyprus Tilos and Cyprus, two very dissimilar islands as regards surface area, were inhabited during the Late Pleistocene by endemic elephants which were quite similar in size, both originating from E. antiquus. This evidence confirms the marginal importance of island area as a factor affecting bodysize dwarfing in endemic elephants. 4.4.1. Tilos The endemic elephant from Tilos (Theodorou, 1983, 1988; Theodorou et al., in press, and references therein), slightly larger than E. falconeri, is the only large mammal present on the island. Its continental ancestor possibly reached the island at the beginning of the last Glacial, after the extinction of endemic deer. Size reduction occurred rapidly, as has already been shown (e.g. Lister, 1996). Given the lack of intra-guild competition, the small surface area and limited productivity of the island, the question is why the endemic species from Tilos was not further reduced in size, unless we invoke overly brief isolation times or genetic introgression phenomena, which are difficult to prove. The elephant population inhabited Tilos at least from about 50 ka until 3.3 ka BP; thus Elephas n.sp. from Tilos (Theodorou et al., in press) was the latest palaeoloxodontine to survive in Europe. 4.4.2. Cyprus Some remains of a very small elephant (estimated body weight approximately 250 kg), found at Imbohary (fortysix molars) and at a few other sites in Cyprus, were first reported and described as Elephas cypriotes by Bate (1903, 1904). Moreover, seven molars belonging to a larger elephant have been recorded at Achna (Boekschoten and Sondaar, 1972; Davies and Lister, 2001). The biochronological relationships between the smaller elephant and the Achna specimens cannot be defined due to the lack or uncertainty of chronological data. E. cypriotes survived in Cyprus until at least 11 ka BP (Simmons, 1999). This fact complicates the scenario of elephant evolution in Cyprus if the larger and older Achna specimens might predate the smaller ones (Davies and Lister, 2001). Nevertheless, other hypotheses, such as sympatric speciation and radiative evolution (cfr. e.g. Harvey and Rambaut, 2000; Haskell et al., 2002), cannot be completely excluded. In any case, the three large endemic mammals, elephants and the dwarfed

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hippopotamus Phanourius minor, proportionally scale their size, shifting towards the size of herbivores vacant on the island, such as bovids, horses or large and medium sized deer. 5. Body size, metabolic rate, life-history traits, niche occupancy, home range, and related issues Body-size evolution is one of the most fundamental responses to island environments. Indeed, it influences several characteristics, including some of those regulating population dynamics on islands, such as those associated with immigration potential, reproduction rate, ecological interactions and resource requirements (Calder, 1996 and references therein). It is well known that characteristics of organisms vary predictably with their body size, temperature, and chemical composition (West et al., 2003; Brown et al., 2004; Suarez et al., 2004; Speakman, 2005; White and Seymur, 2005 and references therein). Actually, body size is crucial for synthesis in biology, since it concerns the rates of all biological structures and processes, the physiology and behaviour affecting, for instance, interactions between organisms and their environment (e.g. home-range size and population density) (see inter alios Peters, 1983; Damuth, 1993; Demetrius, 2000; Haskell et al., 2002; Jetz et al., 2004 and references therein). Since the 20th century, it has been widely recognised that body size and metabolic rate are dependent variables. Huxley (1932) stressed that most size-related variations (such as metabolic rate, development time, population growth rate) can be described by allometric equations, power functions of body-mass according to the formula bY ¼ YoMh. These relationships are known as the ‘‘quarter-power’’ scaling law, the scaling exponents being multiples of 14. The strict relationship between animal size and metabolic rate involves several biological, physiological and ecological aspects. Metabolism, for instance, regulates individual biomass production, ontogenetic growth (e.g. Brown et al., 2004 stressed that ‘‘trees and vertebrates of the same body-mass, operating at the same body temperature, produce new biomass through some combination of growth and reproduction, at very similar rates’’), life-span expectancy, survival times and mortality rates, which also mean population growth and extinction risk, even if survival and mortality are also greatly affected by extrinsic environmental conditions (cfr. e.g. Speakman, 2005; White and Seymur, 2005 and references therein). 5.1. Large or small? Does an ‘‘optimal’’ size actually exist? Even if the nature of scaling between organismal basal metabolic rate and body-mass is still a widely debated issue as far as theoretical biology is concerned (Blueweiss et al., 1978; Bartholomew, 1981; Makarieva et al., 2003; Savage et al., 2004; Suarez et al., 2004), general agreement exists on the allometric scaling law regulating the dependence of biological variables on body-mass. For instance, it was

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claimed that the resting metabolic rate scales as 34 power of body-mass (Andresen et al., 2002), and the life-span and maximal population growth scale as 14 power (West et al., 1997, 2003). Moreover, it was suggested that the maximum efficiency of organisms corresponds to minimum overall entropy production, and organisms produce entropy as the intrinsic rate of 34 power of body size (Andresen et al., 2002). Moreover, the field metabolic rate (expressing the total energy budget of the animal) is linked to food requirements (see Christiansen, 2004, for a discussion on elephants). In Damuth’s opinion (1993), the energetic optimum would be attained at 1 kg body-mass, while Brown et al. (1993) suggested optimal body size might be 100 g. Some scientists have suggested that the ‘‘optimal’’ size for species of a particular bau plan and ecological strategy would be represented by the body size of insular populations whose size tends not to diverge from that of their mainland counterparts (cfr. Lomolino, 2005). This would be particularly true when, in quite stable environmental conditions, outstandingly low biodiversity reduces intraguild, as well as interspecific, competition. Moreover, a sort of relationship exists among area, size and the number of individuals that a particular species can pack into a given area (area–scaling hypothesis by Marquet and Taper, 1998), which should favour the dwarfing of large mammals on islands, particularly on the smallest ones. If an ‘‘optimum body size’’ actually exists (cfr. also Blackburn and Gaston, 1996; Jones and Purvis, 1997; Purvis and Harvey, 1997; Kozlowski and Gawelczyk, 2002; Boback and Guyer, 2003), it can be hypothesised that, as far as large mammals are concerned, given the intrinsic characteristics connected with their bau-plan, and removing biotic and abiotic environmental constraints, large mammals would miniaturise, whereas small ones would increase in size. Accordingly, the body size of insular species could shift, within a given guild, towards the body size of vacant species and converge on a size optimal for a particular bau-plan and ecological behaviour, which can be considered consistent with the empirical evidence of the ‘‘island rule.’’ However, evolutionary trends in endemic taxa also involved occupying or creating novel niches, possibly modifying-original bau-pla¨ne. Hence, heterotopy can produce new morphologies along trajectories different from those that generated ancestral forms (Zelditch and Fink, 1996), as exemplified by radiative evolutionary processes, already well known in Darwin’s finches, or undergone, for example, by Pleistocene deer in Crete (Caloi and Palombo, 1995; de Vos, 1996, 2000). 5.2. What advantages does size reduction give elephants? Large mammals undoubtedly derive some advantages from reducing their size. For instance, larger individuals require more food, and larger-sized mammals generally need larger home ranges; hence only large landmasses are able to support at least the necessary minimum number of

