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Long-range movements of small mammals in arid Australia: implications for land management
Journal of Arid Environments (1995) 31:441-452
L o n g - r a n g e m o v e m e n t s o f small m a m m a l s in arid Australia: i m p l i c a t i o n s for land m a n a g e m e n t
C.R. Dickman, M. Predavec & F.J. Downey
School of Biological Sciences, University of Sydney, New South Wales 2006, Australia (Received 29 April 1994, accepted 10 June 1994) This study investigated movements of seven species of small mammals at study areas in arid Western Australia and Queensland. Populations of all species fluctuated dramatically in abundance over time, with the recapture rate for individuals averaging at a low 11"3%. Mean long-distance movements ranged from 1"04 kin in the marsupial Sminthopsis hirtipes to 6-34 kin in the native rodent Pseudomys hermannsburgensis; the maximum distance recorded was 14 kin. Long-range movements occurred independently of sex, age and reproductive status in all species, but tended to increase during or after rain in the study regions. Individuals moved toward areas of rainfall, probably because rains produce local increases in food resources. We suggest that longrange movements are crucial in allowing small mammals to exploit both permanent and ephemeral refugia of increased productivity, hence facilitating long-term persistence in regional areas. Although protection of fixed refugia can be achieved by land reservation, conservation goals for small mammals and other biota will be met more realistically by improving land management throughout the arid zone with the involvement and cooperation of all land users.
©1995 Academic Press Limited
Keywords: Australia; rodents; marsupials; small mammals; rainfall; land management; movements; long-range
In~oduc~on A conspicuous feature of m a n y desert-dwelling species of vertebrates is their ability to move over long distances. In Australia, nomadic species of inland birds such as the budgerigar Mdopsirtacus undulatus m a y fly several h u n d r e d kilometres a day (Nix, 1976; Schodde, 1982); the flightless emu Dromaius novaehollandiae has been recorded to move up to 550 km in less than a year (Davies et al., 1971; Davies, 1984). Movements of 2 0 0 - 3 0 0 kin have been recorded in individual red kangaroos Macropus rufus in arid N e w South Wales (Bailey, 1971; Denny, 1982), and similar movements probably occur also in the grey kangaroo M. giganteus (Denny, 1975). In the Kalahari, wildebeest Connochaetes taurinus are one of m a n y species of highly mobile ungulates, capable of daily movements of 4 5 - 5 0 kin and longer-term movements of m a n y hundreds of kilometres (Talbot & Talbot, 1963). 0140-1963/95/040441 + 12 $12.00/0
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Although proximate factors stimulating long-range movements are poorly known, it is usually assumed that organisms benefit from such movements by gaining access to improved food or water supplies (Schodde, 1982). Rapid movements of birds toward areas of local rainfall or flooding suggest direct responses to water (Frith, 1959, 1962), whereas delayed movements are more suggestive of responses to rain-induced flushes of food (Schodde, 1982). Among ungulates, transient movements of several ldlometres occur in. response to local rainfall or fresh green plant growth (Bothrna, 1972; Ghobrial, 1974), whereas longer-range movements follow traditional routes toward permanent water (Williamson & Williamson, 1985). Movements of 10-25 krn have been recorded in many species of herbivores toward ephemeral patches of green food (e.g. Newsome, 1965; McCullough, 1985; Croft, 1991), and in carnivores toward temporary aggregations of prey (Skinner & Smithers, 1990). Although increased access to resources is the most obvious benefit for migrants, Fryxell et al. (1988) have argued that migration in some ungulates also reduces the effects of sedentary predators. In contrast to the wealth of observations on birds and large mammals, there is scant evidence that long-range movements occur in desert-dwelling small mammals. In North America, for example, individuals of most species that have been studied appear to occupy discrete home ranges or territories (Jones, 1993; Randall, 1993). Maximum movements are associated with either juvenile dispersal (Jones, 1987; Lidicker & Patton, 1987) or dispersal of adults (Zeng & Brown, 1987; Brown & Zeng, 1989), but very seldom exceed 1 krn. Similar findings have been obtained for species of arid regions in southern Africa (Skinner & Smithers, 1990) and South America (Redford & Eisenberg, 1992). In Australia, however, anecdotal reports (e.g. Plomley, 1972) and incidental records (Read, 1984) of long-range movements suggest that small desert mammals may be more mobile than has been suspected previously. Such observations have implications for understanding the general ecology and minimum area requirements of small mammals. This understanding is particularly important in arid Australia, where rodents and small marsupials have suffered a high rate of extinction since European colonization (Burbidge & McKenzie, 1989; Morton, 1990; Dickman et al., 1993a), and where effective conservation of remaining species may depend on protection of large enough areas to maintain viable populations. In the present study, we (1) describe patterns of long-range movements of small mammals at two study areas in arid Australia, (2) relate movements to rainfall events, and (3) comment on the implications of our findings for land reservation and management.
Study areas
Data were collected from two study areas as part of broader studies on the ecology of terrestrial vertebrates. The first area is centred N 20 km north-east of Bulgalbin Hill in the western goldfields of Western Australia (30°16'S, 119°46'E). This area is an undulating yellow sand plain dominated by tall shrubs (Acacia coolgardiensis, Banksia elderana) and stands of mallee (Eucalyptus leptopoda), with a patchy ground cover of hummock grass (Plecrrachne sp.) and low perennial shrubs (Grevillea spp., Daviesia hakeoides, Calytrix cresswellii, Pachynema junceum and Melaleuca spp.) (Newbey & I-inatiuk, 1985). Rainfall averages 265 mm a year. The second study area is centred 15 km north of Ethabuka Station homestead on the eastern edge of the Simpson Desert, Queensland (23°46'S, 138°28'E). This area is characterized by long red sand dunes up to 8 m high that run south to north in line with the prevailing southerly winds (Twidale & Wopfiaer, 1990). Low trees (Acacia cambage0 occur in the dune swales. Hummock grass (Triodia basedowiz) dominates the ground level vegetation, with a scattering of low perennial shrubs (Crotalaria sp., Enchylaena tomentosa, Sclerolaena diacantha) occurring
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f r o m the dune sides to the crests. Rainfall is probably between 165 m m and 264 m m a year, as judged f r o m records of the nearest weather stations 245 k m to the south-east and 180 k m to the north-east, respectively (Bureau of Meteorology, 1988).
Methods Animals were live-captured using pitfall traps (16 c m wide and 5 0 - 6 0 cm deep) equipped with a 5 m drift fence of a l u m i n i u m flywire to enhance trap efficiency (Friend et al., 1989). In Western Australia, 12 × 0-6 ha grids of 30 pitfall traps were set 0-4-2-0 k m apart along an access track running in a roughly north-easterly direction, with the furthest grids being ~ 10 k m apart. In Queensland, 21 × 1.0 ha grids of 36 pitfall traps were set 0.5-2-0 k m apart running in a northerly direction, with the furthest being 14 k m apart. In b o t h study areas traps were checked once or twice a day for 2-7 consecutive days a b o u t once every 2 months. C a p t u r e d animals were weighed, sexed, checked for reproductive condition and given a unique m a r k by toe or ear clipping. M o v e m e n t s were recorded by measuring linear distances between recaptures. We define short-range m o v e m e n t s as distances m o v e d within grids ( < 100 m) and long-range m o v e m e n t s as distances m o v e d between them. T r a p p i n g was carried out at Bungalbin Hill between N o v e m b e r 1987 and M a y 1989, and in the Simpson Desert between M a r c h 1990 and July 1993. T o t a l trapping effort ( n u m b e r of traps set × n u m b e r of nights open) was 57,300 trap nights. T o investigate possible effects of rain, we c o m p a r e d distances m o v e d between grids by small m a m m a l s during dry periods with m o v e m e n t s that occurred during periods of rain or within a m o n t h of rain having fallen in the study regions. Detailed records of rainfall were available f r o m a rain gauge at the Bungalbin Hill study area, and f r o m a gauge at Ethabuka Station h o m e s t e a d 15 k m south of the study area in the Simpson Desert. Further qualitative records of rainfall were m a d e by noting the presence of standing water at the study areas and on tracks leading to and f r o m them.