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individuals to avoid the risk of extinction. Accordingly, the body-mass of the top species was found to become greater as available land area increased (cfr. Burness et al., 2001). Actually, large herbivores such as elephants spend a huge amount of energy and time foraging (however, see Christiansen, 2004; Clauss and Hummel, 2005); thus dwarfed individuals might be favoured not only on small islands but also in more favourable environmental conditions, for example on a large island like Sicily, Crete or Santa rosae, as far as Mammuthus exilis is concerned. Moreover, since body size correlates with population density, the need to attain the critical minimum number of specimens required to avoid the threat of extinction caused by low density of the pioneer population might explain the insular dwarfing phenomenon in large mammals. In addition, it is well known that life-history traits, related to growth and reproduction, vary greatly not only among species, but also within the same species, depending on, for example, population density. Accordingly, changes in body size and metabolic rate should lead to a higher reproduction rate which, in turn, allows population size to remain at a relatively high, constant level. This reasoning is also more or less coherent with the theoretical basis of the ‘‘life history’’ approach (e.g. Oli and Dobson, 2003 and references therein). However, the ‘‘life history’’ hypothesis formulated by Palkovacs (2003) does not rely on particular selective pressures but on general life-history responses to environmental changes encountered on islands, including a reduced extrinsic mortality rate and decreased resource levels; the latter, in a life-history context, may be expected to result in genetic and phenotypically plastic responses in age and size at maturity, and the degree of body-size change relative to the mainland ancestor. Taking all this into consideration, dwarfed elephants were probably selected to give birth after a progressively shorter pregnancy period and at a lower body weight than their mainland ancestors (Raia et al., 2003). Indeed, the great modification in the skull, characterising most dwarfed elephants, and possibly the relative shortening of limbs, are related to paedomorphosis processes (Palombo, 2004b). For instance, dwarfing by paedomorphosis has been recognised in the Late Cretaceous titanosaurid sauropod, Magyarosaurus dacus, from Transylvania (Jianu and Weishampel, 1999). In addition, it is worth noting that a reduction in genetic variation might be important in endemic island mammalian populations (Frankham, 1997), since ‘‘population bottlenecks associated with founder events, and small population sizes on islands might seriously erode genetic variation’’ (Pergams and Ashley, 2001). A higher reproductive rate increases population density and may preserve heterozygosis, thereby avoiding the threat of extinction. Clearly, changes in environmental conditions and selective pressure guide evolutionary trends. Heaney (1978) suggested that food limitations and predation and/or interspecific competition are respectively

the most important factors on small and large islands. Actually, there is a body-size threshold (about 150 kg) above which ungulate species have few natural predators and exhibit higher food limitation, as recently demonstrated for small ungulates inhabiting the Serengeti reserve (Sinclair et al., 2003). In any case, inter- or intra-guild competition is acknowledged as a phenomenon affecting dwarfing. For example, reduced dwarfing in the largest endemic elephants (such as the Sicilian specimens belonging to the E. mnaidriensis group or the Crete Elephas creutzburgi) could be evaluated in the light of the presence of a competitor, notably deer, whereas no competitors were present in those oligotypical faunas in which most dwarfed elephant have occurred (e.g. E. falconeri and M. creticus). On the other hand, it is worth noting that, in the case of endemic elephants, the most highly dwarfed taxa (e.g. Sicilian E. falconeri) have been recorded in faunas where no other large mammals are present, whereas the largest-sized taxa occurred in more diversified faunas (e.g. Sicilian E. mnaidriensis or Crete E. creutzburgi), (Palombo, 2004b, and references therein). In addition, other large herbivores displayed similar trends, shifting their size to varying extents towards one permitting them to broaden their own niche or to occupy the niche of species of their own guild not present on the island. This is the case with the large endemic herbivores of the E. mnaidriensis FC in Sicily. On the other hand, as far as Crete is concerned, De Vos (1996) pointed out that the presence of a wide variety of endemic deer in Crete at the time a large elephant colonised the island, might have prohibited this elephant from undergoing more marked size reduction. Accordingly, we might suppose that, by reducing their size, large herbivores have increased possibilities of optimising energy costs and exploiting environmental opportunities, all other factors being equal; they thus affect evolutionary trends on islands or in island-like environments, as the dwarfing process largely depends on the nature of vacant, empty herbivore niches. Conversely, small mammals enlarging their size should reduce their metabolic rate and food requirements, increasing their life expectancy. However, it is worth noting that in extant insular shrews, whose island populations are characterised by an increase in size and morphological, ecological, demographical and behavioural changes, the evolution of shrew metabolism on islands seems partially independent of body-mass increase, and other selective forces (changes in resource availability, decrease in competition and predation pressures) can play a part in size and physiological adjustments (Magnanou et al., 2005). On the other hand, an increase in adult body size, associated with a decrease in litter size, has been demonstrated for Crocidura suaveolens from Corsica (Fons et al., 1997). Hence, if our reasoning is correct, in insular communities, differing from the mainland because they are unbalanced, ecologically simple and encompass empty niches, the body size of species might generally converge towards an ‘‘optimal size’’: larger species undergo

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dwarfism, smaller species gigantism. Moreover, since species of optimal size maintain the highest population density, large mammals should be more able to avoid extinction risk, small mammals to prevent overcrowding. Such convergence towards an ‘‘optimum’’ has been already stressed by Thaler (1973), who claimed that the presence of carnivores allows mainland mammals to become giant or dwarfed with respect to their fundamental size. Nonetheless, the size changes undergone by insular taxa are a complex phenomenon, and the significance of some ‘‘exceptions’’ cannot be neglected. For instance, as regards Carnivora, several changes in size have been reported; for example, Goltsman et al. (2005) described the difference in body size and increased population density of the fox population on Mednyi Island as the ‘‘Island syndrome,’’ whereas Meiri et al. (2004, 2005a, b) pointed out that patterns observed in insular carnivores provide no support for theories proposing a single optimal size. Actually, size of insular carnivores mainly depend on the size of the available or preferred prey. For instance, the peculiar evolution of Sardinian otters, including the ‘‘giant’’ Megalenhydris barbaricina, could be explained with the tendency of species with aquatic prey to have a larger than optimum size, since they are much less constrained by the limited terrestrial resources on islands than are more terrestrial mammals (McNab, 2002; Lomolino, 2005). Therefore, more studies are needed to understand the general meaning of ‘‘optimal size’’, if such a thing actually exists, within species having similar or fundamentally different bau-pla¨ne or different feeding strategies. 6. Conclusions The body-size trend displayed by dwarfed elephants, as well as the shift in size of endemic Pleistocene mammals from Mediterranean islands, confirms that the ‘‘island rule’’ remains a real and quite general pattern (at least as far as non-carnivorous mammals is concerned), resulting from a relatively complex combination of factors. The limited area of islands, resource shortage, ecological release and low richness have been often regarded as the key elements driving size evolution on islands. Nevertheless, as discussed by several authors, it is not a simple task to pinpoint which among several elements induced elephants to adapt to a niche where a smaller size would be required, as well as insular mammals to change their body-size across a range of spatial and temporal scales, apparently in a way not directly dependent on the island surface or its distance from the mainland (which reduces the number of immigrant species). What mechanism causes large herbivores to become dwarfs or exceptionally increase their size, carnivores to become smaller, larger or to remain unchanged, and small mammals to display such great variability in patterns? Body-size is undoubtedly the main factor influencing organism morphology, physiology, life history (hence its

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role within a community) and thus in turn the intrinsic properties of the species and, according to the ‘‘niche occupancy rules,’’ interaction with the habitat and with other members f the community. Indeed, differences in some aspects of their traits, or responses to the environment allow species to coexist in the same habitat. In the absence of immigration, competitive exclusion tends to create a regular spacing of niches, and vacancy of niches depends on richness, and especially on species traits as well as inter- and intra-guild competition. A ‘‘neutral theory’’ of community structure (and as stated above, body-size is a central aspect of such a structure) has recently been developed as an alternative to traditional niche theory (Hubbell, 2001). In the neutral theory, species are assumed to be ecologically identical, and species diversity is considered merely a function of metacommunity size. To understand ‘‘the island rule’’ in the light of ‘‘neutral theory’’ is not a simple task. Nonetheless, some aspects of this theory should be taken into account. For instance, Gravel et al. (2006) stressed that ‘‘niche and neutrality form ends of a continuum from competitive to stochastic exclusion.’’ Thus, differences in selective pressure among insular species of different size due to an absence of species that cannot migrate to islands for predictable or less predictable (‘‘stochastic’’) reasons, should favour a tendency to converge towards ‘‘optimal’’ size, particular baupla¨ne and ecological strategies. Evaluating various factors (island size and physiography, climate and microclimate, distance from the coast, duration of isolation, number and type of immigrant taxa, pre-existing taxa, population density, extinction rates, etc.), we must keep in mind that as far as elephants are concerned, on the one hand species undergoing similar size reductions occurred on islands that differ in area, physiography and primary productivity, while on the other hand, it is worth noting that, in the case of endemic elephants, the most dwarfed taxa occurred in faunas where no other large mammal appeared, whereas the largest taxa appeared in more diversified faunas; it seems that elephant dwarfing involved shifts and expansions in their fundamental niches, converging towards particular traits of vacant species, like some artiodactyls. Indeed, the ‘‘competition’’ factor seems to be of more weight in dwarfing processes, and body-size shift seems to be regulated at the guild level, as intra-guild competition could affect bodysize decrease. Moreover, taking into account the rapid changes in body-size (Lister, 1989, 1996), paedomorphic growth (Palombo, 2001) and high reproduction rate (Raia et al., 2003) characterising the smallest elephants, we might suppose that dwarfing responds to the equation that the smaller the individuals in a population are, the less food is required within a trophic level, and therefore the larger the number of individuals making up the population, the greater the genetic exchange. If this reasoning is correct, in an insular environment, due to lack of direct inter- and intra-guild competition, large herbivores and small mammals would respectively

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reach their minimum and maximum body-size compatible with their bau-pla¨ne, following niche occupancy rules (sensu Lachance et al., 2003). This means that, depending on the free niches available on an island, large and small mammals tend to reach the ecotypic patterns or ‘‘critical sizes’’ allowing the best energetic balance. Further study is certainly required to provide evidence for this hypothesis, but it should be a promising area for future studies on body-size evolution in insular vertebrates. Acknowledgments I am indebted to those many colleagues who discussed with me the several topics that created the framework of this study, as well as with the people at the numerous museums and institutions I visited (Aristotle University of Thessaloniki; Institut de Paleontoloı` a ) Miguel CrusafonPairc- , Sabadell; Institut de Pale´ontologie Humaine, Paris; Institut Mediterrani d’Estudis Avancat, Palma de Mallorca; Instituut Voor Aardwetenschappen, Utrecht; Istituto Italiano di Paleontologia Umana, Rome; Museo Archeologico, Nuoro; Museo Archeologico Regionale ‘‘Paolo Orsi’’, Siracusa; Museo Cvico ‘‘A. Doria’’, Genua; Museo Civico di Zoologia, Roma; Museo di Paleontologia, Universita` degli Studi di ‘‘Federico II’’ di Napoli, Napoli; Museo di Paleontologia, Universita` degli Studi di Cagliari, Cagliari; Museo di Paleontologia, Universita` degli Studi di Catania, Catania; Museo di Paleontologia, Universita` degli Studi di Padova, Padua; Museo di Paleontologia, Universita` degli Studi di Roma ‘‘La Sapienza’’, Rome; Museo di Storia Naturale, sez. Geo-Paleontologica, Universita` degli Studi di Firenze, Florence; Museo di Storia Naturale ‘‘La Specola’’, Florence; Museo Geologico ‘‘G. Gemellaro’’, Universita` degli Studi di Palermo, Palermo; Museo Nacional de Ciencias Naturales, Madrid; Museo Preistorico di Pofi, Pofi (Frosinone); Museo Preistorico Etnografico ‘‘L. Pigorini’’, Rome; Muse´um d’Histoire Naturelle, Paris; Museum of Ghar Dalam Cave, Malta; Museum of Palaeontology and Geology, University of Athens, Athens; Nationaal Natuurhistorisch Museum, Leiden; Natural History Museum, London; Naturhistorisches Museum, Basel; Soprintendenza ai Beni Archeologici delle province di Sassari e Nuoro, Nuoro; Soprintendenza ai Beni Archeologici di Roma, Rome) for granting me access to the fossil material in their care and for their help. I thank the two anonymous reviewers for their comments on this manuscript. The English version has been revised by Dr. Mary Groeneweg, English Language Lecturer at Cagliari University. References Adler, G.H., Levins, R., 1994. The island syndrome in rodent populations. Quarterly Review of Biology 69, 473–490. Alberdi, M.T., Prado, J.L., Ortiz-Jaureguizar, E., 1995. Patterns of body size changes in fossil and living Equini (Perissodactyla). Biological Journal of the Linnean Society 54, 349–370.

Alcover, J.A., Moya`-Sola`, S., Pons-Moya`, J., 1981. Les quimeres del passat. Els vertebrats fo`ssils del Plio-Quaternari de les Balears i Pitiu¨ses. Memories de la Institucio´ Catalana d’Historia Natural 11, 1–265. Alcover, J.A., Sans, A., Palmer, M., 1998. The extent of extinction of mammals on islands. Journal of Biogeography 25, 913–918. Anderson, J.F., Hall-Martin, A., Russel, D.A., 1985. Long-bone circumference and weight in mammals, birds and dinosaurs. Journal of Zoology 207, 53–61. Anderson, R.P., Handley Jr,, C.O., 2002. Dwarfism in insular sloths, biogeography, selection, and evolutionary rate. Evolution 56, 1045–1058. Andresen, B., Shiner, J.S., Uehlinger, D.E., 2002. Allometric scaling and maximum efficiency in physiological eigen time. Proceedings, National Academy of Science 99 (9), 5822–5824. Angerbjo¨rn, A., 1986. Gigantism in island populations of wood mice (Apodemus) in Europe. Oikos 47, 47–56. Azzaroli, A., 1982. Insularity and its Effects on Terrestrial Vertebrates, Evolutionary and Biogeographic Aspects. In: Montanaro Galitelli, E. (Ed.), Palaeontological Essentials of Historical Geology. Modena, pp. 18–23. Badano, E.I., Regidor, H.A., Nunez, H.A., Acosta, R., Gianoli, E., 2005. Species richness and structure of ant communities in a dynamic archipelago, effects of island area and age. Journal of Biogeography 32, 221–227. Bartholomew, G.A., 1981. A matter of size: an examination of endothermy in insects and terrestrial vertebrates. In: Heinrich, B. (Ed.), Insect Thermoregulation. Wiley, New York, USA, pp. 45–78. Basile, B., Chilardi, S. (Eds.), 1996. Siracusa, le ossa dei giganti. Lo scavo paleontologico di Contrada Fusco. Arnaldo Lombardi, Siracusa, Palermo. Bate, D.M.A., 1903. Preliminary note on the discovery of a pygmy elephant in the Pleistocene of Cyprus. Proceedings, Royal Society of London 71, 498–500. Bate, D.M.A., 1904. Further note on the remains of Elephas cypriotes from a cave-deposit in Cyprus. Philosophical Transactions, Royal Society of London B 197, 347–360. Bernardello, G., Anderson, G.J., Stuessy, T.F., Crawford, D.J., 2001. A survey of floral traits, breeding systems, floral visitors, and pollinator systems of the angiosperms of the Juan Fernandez Islands (Chile). Botonical Review 67, 255–308. Blackburn, T.M., Gaston, K.J., 1996. On being the right size: different definition of ‘‘right’’. Oikos 75, 345–351. Blueweiss, L., Fox, H., Kudzma, V., Nakashima, D., Peters, R., Sams, S., 1978. Relationships between body size and some life history parameters. Oecologia 37, 257–272. Boback, S.M., 2003. Body size evolution in snakes, evidence from island populations. Copeia 2003, 81–94. Boback, S.M., Guyer, C., 2003. Empirical evidence for an optimal body size in snakes. Evolution 57, 345–351. Boekschoten, G.J., Sondaar, P.Y., 1972. On the fossil Mammalia of Cyprus. I–II Proceedings, Koninklijke Nederlandse Akademie van Wetenschappen 75, 306–338. Bonfiglio, L., Mangano, G., Marra, A.C., Masini, F., Pavia, M., Petruso, D., 2002. Pleistocene Calabrian and Sicilian bioprovinces. Geobios, Special Memoir 24, 29–39. Bover, P., Alcover, J.A., 2005. A taxonomic approach to the insular caprines of the Gymnesic Islands (western Mediterranean Sea). In: Cre´gut-Bnnoure, E. (Ed.), Les Ongule´s Holarctiques du Plioce`ne et du Ple´istoce`ne. Quaternarie hors213-220-se`rie 2. Brown, J.H., 1971. Mammals on mountaintops, non-equilibrium insular biogeography. American Naturalist 105, 467–478. Brown, J.H., Lomolino, M.V., 1998. Biogeography, second ed. Sinauer Associates, Inc., Sunderland, MA, USA. Brown, J.H., Marquet, P.A., Taper, M.L., 1993. The evolution of body size, consequence of an energetic definition of fitness. American Naturalist 142, 573–584.