Results
Capture statistics Eleven species of small m a m m a l s were captured at Bungalbin Hill and 13 in the Simpson Desert, six species were found at b o t h study areas (Table 1). Species differed dramatically in a b u n d a n c e within areas. T h e m o r e c o m m o n species in each area were represented by hundreds of individuals over the course of the study, whereas at the opposite extreme the dasyurid marsupial Sminthopsis macroura was represented by only two captures over three years in the Simpson Desert and the h o p p i n g - m o u s e Notomys alexis was recorded twice at Bungalbin Hill. Rodents p r e d o m i n a t e d in b o t h areas. Individuals were recaptured relatively infrequently (Table 1); the m e a n recapture rate across all species was 11-3%, ranging f r o m 6.8% in Pseudomys hermannsburgensis to 73-8% in Sminthopsis hirtipes. Just u n d e r half of all recaptures (44.8%, n = 223) occurred within trapping sessions, with very few (1.2%, n = 6) occurring a year or m o r e later. Population sizes of the m o r e c o m m o n species, represented simply by n u m b e r s of captures, fluctuated greatly between trapping sessions (Table 1). T h e s e large numerical fluctuations and the low recapture rates suggest that individuals are highly mobile and populations transient over short periods.
C. R. DICKMAN E T A L .
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SMALLMAMMALMOVEMENTS IN ARID AUSTRALIA
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Movements Most individuals were recaptured on the grid of their initial capture, but small numbers moved between grids for distances up to 14 km (Fig. 1). Movements within trapping sessions were predominantly short-range, accounting for 91.5% (n = 204) of all movements within sessions. Within-session short-range movements varied from 78.8% of recaptures in P. albocinereus to 97.7% in P. hermannsburgensis. T h e r e was no clear tendency for long-range movements to increase over time. Distance moved was weakly correlated with n u m b e r of months between captures in N. alexis (r = + 0.41, p = 0-05), but not in any other species (r values ranged from + 0.03 to + 0-47, p = NS). T h e total n u m b e r of long-range movements in all species (n = 99) represented 19.9% of the movements recorded (n = 498). T h e occurrence of longrange movements was similar in rodents (18.8%) and dasyurids (24.0%); long-range m o v e m e n t was most prevalent in P. albocinereus (44.0%) and least in R. villosissimus (2.99%). Rodents generally moved further than marsupials, with 10 of the 14 longest ( > 10 kin) movements being made by P. hermannsburgensis, three by N. alexis, and only one movement, of 12 km, by S. youngsoni (Fig. 1). Excluding recaptures within grids, mean distances moved ranged from 1.04 km in Sminthopsis hirtipes to 6.34 km in P. hermannsburgensis. T h e occurrence of long-range movements differed between species of similar mean body mass, such as N. alexis and P. albocinereus, or S. hirtipes and S. dolichura, thus providing no indication that distance moved is related to body size (cf. Fig. 1 and Table 1). Within each species, movements between grids were made by both sexes, by juveniles and by breeding and non-breeding adults. T o determine whether any class of animals within each species population was more or less likely to move, we compared the proportions of individuals in all sex/age categories moving between grids over the course of the study, with the proportions in the same categories in the populations. N o test results were significant (X2 < 3.84, 1 dr., p > 0.05 for all tests, using correction for
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<0.10 0 . 1 0 - 0.50- 1 . 0 0 - - 2 . 0 0 - 3 . 0 0 - 4 . 0 0 - 5 . 0 0 - >~10 0.49 0.99 1.99 2.99 3.99 4.99 9.99
Distance moved (kin)
Figure 1. Distances moved by six species of small mammals in two study areas in arid Australia, (a) Bungalbin Hill in Western Australia and (b) Ethabuka Station in Queensland. Movements are defined as recaptures within trapping grids (<0.1 kin) or between grids (a 0.1 km), and numbers of movements are shown as log (x + 1). Two movements by Rattus villosissirnus of 0"75 and 2.05 km are not shown. The absence of recaptures at distances of 0.10-0.49 km at Ethabuka Station reflects the lack of trapping grids in this distance class. (a) [] = Pseudomys albodnereus; • = Sminthopsis hirtipes; [] = Sminthopsis dolichura. (b) [] = Pseudomys hermannsburgensis; [] = Notomys alexis; [] = Sminthopsis youngsoni.
C. R. DICKMANETAL.
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Table 2. Long-distance (between-grid) movements of smodl mammals at.two
study areas in arid Australia in relation w rainfall Distance moved, km +- S.D. (n) During dry periods
During or after rain
t
p
1-42+1.40(13) 0.76+-0.34(7) 2.90+2.72(4)
2.86+-2.84(9) 1.32+_0-67(7) 4-20(1)
1.66 2.00 --
NS NS --
5.63+5"57(11) 1-38+0.88(11) 1.40+_0.92(2) 0-96+_0.34(4)
6-82+4"86(16) 5.45+5-42(12) -7"25+_6"72(2)
0"36 2.45 -2.15
NS <0.05 -NS
Bungalbin Hill, W.A.
Pseudomys albocinereus Sminthopsis hirtipes Sminthopsis dolichura Simpson Desert, Queensland Pseudomys hermannsburgensis Nowmys alexis Ratrus villosissimus Sminthopsis youngsoni NS = not significantat a = 0.05.
continuity), suggesting that neither sex nor age nor reproductive status predispose individuals to move. Inspection of the raw capture data indicated that long-range movements occurred at all times of year, but appeared to be associated particularly with periods of rainfall. Movements ranged from being 21.1% greater during or after rainfall than during dry periods for Pseudomys hermannsburgensis, to 6.5-fold greater in Sminthopsis youngsoni, with an average increase across all species of almost 200% (Table 2). Increased movement was statistically significant only in Notomys alexis, but approached significance (0.1 > p > 0.05) in Sminthopsis hirtipes and S. youngsoni. Sixteen of 47 long-distance movements occurred during or after rain on the study areas, whereas 31 movements occurred within a m o n t h of rain that fell up to 15 krn away from the grids. O f these latter movements, 23 (74.2%) were in a northerly or southerly direction toward the area of rainfall. This orientation toward rain is significant (X2co~ = 6.32, p < 0-05), if it is assumed that there is an equal probability of movement toward or away from precipitation.