ARTICLE IN PRESS M.R. Palombo / Quaternary International 169–170 (2007) 105–124 Brown, J.H., Gillooly, J.F., Allen, A.P., Savage, VanM., West, G.B., 2004. Toward a metabolic theory of ecology. Ecology 85, 1771–1789. Brown, P., Sutikna, T., Morwood, M.J., Soejono, R.P., Jatmiko, Saptomo, W.W., Due, R.A., 2004. A new small-bodied hominin from the Late Pleistocene of Flores, Indonesia. Nature 431, 1055–1061. Burgio, E., 1997. Le attuali conoscenze sui mammiferi terrestri quaternari della Sicilia. In: Tusa, S. (Ed.), Prima Sicilia, alle origini della societa` siciliana. Ediprint, Palermo, pp. 54–71. Burness, G.P., Diamond, J., Flannery, T., 2001. Dinosaurs, dragons, and dwarfs. The evolution of maximal body size. Proceedings, National Academy of Science 98, 14518–14523. Calder, W., 1996. Size, Function and Life History. Dover, Olineole NY, USA. Caloi, L., Palombo, M.R., 1989. Oligotipia nelle mammalofaune insulari. Atti 31 Simp. Ecologia e Paleoecologia delle comunita` bentoniche, Catania-Taormina, Catania, pp. 259–283. Caloi, L., Palombo, M.R., 1995. Functional aspects and ecological implications in Pleistocene endemic cervids of Sardinia, Sicily and Crete. Geobios 28, 247–258. Capasso Barbato, L., 1990. Les cervide´s ende´miques de Cre`te. Quaternaire 3–4, 265–270. Carlquist, S., 1974. Island Biology. Columbia University Press, New York. Carlquist, S., 1980. Hawaii a Natural History, second ed. SB Printers, Inc., Linton, UK. Carvajal, A., Alder, G., 2005. Biogeography of mammals on tropical Pacific islands. Journal of Biogeography 32, 1561–1569. Case, T.J., 1978. A general explanation for insular body size trends in terrestrial vertebrates. Ecology 59, 1–18. Case, T.J., Bolger, D.T., 1991. The role of interspecific competition in the biogeography of island lizards. Trends in Ecology and Evolution 6, 135–139. Case, T.J., Faaborg, J., Sidell, R., 1982. The role of body size in the assembly of West Indian bird communities. Evolution 37, 1062–1074. Chilardi, S., 2001. Gli elefanti di C.da Fusco (Siracusa, Sicilia): analisi integrata dei dati paleoambientali. In: Cavarretta, G., Gioia, P., Mussi, M., Palombo, M.R. (Eds.), The World of Elephants. CNR, Roma, pp. 476–478. Christiansen, P., 2004. Body size in proboscideans, with notes on elephant metabolism. Zoological Journal of the Linnean Society 140, 523–549. Clauss, M., Hummel, J., 2005. The digestive performance of mammalian herbivores: why big may not be that much better. Mammal Reviews 35, 174–187. Clegg, S.M., Owens, I.P.F., 2002. The ‘island rule’ in birds, medium body size and its ecological explanation. Proceedings of the Royal Society of London, Series B 269, 1359–1365. Croft, D.A., Heaney, L.R., Flynn, J.J., Bautista, A.P., 2006. Fossil remains of a new, diminutive Bubalus (Artiodactyla: Bovidae: Bovini) from Cebu island, Philippines. Journal of Mammalogy 87, 1037–1051. Damuth, J., 1993. Cope’s rule, the island rule and the scaling of mammalian population density. Nature 365, 748–750. Darlington Jr., P.J., 1943. Carabidae of mountains and islands: data on the evolution of isolated faunas, and atrophy of wings. Ecological Morphology 13, 37–61. Davies, P., Lister, A.M., 2001. Palaeoloxodon cypriotes, the dwarf elephant of Cyprus, size and scaling comparisons with P. falconeri (Sicily-Malta) and mainland P. antiquus. In: Cavarretta, G., Gioia, P., Mussi, M., Palombo, M.R. (Eds.), The World of Elephants. Consiglio Nazionale Richeche, Roma, pp. 479–480. Dayan, T., Simberloff, D., 1996. Community ecology and character displacement in carnivores. In: Gittleman, J.L. (Ed.), Carnivore Behavior, Ecology, and Evolution. Cornell University Press, Ithaca, New York, pp. 243–266. Dayan, T., Simberloff, D., 1998. Size patterns among competitors: ecological character displacement and character release in mammals, with special reference to island populations. Mammal Review 28, 99–124.

121

De Vos, J., 1996. Taxonomy, ancestry, and speciation of the endemic pleistocene deer of crete compared with the taxonomy, ancestry, and speciation of Darwin’s Finches. In: Reese, D.S. (Ed.), Pleistocene and Holocene Fauna of Crete and its first Settlers. Monographs in World Archaeology 28, 99–110. De Vos, J., 2000. Pleistocene deer fauna in crete: its adaptive radiations and extinction. Tropics 10, 125–134. Delson, E., Terranova, C.J., Jungers, W.L., Sargis, E.J., Jablonski, N.G., Dechow, P.C., 2000. Body-mass in Cercopithegidae (Primates, Mammalia), Estimation and Scaling in Estimation and Scaling in Extinct and extant taxa. American Museum of Natural History, Anthropological Papers, vol. 83, New York, 159pp. Demetrius, L., 2000. Directionality theory and the evolution of body size. Proceedings of the Royal Society of London, Series B 267, 2385–2391. Dermitzakis, M.D., De Vos, J., 1987. Faunal succession and the evolution of mammals in Crete during the Pleistocene. Neues Jahrbuch Geologisher und Palaontologischer, Abhandlungen 173, 377–408. Diamond, J.M., 1987. Did Komodo dragons evolve to eat pygmy elephants? Nature 326, 832. Diamond, J.M., May, R.M., 1976. Island biogeography and the design of natural reserves. In: May, R.M. (Ed.), Theoretical Ecology. Blackwell, Oxford, pp. 228–252. Drake, D.R., Mulder, C.P.H., Towns, D.R., Daughterty, C.H., 2002. The biology of insularity. Journal of Biogeography 29, 563–569. Endo, H., Hayashi, Y., Yamazaki, K., Motokawa, M., Pei, J.-C.K., Lin, L.-K., Chou, C.-H., Oshida, T., 2002. Geographical variation of mandible size and shape in the wild pig (Sus scrofa) from Taiwan and Japan. Zoological Studies 41, 452–460. Fanfani, F., 2000. Revisione degli insettivori (Mammalia) tardo neogenici e quaternari dell’Italia peninsulare. Ph.D. Thesis, Universita` di Modena and Reggio Emilia, Modena, 283pp. Ferretti, M.P., 1998. Gli elefanti del Plio-Pleistocene dell’Italia. Doctoral Thesis, Modena, Bologna, Firenze, and Roma Associated Universities, 119pp. Filin, I., Ziv, Y., 2004. New theory of insular evolution, unifying the loss of dispersability and body-mass change. Evolutionary Ecology Research 6, 115–124. Fons, R., Poitevin, F., Catalan, J., Croset, H., 1997. Decrease in litter size in the shrew Crocidura suaveolens (Mammalia, Insectivora) from Corsica (France), evolutionary response to insularity? Canadian Journal of Zoology 75, 954–958. Foster, J.B., 1964. Evolution of mammals on islands. Nature 202, 234–236. Fox, B.J., Fox, M.D., 2000. Factors determining mammal species richness on habitat islands and isolates, habitat diversity, disturbance, species interactions and guild assembly rules. Global Ecology and Biogeography 9, 19–37. Frankham, R., 1997. Do island populations have less genetic variation than mainland populations? Heredity 78, 311–327. Freudenthal, M., 1972. Deinogalerix koenigswaldi nov. gen., nov. spec., a giant insectivore from the Neogene of Italy. Scripta Geologica 14, 1–19. Ganem, G., Granjon, L., Ba, K., Duplantier, J.-M., 1995. Body size variability and water balance: a comparison between mainland and island populations of Mastomys huberti (Rodentia: Muridae) in Senegal. Experientia 51, 402–410. Gaston, K.J., Chown, S.L., Mercer, R.D., 2001. The animal species–body size distribution of Marion Island. Proceedings, National Academy of Science 98 (25), 14493–14496. Gentile, G., Argano, R., 2005. Island biogeography of the Mediterranean Sea: the species—area relationship for terrestrial isopods. Journal of Biogeography 32, 1715–1726. Gingerich, P.D., Smith, B.H., Rosenberg, K., 1982. Allometric scaling in the dentition of primates and prediction of body weight from tooth size in fossils. American Journal of Physical Anthropology 58, 81–100. Giovinazzo, C., Altamura, S., Palombo, M.R., 2006. Determinazione della massa corporea nei ruminanti di media e piccolo taglia: un nuovo

ARTICLE IN PRESS 122

M.R. Palombo / Quaternary International 169–170 (2007) 105–124

approccio metodologico. In: Fonda, G., Melis, R., Romano, R. (Eds.), Abstracts Giornate Paleontologia 2006, Trieste 8–10 giugno, 39. Givinish, T.J., 1998. Adaptive plant evolution on islands, classical patterns, molecular data, new insights. In: Grant, P.R. (Ed.), Evolution on Islands. Oxford University Press, New York, pp. 281–304. Goltsman, M., Kruchenkova, E.P., Sergeev, S., Volodin, I., Macdonald, D.W., 2005. ‘Island syndrome’ in a population of Arctic foxes (Alopex lagopus) from Mednyi Island. Journal of Zoology 267, 405–413. Gordon, K.R., 1986. Insular evolutionary body size trends in Ursus. Journal of Mammalogy 67, 395–399. Gould, G.C., MacFadden, B.J., 2004. Gigantism, dwarfism, and Cope’s Rule, ‘Nothing in evolution makes sense without a phylogeny’. Bulletin of the American Museum of Natural History 285, 219–237. Grant, P.R., 1998. Evolution on Islands. Oxford University Press, New York. Gravel, D., Canham, C.D., Beaudet, M., Messier, C., 2006. Reconciling niche and neutrality: the continuum hypothesis. Ecology Letters 9, xx–xxx. Hanski, I., 1992. Inferences from ecological incidence functions. American Naturalist 139, 657–662. Harvey, P.H., Rambaut, A., 2000. Comparative analyses for adaptive radiations. Philosophical Transactions, Royal Society of London B 355, 1599–1650. Haskell, J.P., Ritchie, M.E., Oliff, H., 2002. Fractal geometry predicts varying body size scaling relationships for mammal and bird home ranges. Nature 418, 527–530. Haynes, G., 1991. Mammoths, Mastodonts and Elephants. Biology, Behavior and the Fossil Record. Cambridge University Press, Cambridge. Heaney, L., 1978. Island area and body size of insular mammals, evidence from tri-colored squirrel (Callosciurus prevosti) of Southeast Asia. Evolution 3, 51–56. Heaney, L.R., 1986. Biogeography of mammals in Southeast Asia: estimates of rates of colonization, extinction, and speciation. Biological Journal of the Linnean Society 28, 127–165. Heaney, L.R., 2000. Dynamic disequilibrium, a long-term, large-scale perspective on the equilibrium model of island biogeography. Global Ecology and Biogeography 9, 59–74. Hoekstra, H.E., Fagan, H.P., 1998. Body size, dispersal ability and compositional disharmony of the carnivore-dominanted fauna of the Kuris Island. Diversity and Distribution 4, 135–149. Hooijer, D.A., 1949. Mammalian evolution in the Quaternary of southern and Eastern Asia. Evolution 3, 125–128. Hooijer, D.A., 1951. Pygmy elephant and giant tortoise. Science Monthly 72, 3–8. Hooijer, D.A., 1976. Observations on the pygmy mammoths of the Channel Islands, California. In: Churcher, C.S. (Ed.), Essays on palaeontology in honour of Loris Shano Russell, Royal Ontario Museum, Toronto, Canada, pp. 220–225. Hubbell, S.P., 2001. A Unified Neutral Theory of Biodiversity and Biogeography. Princeton University Press, Princeton, New Jersey, USA. Hutchinson, G.E., 1959. Homage to Santa Rosalia or why are there so many kinds of animals? American Naturalist 93, 145–159. Huxley, J.S., 1932. Problems of Relative Growth. Methuen, London, UK. Jessop, T.S., Madsen, T., Sumner, J., Rudiharto, H., Phillips, J.A., Ciofi, C., 2006. Maximum body size among insular Komodo dragon populations covaries with large prey density. Oikos 112, 422–429. Jetz, W., Carbone, C., Fulford, J., Brown, H.J., 2004. The Scaling of Animal Space use Science 306, 266–268. Jianu, C-M., Weishampel., D.B., 1999. The smallest of the largest, a new look at possible dwarfing in sauropod dinosaurs. Geologie en Mijnbouw 78, 335–343. Johnson, K.P., Adler, F.R., Cherry, J.L., 2000. Genetic and phylogenetic consequences of island biogeography. Evolution 54, 387–396. Jones, K.E., Purvis, A., 1997. An optimum body size for mammals? Comparative evidence from bats. Functional Ecology 11, 751–756.