Discussion
Long-range movements T h e maximum distances moved by small mammals in this study generally exceed those reported elsewhere in Australia. In semi-arid grassland in New South Wales, for example, Read (1984) noted an exceptional movement by Sminthopsis crassicaudata of 5 km and a maximum movement by Planigale gilesi of 1"3 km. Ram~s villosissimus may be more mobile, with distances of - 3 km being covered per day during plagues (Finlayson, 1939), but movements by marked individuals have been little studied (Prevadec & Dickman, 1994). Movements of small mammals in temperate and tropical parts of Australia appear to be particularly limited, with distances of > 1 km being seldom recorded (e.g. Wood, 1970, 1971; Smith, 1984; Leung et al., 1993). In part, the appearance of limited movement in previous studies may be due to use of relatively small sampling areas that reduce the chance of long-range recaptures, and infrequent use of alternative methods such as radio-telemetry. However, observations of homing behaviour (Fox & Cooper, 1982) and studies using a similar dispersion of
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grids to that in the present work (Dickman, 1980, 1986) suggest that lifetime movements of small mammals in non-arid Australian environments seldom exceed 2-3 km. There is little evidence of greater mobility of small mammals either in temperate environments outside Australia (e.g. Kirkland, 1988; Dickman & Doncaster, 1989), or in other world deserts (e.g. Brown & Zeng, 1989; Ascaray & McLachlan, 1990). Although we recorded several individuals moving up to 14 km, the true magnitude of long-distance movements within species populations was probably much greater than the records suggest. In the first instance, the nearly linear disposition of the trapping grids ensured that only those animals moving in northerly or southerly directions would have been at risk of capture. If movements occur equally in all directions, our grids would have intercepted < 5% of all dispersers. Secondly, the rate of recapture for all species was relatively low, within and between field trips, whereas the rate of appearance of new individuals was high. Similarly high rates of population turnover have been reported for small mammals elsewhere in arid Australia (Dunlop & Sawle, 1982; Masters, 1993), and may characterize species with unstable, drifting 'home ranges' (Morton, 1978; Read, 1984). The factors that promote long-range movements of arid-zone small mammals cannot be specified precisely, but several observations suggest that rainfall may be important. Firstly, movements tended to increase after rain, and were directed toward areas where rain had fallen. Secondly, populations of rodents increased locally on both study areas after rain, suggesting that immigrants had moved from surrounding areas. At Bungalbin Hill, numbers of P. albocinereus were 82% higher in November and December 1988 (n = 40) less than six weeks after rain had fallen, than during the same period in 1987 (n = 22) when conditions were dry. T h e increase in 1988 was due entirely to immigration because the time from conception to weaning in P. albocinereus is too long (73-74 days; Watts, 1982) to have allowed population increase via reproduction. In the Simpson Desert, Predavec (1994) described dramatic increases in numbers of P. hermannsburgensis and N. alexis after rain; the relative contributions of immigration and in situ reproduction to the population increases are unclear, but some movement is probably involved. Finally, we recorded an extension of range of the hairy-footed dunnart Sminthopsis hirtipes into the eastern Simpson Desert in 1992; this appeared to be due to long-range movements of individuals following unusually heavy rainfall (Dickman et aL, 1993b). Rain may be used most obviously as a source of free water by small mammals, but it is probably still more important in increasing food resources. For rodents, rain may produce an immediate increase in food by enhancing the accessibility of bu0.'ed seeds. Johnson & Jorgensen (1981) showed that several species of rodents in North American deserts find more seeds buried in moist than in dry sand, apparently because moistened seeds provide relatively strong olfactory cues. Vander Wall (1993) demonstrated further that hydrated seeds are more vulnerable to foragers than dry seeds when buried in dry sand. Rain may also have longer-term effects by promoting plant growth. Th e rodents we studied are omnivorous and eat the green stem, leaf material and fungi, as well as seeds, that become more abundant after rain (Murray & Dickman, 1994), whereas dasyurids are broadly insectivorous and may utilize increased invertebrate populations (Fisher & Dickman, 1993). Movements from drought-affected areas with diminished resources to resource-rich sites may thus be advantageous, providing fitness benefits to individuals that move. In contrast, nonmovement may represent a particularly risky strategy for individuals living in an impoverished area. Spatial and temporal predictability of local rainfall is very low in arid Australia (Gentilli, 1972; Fleming, 1978); hence sedentary individuals should face considerable uncertainty that conditions will improve in a local area within their lifetime. In arid areas outside Australia, more reliable rainfall may allow greater or more
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continuous production of food resources for small mammals, and minimize any benefits of long-range movement. Further, caching of food, which has been described in a wide variety of desert-dwelling cricetid and heteromyid rodents (de Graaf, 1981; Downs & Perrin, 1989; Randall, 1993; Reichman & Price, 1993), probably provides a buffer against temporary food shortage. There is little evidence that similar behaviour is exhibited by either rodents or dasyurids in arid Australia (Watts & Aslin, 1981; cf. Baker et M., 1993). Physiological adaptations that temporarily reduce demand for food, such as facultative heterothermy, are also prevalent in heteromyids (French, 1993). Only P. herrnannsburgensis in arid Australia is suspected to be able to enter torpor (Predavec, 1994). The importance of drought-refuge sites has been documented for many species of terrestrial vertebrates in arid Australia (Finlayson, 1943; Watts & Aslin, 1974), and the concept of shifting refugia has been recognized explicitly by Newsome & Corbett (1975). Morton (1990) has proposed further that the recent degradation of refuge sites by introduced herbivores in arid Australia has contributed to losses of medium-sized mammals, whereas smaller species (< 35 g) have persisted because their resource requirements can be met in smaller, disturbed patches. Our results suggest that persistence of small mammals may be facilitated also by their extraordinary mobility, which should allow colonization of transient patches regenerating after rain even if these are scattered widely over the desert landscape. Long-distance movement should be especially important if rain falls on drought-struck areas containing in situ populations too low to respond quickly to resource pulses. These conclusions accord with theoretical predictions that the persistence of populations at the regional level will be increased by asynchronous fluctuations among constituent local populations; if any one local population disappears, recolonization by migrants will prevent extinction of the whole (Allen et al., 1993).
Implications for conservation and land management
For long-term conservation of add-zone small mammals, and other biota, it is clear that land must be managed to protect not only permanent oases (Morton, 1990), b u t also the ephemeral refugia of increased productivity that appear after local rains and disappear during droughts. Because they are fixed, permanent refugia such as oases and riverine strips can be identified readily and protected by means such as land reservation. Systematic methods of reserve selection are available for such refugia (e.g. Pressey & Nicholls, 1989a, b, 1991), and an hierarchical system of land uses has been proposed that would focus management on the most critical sites (Morton et al.,
1995). In contrast, ephemeral refugia are not spatially predictable and could be expected to occur frequently outside of reserved land. These could be colonized by small mammals only if the non-reserved land surrounding them was traversable. Land use in arid Australia is dominated by the pastoral industry, but substantial areas are used also for resource exploration, mining and tourism; much of this land is degraded and of poor quality for small mammals (Stanley, 1983; Dickman, 1993). An approach to protecting ephemeral land patches and the small mammals and other biota that use them is to aim for improved land management outside national parks and other reserves. This approach recognizes the practical reality that a large and fully representative reserve system may be difficult to achieve in arid Australia, and also that reserves will be more effective if they are not embedded in a hostile landscape (Schonewald-Cox & Bayless, 1986). Conservation goals will clearly be difficult to achieve without the full cooperation of all land users and local communities. In South Australia, a cooperative approach is being pioneered toward ecologically sustainable land care in large, multiple-use regional reserves, with conservation remaining as the
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major objective (Cohen, 1990, 1992). M o r e generally, M o r t o n et al. (1995) have emphasized the importance of seeking c o m m o n , regional stewardship in arid Australia, and offer a practical structure for identifying and managing different categories of sustainable land uses. We agree with this holistic view, and believe that appropriate regional scale m a n a g e m e n t will be crucial for conservation of mobile organisms, such as small mammals, which have m u c h larger area requirements than have been appreciated hitherto. We thank the many volunteers who assisted at different times with fieldwork, especially H. Braak, H. Brurmer, J. Richards and P.C. Withers. We also thank D. and P. Smith for their hospitality and access to Ethabuka Station, and R.P. Kavanagh, and M.B. Thompson for commenting critically on the manuscript. The research was supported by grants from the Australian Research Council (to CRD) and the Australian Geographical Society, Australian Museum Postgraduate Grant Scheme and Ethel Mary Read Fund of The Royal Zoological Society of New South Wales (to M.P).
References Allen, J.C., Schaffer, W.M. & Rosko, D. (1993). Chaos reduces species extinction by amplifying local population noise. Nature, 364: 229-232. Ascaray, C.M. & McLachlan, A. (1990). Home range of Gerbilluruspaeba in a southern African coastal dunefield. Zeitschriftfiir Saugetierkunde, 55: 399-406. Bailey, P.T. (1971). The red kangaroo, Megaleia tufa (Desmarest), in north-western New South Wales. CSIRO Wildlife Research, 16:11-28. Baker, L., Woenne-Green, S. & the Mutitjulu Community (1993). An_angu knowledge of vertebrates and the environment. In: Reid, J.R.W., Kerle, J.A. & Morton, S.R. (Eds), Kowari 4: Uluru Fauna, pp.79-132. Canberra: Australian National Parks and Wildlife Service. 152 pp. Bothma, J. du P. (1972). Short-term response in ungulate numbers to rainfall in the Nossob River of the Kalahari Gemsbok National Park. Koedoe, 15: 127-133. Brown, J.H. & Zeng, Z. (1989). Comparative population ecology of eleven species of rodents in the Chihuahuan Desert. Ecology, 70: 1507-1525. Burbidge, A.A. & McKenzie, N.L. (1989). Patterns in the modem decline of Western Australia's vertebrate fauna: causes and conservation implications. BiologicalConservation, 50: 143-198. Bureau of Meteorology. (1988). Climatic Averages Australia. Canberra: Australian Government Publishing Service. 532 pp. Cohen, B. (1990). Reconstruction of South Australia's arid lands: the conservation option. Proceedings of the Ecological Society of Australia, 16: 459-465. Cohen, B. (1992). Multiple use and nature conservation in South Australia's arid zone. Rangeland ffournal, 14:205-214. Croft, D.B. (1991). Home range of the red kangaroo Macropus rufus, ffournal of Arid Environments, 20: 83-98. Davies, S.J.J.F. (1984). Nomadism as a response to desert conditions in Australia. ffournal of Arid Environments, 7: 183-195. Davies, S.J.J.F., Beck, M.W.R. & Kruiskamp, J.P. (1971). The results of banding 154 emus in Western Australia. CSIRO Wildlife Research, 16: 77-79. de Graaff, G. (1981). The Rodents of Southern Africa. Durban: Butterworths. 267 pp. Denny, M.J.S. (1975). The occurrence of the eastern grey kangaroo west of the Darling River. Search, 6; 89-90. Denny, M.J.S. (1982). Adaptations of the red kangaroo and euro (Macropodidae) to aridity. In: Barker, W.R. & Greenslade, P.J.M. ('Eds), Evolution of the Flora and Fauna of Arid Australia, pp. 179-183. Frewville: Peacock Publications. 392 pp. Dickrnan, C.R. (1980). Ecological studies of Antechinus stuartii and Antechinus flavipes (Marsupialia: Dasyuridae) in open-forest and woodland habitats. Australian Zoologist, 20: 433-446. Dickrnan, C.R. (1986). Niche compression: two tests of an hypothesis using narrowly sympatric predator species. Australian ffournal of Ecology, 11: 121-134.
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C. P,. DICKMANETAL.
Dickman, C.R. (1993). The biology and management of native rodents of the arid zone in N.S.W. New South Wales National Parks and Wildlife Service Species Management Report, 12: 1-149. Dickman, C.R. & Doncaster, C.P. (1989). The ecology of small mammals in urban habitats. II. Demography and dispersal, ffournal of Animal Ecology, 58:119-127. Dickrnan, C.R., Pressey, R.L., Lira, L. & Pamaby~ H.E. (1993a). Mammals of particular conservation concern in the Western Division of New South Wales. Biological Conservation, 65: 219-248. Dickman, C.R., Downey, F.J. & Predavec, M. (1993b). The hairy-footed dunnart Sminthopsis hirtipes (Marsupialia: Dasyuridae) in Queensland. Australian Mammalogy, 16: 69-72. Downs, C.T. & Perrin, M.R. (1989). An investigation of the macro- and micro- environments of four Gerbillurus species. Cimbebasia, 11: 41-54. Dunlop, J.N. & Sawle, M. (1982). The habitat and life history of the Pilbara ningaui Ningaui timealeyi. Records of the Western Australian Museum, 10: 47-52. Firdayson, H.H. (1939). On mammals from the Lake Eyre basin. Part V. General remarks on the increase of murids and their population movements in the Lake Eyre basin during the years 1930-1936. Transactions of the Royal Society of South Australia, 63: 348-353. Finlayson, H.H. (1943). The Red Centre. Sydney: Angus & Robertson. 153 pp. Fisher, D.O. & Dicknaan, C.R. (1993). Diets of insectivorous marsupials in arid Australia: selection for prey type, size, or hardness? Journal of Arid Environments, 25: 397-410. Fleming, P.M. (1978). Types of rainfall and local rainfall variability. In: Howes, K.M.W. (Ed.), Studies of the Australian Arid Zone. Part 111. Water in rangelands, pp. 18-28. Melbourne: CSIRO. 225 pp. Fox, B.J. & Cooper, W.T. (1982). Homing in Antechinus stuartii (Marsupialia: Dasyuridae). Australian Mammalogy, 5:71-73. French, A.R. (1993). Physiological ecology of the Heteromyidae: economics of energy and water utilization. In: Genoways, H.H. & Brown, J.H. (Eds), Biology of the Heteromyidae, pp. 509-538. The American Society of Marnmalogists. 719 pp. Friend, G.R., Smith, G.T., Mitchell, D.S. & Dickman, C.R. (1989). Influence of pitfall and drift fence design on capture rates of small vertebrates in semi-arid habitats of Western Australia. Australian Wildlife Research, 16: 1-10. Frith, H.J. (1959). The ecology of wild ducks in inland New South Wales II. Movements. CSIRO Wildlife Research, 4: 108-130. Frith, H.J. (1962). Movements of the grey teal, Anas gibberffrons Muller (Anatidae). CSIRO Wildlife Research, 7: 50-70. Fryxell, J.M., Greever, J. & Sinclair, A.R.E. (1988). Why are migratory ungulates so abundant? American Naturalist, 131: 781-798. Genfilli, J. (1972). Australian Climate Patterns. Melbourne: Nelson. 285 pp. Ghobrial, L.I. (1974). Water relation and requirement of the dorcas gazelle in the Sudan. Mammalia, 38: 88-107. Johnson, T.K. & Jorgensen, C.D. (1981). Ability of desert rodents to find buried seeds. Journal of Range Management, 34:312-314. Jones, W.T. (1987). Dispersal patterns in kangaroo rats Dipodomys spectabilis. In: Chepko-Sade, B.D. & Halpin, Z.T. (Eds), Mammalian Dispersal Patterns, pp. 119-127. Chicago: University of Chicago Press. 342 pp. Jones, W.T. (1993). The social systems of heteromyid rodents. In: Genoways, H.H. & Browne J.H. (Eds), Biology of the Heteromyidae, pp.575-595. The American Society of Mammalogists. 719 pp. Kirldand, G.L., Jr. (1988). Meadow voles Microtuspennsylvanicus on forest clearcuts: the role of long-distance dispersal. Journal of the Pennsylvania Academy of Science, 62: 83-85. Leung, L.K.-P., Dickrnan, C.R. & Moore, L.A. (1993). Genetic variation in fragmented populations of an Australian rain.forest rodent, Melomys cervinipes. Pacific Conservation Biology, 1: 58-65. Lidicker, W.Z., Jr. & Patton, J.L. (1987). Patterns of dispersal and genetic structure in populations of small rodents. In: Chepko-Sade, B.D. & Halpin, Z.T. (Eds), Mammalian Dispersal Patterns, pp. 144-161. Chicago: University of Chicago Press. 342 pp. Masters, P. (1993). The effects of fire-driven succession and rainfall on small mammals in spinifex grassland at Uluru National Parks Northern Territory. Wildlife Research, 20: 803-813.