Keogh, J.S., Scott, A.W., Hayes, C., 2005. Rapid and repeated origin of insular gigantism and dwarfism in Australian tiger snakes. Evolution 59, 226–233. Kozlowski, J., Gawelczyk, A.T., 2002. Why are species’ body size distributions usually skewed to the right? Functional Ecology 16, 419–432. Krzanowski, A., 1967. The magnitude of islands and the size of bats (Chiroptera). Acta Zoologica Cracoviensia 12, 281–346. Lachance, M.-A., Bowles, J.M., Starner, W.T., 2003. Geography and niche occupancy as determinants of yeast biodiversity, the yeast-insectmorning glory ecosystem of Kipuka Piaili, Hawai’i. Federation of European Microbiological Societies Yeast Research 4, 105–111. Lawlor, T.E., 1982. The evolution of body size in mammals, evidence from insular population in Mexico. American Naturalist 119 (1), 54–72. Legendre, S., 1986. Analysis of mammalian communities from the late Eocene and Oligocene of Southern France. Palaeovertebrata 16, 191–212. Legendre, S., 1989. Les communaut0 es de mammif‘eres du Pale´oge`ne (Eoce`ne supe´rieur et Oligoce´ne) d’Europe occidentale: Structures, milieux et 0 e´volution. Mu¨nchner Geowissenchaftliche Abhandlungen 16 (A), 1–110. Legendre, S., Roth, C., 1988. Correlation of carnassial tooth size and body weight in recent carnivores (Mammalia). Historical Biology 1, 85–98. Lister, A.M., 1989. Rapid dwarfing of red deer on Jersey in the last interglacial. Nature 342, 539–542. Lister, A.M., 1996. Dwarfing in island elephants and deer, processes in relation to time of isolation. Symposia, Zoological Society of London 69, 277–292. Lomolino, M.V., 1985. Body size of mammals on islands. The island rule re-examined. American Naturalist 125, 310–316. Lomolino, M.V., 1986. Mammalian community structure on islands, immigration, extinction and interactive effects. Biological Journal of the Linnean Society 28, 1–21. Lomolino, M.V., 2000a. A call for a new paradigm of island biogeography. Global Ecology and Biogeography 9, 1–6. Lomolino, M.V., 2000b. A species-based theory of insular zoogeography. Global Ecology and Biogeography 9, 39–58. Lomolino, M.V., 2005. Body size evolution in insular vertebrates, generality of the island rule. Journal of Biogeography 32, 1683–1699. Lomolino, M.V., Sax, D.F., Riddle, B.R., Brown, J.H., 2006. The island rule and a research agenda for studying ecogeographical patterns. Journal of Biogeography 33, 1503–1510. Lomolino, M.V., Weiser, R., 2001. Towards a more general species—area relationship, diversity on all islands, great and small. Journal of Biogeography 28 (4), 431–445. Maccagno, A.M., 1962. Gli elefanti fossili di Riano (Roma). Geologica Romana 1, 1–33. MacArthur, R.H., Wilson, E.O., 1967. The Theory of Island Biogeography. Princeton University Press, Princeton, New Jersey. Magnanou, E., Fons, R., Blondel, J., Morand, S., 2005. Energy expenditure in Crocidurinae shrews (Insectivora): Is metabolism a key component of the insular syndrome? Comparative Biochemistry and Physiology A 142, 276–285. Maiorana, V.C., 1990. Evolutionary strategies and body size. In: Damuth, J., MacFadden, B.J. (Eds.), Body Size in Mammalian Paleobiology Estimation and Biological Principles. Cambridge University Press, Cambridge, pp. 69–102. Makarieva, A.M., Gorshkov, V.G., Bai-Lian, L., 2003. Letter to the Editor. A note on metabolic rate dependence on body size in plants and animals. Journal of Theoretical Biology 221, 301–307. Malatesta, A., 1986. Meccanismi evolutivi in ambiente insulare. Bolletino della Societa Paleontologica Italiana 24 (2–3), 187–200. Marquet, P.A., Taper, M.L., 1998. On size and area, patterns of mammalian body size extremes across landmasses. Evolutionary Ecology 12, 127–139. Marshall, L.G., Corruccini, R.S., 1978. Variability, evolutionary rates, and allometry in dwarfing lineages. Paleobiology 4, 101–119.

ARTICLE IN PRESS M.R. Palombo / Quaternary International 169–170 (2007) 105–124 McNab, B.K., 2002. Minimizing energy expenditure facilitates vertebrate persistence on oceanic islands. Ecology Letters 5, 693–704. Meiri, S., Dayan, T., Simberloff, D., 2004. Body size of insular carnivores, little support for the island rule. American Naturalist 163, 469–479. Meiri, S., Dayan, T., Simberloff, D., 2005a. Insular carnivore biogeography: island area and mammalian optimal body size. American Naturalist 165 (4), 505–514. Meiri, S., Simberloff, D., Dayan, T., 2005b. Insular carnivore biogeography: island area and mammalian optimal body size. American Naturalist 165, 505–514. Meiri, S., Simberloff, D., Dayan, T., 2006. The generality of the island rule Re-examined. Journal of Biogeography 33, 1571–1577. Melton, R.H., 1982. Body size and island Peromyscus, a pattern and a hypothesis. Evolution Theory 6, 113–126. Mertens, R., 1934. Die Insel Reptilian. Zoologica 84, 1–205. Meyhew, D.F., 1996. The extinct murids of crete. In: Reese, D.S. (Ed.), Pleistocene and Holocene Fauna of Crete and its first Settlers. Monograph in World Archeology, vol. 28, pp. 167–171. Michaux, J.R., De Bellocq, J.G., Sara, M., Morand, S., 2002. Body size increase in insular rodent populations: a role for predators? Global Ecology and Biogeography 11, 427–436. Millien, V., 2004. Relative effects of climate change, isolation and competition on body-size evolution in the Japanese field mouse, Apodemus argenteus. Journal of Biogeography 31, 1267–1276. Millien, V., Damuth, J., 2004. Climate change and size evolution in an island rodent species: new perspectives on the island rule. Evolution 58, 1353–1360. Millien-Parra, V., Jaeger, J.-J., 1999. Island biogeography of the Japanese terrestrial mammal assemblage: an example of a relict fauna. Journal of Biogeography 26, 959–972. Mills, M.G., Moro, D., Spencer, P.B.S., 2004. Conservation significance of island versus mainland populations: a case study of dibblers (Parantechinus apicalis) in Western Australia. Animal Conservation 7, 387–395. Mol, D., de Vos, J., van den Bergh, G., Sondaar, P.Y., 1996. The taxonomy and ancestry of the fossil elephants of crete, faunal turnover and a comparison with Probpscidean faunas of Indonesian Islands. In: Reese D.S. (Ed.), Pleistocene and Holocene Fauna of Crete and its first Settlers. Monographs in World Archaeology, 28, 81–98. Morand, S., 2000. Geographic distance and the role of island area and habitat diversity in the species-area relationships of four Lesser Antillean faunal groups: a complementary note to Ricklefs and Lovette. Journal of Animal Ecology 69, 1117–1119. Morrison, L.W., 1998. The spatiotemporal dynamics of insular ant metapopulations. Ecology 79, 1135–1147. Morwood, M.J., et al., 2005. Further evidence for small-bodied hominins from the late Pleistocene of Flores, Indonesia. Nature 437, 1012. Nor, S.M., 1996. The mammalian fauna on the islands at the northern tip of Sabah, Borneo. Fieldiana-Zoology 83, 1–51. Novelli, M., Palombo, M.R., in press. ‘‘Hunter Schreger Bands’’ in Cynotherium sardous Studiati, 1857 from Dragonara cave (Late Pleistocene, North-Western Sardinia). Bollettino della Societa` Paleontologica Italiana, vol. 44. Oli, M.K., Dobson, F.S., 2003. The relative importance of life-history variables to population growth rate in mammals, Cole’s prediction revisited. American Naturalist 161 (3), 422–440. Osborn, H.F., 1942. Proboscidea. 1, 1–802. The American Museum Press, New York. Palkovacs, E.P., 2003. Explaining adaptive shifts in body size on islands, a life history approach. Oikos 103, 37–44. Palmer, M., 2002. Testing the ‘island rule’ for a tenebrionid beetle (Coleoptera, Tenebrionidae). Acta Oecolgica 23, 103–108. Palmqvist, P., Mendoza, M., Arribas, A., Grocke, D.R., 2002. Estimating the body-mass of Pleistocene canids, discussion of some methodological problems and a new ‘‘taxon free’’ approach. Lethaia 35, 358–360. Palombo, M.R., 2001. Paedomorphic features and allometric growth in Elephas falconeri skull from Spinagallo (Middle Pleistocene, Sicily). In: Cavaretta, G., Gioia, P., Muss, M., Palombo, M.R. (Eds.), The