SMALLMAMMALMOVEMENTSIN ARIDAUSTRAJ_JA
451
McCullough, D.R. (1985). Long range movements of large terrestrial mammals. Contributions in Marine Science, 27 (Supplement): 44~ ~65. Morton, S.R. (1978). An ecological study ofSminthopsis crassicaudata (Marsupialia: Dasyuridae) II. Behaviour and social organization. Australian Wildlife Research, 5: 163-182. Morton, S.R. (1990). The impact of European settlement on the vertebrate animals of arid Australia: a conceptual model. Proceedings of the Ecological Society of Australia, 16: 201-213. Morton, S.R., Stafford Smith, D.M., Friedel, M.H., Griffin, G.F. & Pickup, G. (1995). The stewardship of arid Australia: ecology and landscape management. Journal of Environmental Management (in press). Murray, B.R. & Dickman, C.R. (1994). Granivory and microhabitat use in Australian desert rodents: are seeds important? Oecologia, 99: 216-225. Newbey, K.R. & Hnatiuk, R.J. (1985). Vegetation and flora. Records of the Western Australian Museum, 23 (Suppl.): 11-38. Newsome, A.E. (1965). The distribution of red kangaroos about sources of persistent food and water in central Australia. Australian Journal of Zoology, 13: 289-299. Newsome, A.E. & Corbett, L.K. (1975). Outbreaks of rodents in semi-arid and arid Australia: causes, preventions, and evolutionary considerations. In: Prakash, I. & Ghosh, P.K. (Eds), Rodents in Desert Environments, pp. 117-153. The Hague: Junk. 624 pp. Nix, H.A. (1976). Environmental control of breeding, post-breeding dispersal and migration of birds in the Australian region. In: Frith, H.J. & Calaby, J.H. (Eds), Proceedings of the 16th International Ornithological Congress, pp. 272-305. Canberra: Australian Academy of Science. 765 pp. Plomley, N.J.B. (1972). Some notes on plagues of small mammals in Australia. Journal of Natural History, 6: 363-384. Predavec, M. (1994). Food limitation and demography in Australian desert rodents. Ph.D. thesis, University of Sydney, Sydney. Predavec, M. & Dickman, C.R. (1994). Population dynamics and habitat use of the long-haired rat (Rattus villosissimus) in south-western Queensland. Wildlife Research, 21:1-10. Pressey, R.L. & Nicholls, A.O. (1989a). Efficiency in conservation evaluation: scoring versus iterative approaches. Biological Conservation, 50 199-218. Pressey, R.L. & Nicholls, A.O. (1989b). Application of a numerical algorithm to the selection of reserves in semi-arid New South Wales. Biological Conservation, 50: 263-278. Pressey, R.L. & Nicholls, A.O. (1991). Reserve selection in the Western Division of New South Wales: development of a new procedure based on land system mapping. In: Margules, C.R. & Austin, M.P. (Eds), Nature Conservation: Cost effective biologicalsurveys and data analysis, pp. 98-105. Melbourne: CSIRO. 207 pp. Randall, J.A. (1993). Behavioural adaptations of desert rodents (Heteromyidae). Animal Behaviour, 45: 263-287. Read, D.G. (1984). Movements and home ranges of three sympatric dasyurids, Sminthopsis crassicaudata, Planigale gilesi and P. tenuirostris (Marsupialia), in semiarid western New South Wales. Australian Wildlife Research, 11: 223-234. Redford~ K.H. & Eisenberg, ~[.F. (1992). Mammals of the Neotropics: The southern cone. Chicago: University of Chicago Press. 430 pp. Reichman, O.J. & Price, M.V. (1993). Ecological aspects ofheteromyid foraging. In: Genoways, H.H. & Brown, J.H. (Eds), Biology of the Heteromyidae, pp. 539-57.4. The American Society of Mammalogists. 719 pp. Schodde, R. (1982). Origin, adaptation and evolution of birds in arid Australia. In: Barker, W.R. & Greenslade, P.J.M. (Eds), Evolution of the Flora and Fauna of Arid Australia, pp. 191-224. Frewville: Peacock Publications. 392 pp. Schonewald-Cox, C.M. & Bayless, J.W. (1986). The boundary model: a geographical analysis of design and conservation of nature reserves. Biological Conservation, 38: 305-322. Skinner, J.D. & Smithers, R.H.N. (1990). The Mammals of the Southern Aft'can Subregion. Pretoria: University of Pretoria. 771 pp. Smith, G.C. (1984). The biology of the yellow-footed antechinus, Antechinus flavipes (Marsupialia: Dasyuridae), in a swamp forest on Kinaba Island, Cooloola, Queensland. Australian Wildlife Research, 11: 465480. Stanley, R.J. (1983). Soils and vegetation: an assessment of current status. In: Messer, J. & Mosley, G. (Eds), What Future for Australia's Arid Lands? pp. 8-18. Hawthorn: Australian Conservation Foundation. 206 pp.
452
C.R. DICKMANETAL
Talbot, L.M. & Talbot, M.H. (1963). The wildebeest in western Masailand, East Africa. Wildlife Monographs, 12: 1-88. Twidale, C.R. & Wopfiaer, H. (1990). Dune fields. In: Tyler, M.J., Twidale, C.R., Davies, M. & Wells, C.B. (Eds), Natural History of the North East Deserts, pp. 45-60. Adelaide: Royal Society of South Australia. 226 pp. Vander Wall, S.B. (1993). Seed water content and the vulnerability of buried seeds to foraging rodents. American Midland Naturalist, 129:272-281. Watts, C.H.S. (1982). Australian hyclromyine rodents: maintenance of captive colonies. In: Evans, D.D. (Ed.), The Management of Australian Mammals in Captivity, pp. 180-184. Melbourne: Zoological Board of Victoria. 188 pp. Watts, C.H.S. & Aslin, H.J. (1974). Notes on the small mammals of north-eastern South Australia and south-western Queensland. Transactions of the Royal Society of South Australia, 98: 61-69. Watts, C.H.S. & Aslin, H.J. (1981). The Rodents of Australia. Sydney: Angus & Robertson. 321 pp. Williamson, D. & Williamson, J. (1985). Botswana's fences and the depletion of Kalahafi wildlife. Parks, 10: 5-7. Wood, D.H. (1970). An ecological study of Antechinus stuartii (Marsupialia) in a south-east Queensland rain forest. Australian Journal of Zoology, 18: 185-207. Wood, D.H. (1971). The ecology of Rartus fuscipes and Melomys cervinipes (Rodentia: Muridae) in a south-east Queensland rain forest. Australian Journal of Zoology, 19:371-392. Zeng, Z. & Brown, J.H. (1987). Population ecology of a desert rodent: Dipodomys merriami in the Chihuahuan Desert. Ecology, 68: 1328-1340.
L o n g - r a n g e m o v e m e n t s o f small m a m m a l s in arid Australia: i m p l i c a t i o n s for land m a n a g e m e n t
C.R. Dickman, M. Predavec & F.J. Downey
School of Biological Sciences, University of Sydney, New South Wales 2006, Australia (Received 29 April 1994, accepted 10 June 1994) This study investigated movements of seven species of small mammals at study areas in arid Western Australia and Queensland. Populations of all species fluctuated dramatically in abundance over time, with the recapture rate for individuals averaging at a low 11"3%. Mean long-distance movements ranged from 1"04 kin in the marsupial Sminthopsis hirtipes to 6-34 kin in the native rodent Pseudomys hermannsburgensis; the maximum distance recorded was 14 kin. Long-range movements occurred independently of sex, age and reproductive status in all species, but tended to increase during or after rain in the study regions. Individuals moved toward areas of rainfall, probably because rains produce local increases in food resources. We suggest that longrange movements are crucial in allowing small mammals to exploit both permanent and ephemeral refugia of increased productivity, hence facilitating long-term persistence in regional areas. Although protection of fixed refugia can be achieved by land reservation, conservation goals for small mammals and other biota will be met more realistically by improving land management throughout the arid zone with the involvement and cooperation of all land users.
©1995 Academic Press Limited
Keywords: Australia; rodents; marsupials; small mammals; rainfall; land management; movements; long-range
In~oduc~on A conspicuous feature of m a n y desert-dwelling species of vertebrates is their ability to move over long distances. In Australia, nomadic species of inland birds such as the budgerigar Mdopsirtacus undulatus m a y fly several h u n d r e d kilometres a day (Nix, 1976; Schodde, 1982); the flightless emu Dromaius novaehollandiae has been recorded to move up to 550 km in less than a year (Davies et al., 1971; Davies, 1984). Movements of 2 0 0 - 3 0 0 kin have been recorded in individual red kangaroos Macropus rufus in arid N e w South Wales (Bailey, 1971; Denny, 1982), and similar movements probably occur also in the grey kangaroo M. giganteus (Denny, 1975). In the Kalahari, wildebeest Connochaetes taurinus are one of m a n y species of highly mobile ungulates, capable of daily movements of 4 5 - 5 0 kin and longer-term movements of m a n y hundreds of kilometres (Talbot & Talbot, 1963). 0140-1963/95/040441 + 12 $12.00/0
© 1995 Academic Press Limited
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Although proximate factors stimulating long-range movements are poorly known, it is usually assumed that organisms benefit from such movements by gaining access to improved food or water supplies (Schodde, 1982). Rapid movements of birds toward areas of local rainfall or flooding suggest direct responses to water (Frith, 1959, 1962), whereas delayed movements are more suggestive of responses to rain-induced flushes of food (Schodde, 1982). Among ungulates, transient movements of several ldlometres occur in. response to local rainfall or fresh green plant growth (Bothrna, 1972; Ghobrial, 1974), whereas longer-range movements follow traditional routes toward permanent water (Williamson & Williamson, 1985). Movements of 10-25 krn have been recorded in many species of herbivores toward ephemeral patches of green food (e.g. Newsome, 1965; McCullough, 1985; Croft, 1991), and in carnivores toward temporary aggregations of prey (Skinner & Smithers, 1990). Although increased access to resources is the most obvious benefit for migrants, Fryxell et al. (1988) have argued that migration in some ungulates also reduces the effects of sedentary predators. In contrast to the wealth of observations on birds and large mammals, there is scant evidence that long-range movements occur in desert-dwelling small mammals. In North America, for example, individuals of most species that have been studied appear to occupy discrete home ranges or territories (Jones, 1993; Randall, 1993). Maximum movements are associated with either juvenile dispersal (Jones, 1987; Lidicker & Patton, 1987) or dispersal of adults (Zeng & Brown, 1987; Brown & Zeng, 1989), but very seldom exceed 1 krn. Similar findings have been obtained for species of arid regions in southern Africa (Skinner & Smithers, 1990) and South America (Redford & Eisenberg, 1992). In Australia, however, anecdotal reports (e.g. Plomley, 1972) and incidental records (Read, 1984) of long-range movements suggest that small desert mammals may be more mobile than has been suspected previously. Such observations have implications for understanding the general ecology and minimum area requirements of small mammals. This understanding is particularly important in arid Australia, where rodents and small marsupials have suffered a high rate of extinction since European colonization (Burbidge & McKenzie, 1989; Morton, 1990; Dickman et al., 1993a), and where effective conservation of remaining species may depend on protection of large enough areas to maintain viable populations. In the present study, we (1) describe patterns of long-range movements of small mammals at two study areas in arid Australia, (2) relate movements to rainfall events, and (3) comment on the implications of our findings for land reservation and management.
Study areas
Data were collected from two study areas as part of broader studies on the ecology of terrestrial vertebrates. The first area is centred N 20 km north-east of Bulgalbin Hill in the western goldfields of Western Australia (30°16'S, 119°46'E). This area is an undulating yellow sand plain dominated by tall shrubs (Acacia coolgardiensis, Banksia elderana) and stands of mallee (Eucalyptus leptopoda), with a patchy ground cover of hummock grass (Plecrrachne sp.) and low perennial shrubs (Grevillea spp., Daviesia hakeoides, Calytrix cresswellii, Pachynema junceum and Melaleuca spp.) (Newbey & I-inatiuk, 1985). Rainfall averages 265 mm a year. The second study area is centred 15 km north of Ethabuka Station homestead on the eastern edge of the Simpson Desert, Queensland (23°46'S, 138°28'E). This area is characterized by long red sand dunes up to 8 m high that run south to north in line with the prevailing southerly winds (Twidale & Wopfiaer, 1990). Low trees (Acacia cambage0 occur in the dune swales. Hummock grass (Triodia basedowiz) dominates the ground level vegetation, with a scattering of low perennial shrubs (Crotalaria sp., Enchylaena tomentosa, Sclerolaena diacantha) occurring
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f r o m the dune sides to the crests. Rainfall is probably between 165 m m and 264 m m a year, as judged f r o m records of the nearest weather stations 245 k m to the south-east and 180 k m to the north-east, respectively (Bureau of Meteorology, 1988).