123

World of Elephants. Consiglio Nazionale Richerche, Roma, pp. 492–496. Palombo, M.R., 2003. Elephas, Mammuthus, Loxodonta, who is the true ancestor of the dwarf elephant of Sicily? Deinsea 1999, 273–291. Palombo, M.R., 2004a. Les e´le´phants nains. Dossier d’Archeologie 291, 37–43. Palombo, M.R., 2004b. Dwarfing in insular mammals, The Endemic Elephants of Mediterranean Islands. In: Baquedano, E., Rubio, S. (Eds.), Homenaje a Emiliano Aguirre. Zona Archeologica 4 (2, Paleontologia), Museo Arqueolo´gico Regional, Madrid, pp. 354–371. Palombo, M.R., 2005a. How could endemic Proboscideans help us in understanding the ‘‘Island Rule’’? In: Proceedings of the Second International Congress on ‘‘The World of Elephants,’’ Hot Springs Mammoth Site, Hot Springs, South Dakota, USA. Palombo, M.R., 2005b. Biochronology of the Plio-Pleistocene mammalian faunas of Italian peninsula: knowledge, problems and perspectives. Il Quaternario, 17 (2004) (2/2), 565–582 Palombo, M.R., 2006. Biochronology of the Plio-Pleistocene terrestrial mammals of Sardinia: the state of the art. Hellenic Journal of Geosciences 41, 47–66. Palombo, M.R., Giovinazzo, C., 2005. Elephas falconeri from Spinagallo Cave (South-Eastern Sicily, Hyblean Plateau, Siracusa), brain to body weight comparison. In: Alcover, J.A., Bover, P. (Eds.), Proceedings of the International Symposium on ‘‘Insular Vertebrate Evolution, the Palaeontological Approach’’. Monografies de la Societat d’Histo`ria Natural de les Balears 12, 255–264. Palombo, M.R., Bover, P., Valli, A.F.M., Alcover, J.A., 2006. The PlioPleistocene endemic bovids from the Western Mediterranean islands: knowledge, problems and perspectives. Hellenic Journal of Geosciences 41, 153–162. Panero, J.L., Francisco-Ortega, J., Jansen, R.K., Santos-Guerra, A., 1999. Molecular evidence for multiple origins of woodiness and a New World biogeographic connection of the Macronesian Island endemic Percallis (Asteraceae, Senecioneae). Proceedings, National Academy of Science 96, 13886–13891. Pergams, O.R.W., Ashley, M.V., 2001. Microevolution in island rodents. Genetica 112–113, 245–256. Peters, R.H., 1983. The Ecological Implications of Body Size. Cambridge, Cambridge, UK. Pohlig, H., 1893. Eine Elephantenho¨hle Siciliens und der erste Nachweis des Cranialdomes von Elepas antiquus. Abhandlungen der Bayerische Akademie der Wissenschaften 18, 73–100. Poulakakis, N., Mylonas, M., Lymberakis, P., Fassoulas, C., 2002. Origin and taxonomy of the fossil elephants of the island of Crete (Greece), problems and perspectives. Palaeogeography, Palaeoclimatology, Palaeoecology 186, 163–183. Purvis, A., Harvey, P.H., 1997. The right size for a mammal. Nature 386, 332–333. Raia, P., Carmela, B., Conte, M., 2003. The fast life of a dwarfed giant. Evolutionary Morphology 17, 293–312. Reumer, J.W.F., 1980. On the Pleistocene shrew Nesiotites hidalgo Bate, 1944 from Majorca (Soricidae, Insectivora). Proceedings, Koninklijke Nederlandse Akademie van Wetenschappen B 83 (1), 39–68. Reumer, J.W.F., 1996. Shrews (Soricidae) on Islands, with spezial references to Crocidura zimmermanni from Crete. In: Reese, D.S. (Ed.), Pleistocene and Holocene Fauna of Crete and its first Settlers. Monographs in World Archaeology 28, 173–179. Reumer, J.W.F., Oberli, F., 1988. Shrews (Mammalia, Soricidae) from a Bronze Age deposit in Cyprus, with the description of a new subspecies. Bonner zoologische Beitra¨ge 39, 305–314. Reyment, R.A., 1983. Palaeontological aspects of island biogeography, colonization and evolution of mammals on Mediterranean islands. Oikos 41, 299–306. Robinson-Wolrath, S.I., Owens, I.P.F., 2003. Large size in an islanddwelling bird: intraspecific competition and the Dominance Hypothesis. Journal of Evolutionary Biology 16, 1106–1114. Roth, V.L., 1981. Constancy of size ratios of sympatric species. American Naturalist 118, 394–404.