Methods Animals were live-captured using pitfall traps (16 c m wide and 5 0 - 6 0 cm deep) equipped with a 5 m drift fence of a l u m i n i u m flywire to enhance trap efficiency (Friend et al., 1989). In Western Australia, 12 × 0-6 ha grids of 30 pitfall traps were set 0-4-2-0 k m apart along an access track running in a roughly north-easterly direction, with the furthest grids being ~ 10 k m apart. In Queensland, 21 × 1.0 ha grids of 36 pitfall traps were set 0.5-2-0 k m apart running in a northerly direction, with the furthest being 14 k m apart. In b o t h study areas traps were checked once or twice a day for 2-7 consecutive days a b o u t once every 2 months. C a p t u r e d animals were weighed, sexed, checked for reproductive condition and given a unique m a r k by toe or ear clipping. M o v e m e n t s were recorded by measuring linear distances between recaptures. We define short-range m o v e m e n t s as distances m o v e d within grids ( < 100 m) and long-range m o v e m e n t s as distances m o v e d between them. T r a p p i n g was carried out at Bungalbin Hill between N o v e m b e r 1987 and M a y 1989, and in the Simpson Desert between M a r c h 1990 and July 1993. T o t a l trapping effort ( n u m b e r of traps set × n u m b e r of nights open) was 57,300 trap nights. T o investigate possible effects of rain, we c o m p a r e d distances m o v e d between grids by small m a m m a l s during dry periods with m o v e m e n t s that occurred during periods of rain or within a m o n t h of rain having fallen in the study regions. Detailed records of rainfall were available f r o m a rain gauge at the Bungalbin Hill study area, and f r o m a gauge at Ethabuka Station h o m e s t e a d 15 k m south of the study area in the Simpson Desert. Further qualitative records of rainfall were m a d e by noting the presence of standing water at the study areas and on tracks leading to and f r o m them.
Results
Capture statistics Eleven species of small m a m m a l s were captured at Bungalbin Hill and 13 in the Simpson Desert, six species were found at b o t h study areas (Table 1). Species differed dramatically in a b u n d a n c e within areas. T h e m o r e c o m m o n species in each area were represented by hundreds of individuals over the course of the study, whereas at the opposite extreme the dasyurid marsupial Sminthopsis macroura was represented by only two captures over three years in the Simpson Desert and the h o p p i n g - m o u s e Notomys alexis was recorded twice at Bungalbin Hill. Rodents p r e d o m i n a t e d in b o t h areas. Individuals were recaptured relatively infrequently (Table 1); the m e a n recapture rate across all species was 11-3%, ranging f r o m 6.8% in Pseudomys hermannsburgensis to 73-8% in Sminthopsis hirtipes. Just u n d e r half of all recaptures (44.8%, n = 223) occurred within trapping sessions, with very few (1.2%, n = 6) occurring a year or m o r e later. Population sizes of the m o r e c o m m o n species, represented simply by n u m b e r s of captures, fluctuated greatly between trapping sessions (Table 1). T h e s e large numerical fluctuations and the low recapture rates suggest that individuals are highly mobile and populations transient over short periods.
C. R. DICKMAN E T A L .
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SMALLMAMMALMOVEMENTS IN ARID AUSTRALIA
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Movements Most individuals were recaptured on the grid of their initial capture, but small numbers moved between grids for distances up to 14 km (Fig. 1). Movements within trapping sessions were predominantly short-range, accounting for 91.5% (n = 204) of all movements within sessions. Within-session short-range movements varied from 78.8% of recaptures in P. albocinereus to 97.7% in P. hermannsburgensis. T h e r e was no clear tendency for long-range movements to increase over time. Distance moved was weakly correlated with n u m b e r of months between captures in N. alexis (r = + 0.41, p = 0-05), but not in any other species (r values ranged from + 0.03 to + 0-47, p = NS). T h e total n u m b e r of long-range movements in all species (n = 99) represented 19.9% of the movements recorded (n = 498). T h e occurrence of longrange movements was similar in rodents (18.8%) and dasyurids (24.0%); long-range m o v e m e n t was most prevalent in P. albocinereus (44.0%) and least in R. villosissimus (2.99%). Rodents generally moved further than marsupials, with 10 of the 14 longest ( > 10 kin) movements being made by P. hermannsburgensis, three by N. alexis, and only one movement, of 12 km, by S. youngsoni (Fig. 1). Excluding recaptures within grids, mean distances moved ranged from 1.04 km in Sminthopsis hirtipes to 6.34 km in P. hermannsburgensis. T h e occurrence of long-range movements differed between species of similar mean body mass, such as N. alexis and P. albocinereus, or S. hirtipes and S. dolichura, thus providing no indication that distance moved is related to body size (cf. Fig. 1 and Table 1). Within each species, movements between grids were made by both sexes, by juveniles and by breeding and non-breeding adults. T o determine whether any class of animals within each species population was more or less likely to move, we compared the proportions of individuals in all sex/age categories moving between grids over the course of the study, with the proportions in the same categories in the populations. N o test results were significant (X2 < 3.84, 1 dr., p > 0.05 for all tests, using correction for
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Distance moved (kin)
Figure 1. Distances moved by six species of small mammals in two study areas in arid Australia, (a) Bungalbin Hill in Western Australia and (b) Ethabuka Station in Queensland. Movements are defined as recaptures within trapping grids (<0.1 kin) or between grids (a 0.1 km), and numbers of movements are shown as log (x + 1). Two movements by Rattus villosissirnus of 0"75 and 2.05 km are not shown. The absence of recaptures at distances of 0.10-0.49 km at Ethabuka Station reflects the lack of trapping grids in this distance class. (a) [] = Pseudomys albodnereus; • = Sminthopsis hirtipes; [] = Sminthopsis dolichura. (b) [] = Pseudomys hermannsburgensis; [] = Notomys alexis; [] = Sminthopsis youngsoni.
C. R. DICKMANETAL.
446
Table 2. Long-distance (between-grid) movements of smodl mammals at.two
study areas in arid Australia in relation w rainfall Distance moved, km +- S.D. (n) During dry periods
During or after rain
t
p
1-42+1.40(13) 0.76+-0.34(7) 2.90+2.72(4)
2.86+-2.84(9) 1.32+_0-67(7) 4-20(1)
1.66 2.00 --
NS NS --
5.63+5"57(11) 1-38+0.88(11) 1.40+_0.92(2) 0-96+_0.34(4)
6-82+4"86(16) 5.45+5-42(12) -7"25+_6"72(2)
0"36 2.45 -2.15
NS <0.05 -NS
Bungalbin Hill, W.A.
Pseudomys albocinereus Sminthopsis hirtipes Sminthopsis dolichura Simpson Desert, Queensland Pseudomys hermannsburgensis Nowmys alexis Ratrus villosissimus Sminthopsis youngsoni NS = not significantat a = 0.05.
continuity), suggesting that neither sex nor age nor reproductive status predispose individuals to move. Inspection of the raw capture data indicated that long-range movements occurred at all times of year, but appeared to be associated particularly with periods of rainfall. Movements ranged from being 21.1% greater during or after rainfall than during dry periods for Pseudomys hermannsburgensis, to 6.5-fold greater in Sminthopsis youngsoni, with an average increase across all species of almost 200% (Table 2). Increased movement was statistically significant only in Notomys alexis, but approached significance (0.1 > p > 0.05) in Sminthopsis hirtipes and S. youngsoni. Sixteen of 47 long-distance movements occurred during or after rain on the study areas, whereas 31 movements occurred within a m o n t h of rain that fell up to 15 krn away from the grids. O f these latter movements, 23 (74.2%) were in a northerly or southerly direction toward the area of rainfall. This orientation toward rain is significant (X2co~ = 6.32, p < 0-05), if it is assumed that there is an equal probability of movement toward or away from precipitation.