ARTICLE IN PRESS 124

M.R. Palombo / Quaternary International 169–170 (2007) 105–124

Roth, V.L., 1990. Insular dwarf elephants, a case study in body-mass estimation and ecological inference. In: Damuth, J., MacFadden, B.J. (Eds.), Body Size in Mammalian Paleobiology, Estimation and Biological Implications. Cambridge University Press, Cambridge, pp. 151–179. Roth, V.L., 1992. Inferences from allometry and fossils: dwarfing of elephants on islands. Oxford Surveys in Evolutionary Biology 8, 259–288. Roth, V.L., 2001. Ecology and evolution of dwarfing in insular elephants. In: Cavaretta, G., Gioia, P., Mussi, M., Palombo, M.R. (Eds.), The World of Elephants. Consiglio Nazionale Richerche, Roma, pp. 507–509. Sander, P.M., Mateus, O., Laven, T., Knotschke, N., 2006. Bone histology indicates insular dwarfism in a new Late Jurassic sauropod dinosaur. Nature 441, 739–741. Savage, V.M., Gillooly, J.F., Woodruff, W.H., West, G.B., Allen, A.P., Enquist, B.J., Brown, J.H., 2004. The predominance of quarter-power scaling in biology. Functional Ecology 18, 257–282. Schmidt, N.M., Jensen, P.M., 2003. Changes in mammalian body length over 175 years—adaptations to a fragmented landscape? Conservation Ecology 7, 6. Schoener, T., 1969. Size patterns in West Indian Anolis lizards, I. Size and species diversity. Systematics in Zoology 18, 386–402. Scott, K.M., 1990. Postcranial dimension of ungulates as predictors of body-mass. In: Damuth, J., MacFadden, B.J. (Eds.), Body Size in Mammalian Paleobiology, Estimation and Biological Implications. Cambridge University Press, Cambridge, pp. 301–336. Scott, S.N., Clegg, S.M., Blomberg, S.P., Kikkawa, J., Owens, I.P., 2003. Morphological shifts in island-dwelling birds, the roles of generalist foraging and niche expansion. Evolution 57, 2147–2156. Shmida, A., Werger, M.J.A., 1992. Growth form diversity on the Canary Islands. Vegetation 102, 183–199. Simmons, A.H., 1999. Faunal Extinction in an Island Society: Pygmy Hippopotamus Hunters of Cyprus. Plenum, London. Sinclair, A.R.E., Mduma, S., Brashares, J.S., 2003. Patterns of predation in a diverse predator-prey system. Nature 425, 288–290. Smith, F.A., 1992. Evolution of body size among wood rats from Baja California, Mexico. Functional Ecology 6, 265–273. Sondaar, P.Y., 1977. Insularity and its effect on mammal evolution. In: Hecht, M.K., Goody, P.C., Hecht, B.M. (Eds.), Major Patterns in Vertebrate Evolution. Olenum, New York, pp. 671–707. Sondaar, P.Y., 2000. Early human exploration and exploitation on islands. Tropics 10, 203–230. Sondaar, P.Y., Boekschotten, G.J., 1967. Quaternary mammals in the South Aegean Island Arc with Notes on the other fossil mammals from the coastal regions of the Mediterranean I/II. Koninklijke Nederlandse Akademie Netensch Amsterdam, B 70 (5), 556–576. Sondaar, P.Y., Dermizakis, M.D., De Vos, J., 1996. The paleogeography and faunal evolution of the land mammals of crete. In: Reese, D.S. (Ed.), Pleistocene and Holocene Fauna of Crete and its first Settlers. Monographs in World Archaeology 28, 61–68. Spaan, A., 1996. Hippopotamus creutzburgi: the case of the Cretan Hippopotamus. In: Reese, D.S., (Ed.), Pleistocene and Holocene Fauna of Crete and its First Settlers. Monographs in World Archaeology 28, 99–110. Speakman, J.R., 2005. Body size, energy metabolism and lifespan. Journal of Experimental Biology 208, 1717–1730. Stock, C., 1935. Exiled elephants of the Channel Islands. Science Monthly 41, 205–214. Suarez, R.K., Darveau, C.-A., Childress, J.J., 2004. Metabolic scaling: a many-splendoured thing. Comparative Biochemistry and Physiology 139B, 531–541. Symeonidis, N.K., Theodorou, G., 1982. New findings of fossil elephants on Crete Island. Annales Ge´ologique des Pays Helle´niques 31, 113–129 (in Greek). Symeonidis, N.K., Theodorou, G., Gianopoulos, B., 2000. The new species Elephas chaniensis from the submerged Pleistocene deposits of

Vamos Cave at Chania, Crete. Bulletin, Society for Speleology, Greece 22, 95–108 (in Greek). Thaler, L., 1973. Nanisme et gigantisme insulaire. La Reserche 4, 741–750. Theodorou, G., 1983. The dwarf elephants of the Charkadio Cave on the island of Tilos (Dodecanese, Greece), Ph.D. dissertation, University of Athens, 231pp. Theodorou, G.E., 1986. Pleistocene elephants from Crete (Greece). Modern Geology 10, 235–242. Theodorou, G.E., 1988. Environmental factors affecting the evolution of island endemics, The Tilos exemple for Greece. Modern Geology 13, 183–188. Theodorou, G., Symeonidis, N., Stathopoulou, E., in press. Elephas tiliensis n. sp. from Tilos island (Dodecanese, Greece). Annales Ge´ologiques des Pays Helle´niques. Trevisan, L., 1949. Lo scheletro di Elephas antiquus italicus di Fonte Campanile (Viterbo). Palaeontographia Italica 44 (1948–49), 1–78. Tsoukala, E., Lister, A., 1998. Remains of straight-tusked elephant, Elephas (Paleoloxodon) antiquus Falc. and Caut. (1847) ESR-dated to oxygen isotope Stade 6 from Grevena (W. Macedonia, Greece). Bolletino della Societa Paleontologica Italiana 37, 117–139. Valverde, J.A., 1964. Remarques sur la structures et l’e´volution des communaute´s de verte´bre´s terrestres. I. Structure d’une communaute´. II. Rapport entre pre´dateurs et proies. Terre et Vie 111, 121–154. Van Valen, L.M., 1965. Morphological variation and width of ecological niche. American Naturalist 104, 589–590. Van Valen, L.M., 1973. Pattern and the balance of nature. Evolutionary Theory 1, 31–49. Van Valkenburgh, B., 1988. Trophic diversity in past and present guilds of large predatory mammals. Paleobiology 14, 155–173. Van Valkenburgh, B., 1990. Skeletal and dental predictors of body-mass in carnivores. In: Damuth, J., MacFadden, B.J. (Eds.), Body Size in Mammalian Paleobiology, Estimation and Biology Implications. Cambridge University Press, Cambridge, pp. 181–205. Vaufrey, R., 1929. Les Ele´phants nains des iles medite´rrane´ennes et la question des Isthmes Ple´istoce`ne. Archives de l’Institut de Pale´ontologie Humaine 6, 1–220. Ward, S.A., Thornton, I.W.B., 2000. Chance and determinism in the development of isolated communities. Global Ecology and Biogeography 9, 7–18. West, G.B., Brown, J.H., Enquist, B.J., 1997. A general Model for the Origin of Allometric Scaling Lows in Biology. Science 276, 122–126. West, G.B., Van Savage, M., Gillooly, J., Enquist, B.J., Woodruff, W.H., Brown., L.B., 2003. Why does metabolic rate scale with body size? Nature 421, 714. White, C.R., Seymur, R.S., 2005. Allometric scaling of mammalian metabolism. Journal of Experimental Biology 208, 1611–1619. White, T.A., Searle, J.B., 2006. Factors explaining increased body size in common shrews (Sorex araneus) on Scottish Islands. Journal of Biogeography. Whitehead, D.R., Jones, E.C., 1969. Small islands and the equilibrium theory of insular biogeography. Evolution 23, 171–179. Whittaker, R.J., 1998. Island Biogeography, Ecology, Evolution, and Conservation. Oxford University Press, Oxford. Whittaker, R.J., 2006. Island species-energy theory. Journal of Biogeography 33, 11–12. Wikelski, M., 2005. Evolution of body size in Galapagos marine iguanas. Proceedings of the Royal Society of London Series B, Biological Sciences 272, 1985–1993. Wilson, E.O., 1992. The Diversity of Life. Harvard University Press, Cambridge, MA, USA. Woofit, M., Bromham, L., 2005. Population size and molecular evolution on islands. Proceedings, Biological Science 272 (1578), 2277–2282. Zammit Maempel, G., de Bruijn, H., 1982. The Plio/Pleistocene Gliridae from the Mediterranean islands reconsidered. Proceedings, Koninklijke Nederlandse Akademie van Wetenschappen B 85, 113–128. Zelditch, M.L., Fink, W.L., 1996. Heterochrony and heterotopy, stability and innovation in the evolution of form. Paleobiology 22, 247–250.