Discussion
Long-range movements T h e maximum distances moved by small mammals in this study generally exceed those reported elsewhere in Australia. In semi-arid grassland in New South Wales, for example, Read (1984) noted an exceptional movement by Sminthopsis crassicaudata of 5 km and a maximum movement by Planigale gilesi of 1"3 km. Ram~s villosissimus may be more mobile, with distances of - 3 km being covered per day during plagues (Finlayson, 1939), but movements by marked individuals have been little studied (Prevadec & Dickman, 1994). Movements of small mammals in temperate and tropical parts of Australia appear to be particularly limited, with distances of > 1 km being seldom recorded (e.g. Wood, 1970, 1971; Smith, 1984; Leung et al., 1993). In part, the appearance of limited movement in previous studies may be due to use of relatively small sampling areas that reduce the chance of long-range recaptures, and infrequent use of alternative methods such as radio-telemetry. However, observations of homing behaviour (Fox & Cooper, 1982) and studies using a similar dispersion of
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grids to that in the present work (Dickman, 1980, 1986) suggest that lifetime movements of small mammals in non-arid Australian environments seldom exceed 2-3 km. There is little evidence of greater mobility of small mammals either in temperate environments outside Australia (e.g. Kirkland, 1988; Dickman & Doncaster, 1989), or in other world deserts (e.g. Brown & Zeng, 1989; Ascaray & McLachlan, 1990). Although we recorded several individuals moving up to 14 km, the true magnitude of long-distance movements within species populations was probably much greater than the records suggest. In the first instance, the nearly linear disposition of the trapping grids ensured that only those animals moving in northerly or southerly directions would have been at risk of capture. If movements occur equally in all directions, our grids would have intercepted < 5% of all dispersers. Secondly, the rate of recapture for all species was relatively low, within and between field trips, whereas the rate of appearance of new individuals was high. Similarly high rates of population turnover have been reported for small mammals elsewhere in arid Australia (Dunlop & Sawle, 1982; Masters, 1993), and may characterize species with unstable, drifting 'home ranges' (Morton, 1978; Read, 1984). The factors that promote long-range movements of arid-zone small mammals cannot be specified precisely, but several observations suggest that rainfall may be important. Firstly, movements tended to increase after rain, and were directed toward areas where rain had fallen. Secondly, populations of rodents increased locally on both study areas after rain, suggesting that immigrants had moved from surrounding areas. At Bungalbin Hill, numbers of P. albocinereus were 82% higher in November and December 1988 (n = 40) less than six weeks after rain had fallen, than during the same period in 1987 (n = 22) when conditions were dry. T h e increase in 1988 was due entirely to immigration because the time from conception to weaning in P. albocinereus is too long (73-74 days; Watts, 1982) to have allowed population increase via reproduction. In the Simpson Desert, Predavec (1994) described dramatic increases in numbers of P. hermannsburgensis and N. alexis after rain; the relative contributions of immigration and in situ reproduction to the population increases are unclear, but some movement is probably involved. Finally, we recorded an extension of range of the hairy-footed dunnart Sminthopsis hirtipes into the eastern Simpson Desert in 1992; this appeared to be due to long-range movements of individuals following unusually heavy rainfall (Dickman et aL, 1993b). Rain may be used most obviously as a source of free water by small mammals, but it is probably still more important in increasing food resources. For rodents, rain may produce an immediate increase in food by enhancing the accessibility of bu0.'ed seeds. Johnson & Jorgensen (1981) showed that several species of rodents in North American deserts find more seeds buried in moist than in dry sand, apparently because moistened seeds provide relatively strong olfactory cues. Vander Wall (1993) demonstrated further that hydrated seeds are more vulnerable to foragers than dry seeds when buried in dry sand. Rain may also have longer-term effects by promoting plant growth. Th e rodents we studied are omnivorous and eat the green stem, leaf material and fungi, as well as seeds, that become more abundant after rain (Murray & Dickman, 1994), whereas dasyurids are broadly insectivorous and may utilize increased invertebrate populations (Fisher & Dickman, 1993). Movements from drought-affected areas with diminished resources to resource-rich sites may thus be advantageous, providing fitness benefits to individuals that move. In contrast, nonmovement may represent a particularly risky strategy for individuals living in an impoverished area. Spatial and temporal predictability of local rainfall is very low in arid Australia (Gentilli, 1972; Fleming, 1978); hence sedentary individuals should face considerable uncertainty that conditions will improve in a local area within their lifetime. In arid areas outside Australia, more reliable rainfall may allow greater or more
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continuous production of food resources for small mammals, and minimize any benefits of long-range movement. Further, caching of food, which has been described in a wide variety of desert-dwelling cricetid and heteromyid rodents (de Graaf, 1981; Downs & Perrin, 1989; Randall, 1993; Reichman & Price, 1993), probably provides a buffer against temporary food shortage. There is little evidence that similar behaviour is exhibited by either rodents or dasyurids in arid Australia (Watts & Aslin, 1981; cf. Baker et M., 1993). Physiological adaptations that temporarily reduce demand for food, such as facultative heterothermy, are also prevalent in heteromyids (French, 1993). Only P. herrnannsburgensis in arid Australia is suspected to be able to enter torpor (Predavec, 1994). The importance of drought-refuge sites has been documented for many species of terrestrial vertebrates in arid Australia (Finlayson, 1943; Watts & Aslin, 1974), and the concept of shifting refugia has been recognized explicitly by Newsome & Corbett (1975). Morton (1990) has proposed further that the recent degradation of refuge sites by introduced herbivores in arid Australia has contributed to losses of medium-sized mammals, whereas smaller species (< 35 g) have persisted because their resource requirements can be met in smaller, disturbed patches. Our results suggest that persistence of small mammals may be facilitated also by their extraordinary mobility, which should allow colonization of transient patches regenerating after rain even if these are scattered widely over the desert landscape. Long-distance movement should be especially important if rain falls on drought-struck areas containing in situ populations too low to respond quickly to resource pulses. These conclusions accord with theoretical predictions that the persistence of populations at the regional level will be increased by asynchronous fluctuations among constituent local populations; if any one local population disappears, recolonization by migrants will prevent extinction of the whole (Allen et al., 1993).
Implications for conservation and land management
For long-term conservation of add-zone small mammals, and other biota, it is clear that land must be managed to protect not only permanent oases (Morton, 1990), b u t also the ephemeral refugia of increased productivity that appear after local rains and disappear during droughts. Because they are fixed, permanent refugia such as oases and riverine strips can be identified readily and protected by means such as land reservation. Systematic methods of reserve selection are available for such refugia (e.g. Pressey & Nicholls, 1989a, b, 1991), and an hierarchical system of land uses has been proposed that would focus management on the most critical sites (Morton et al.,
1995). In contrast, ephemeral refugia are not spatially predictable and could be expected to occur frequently outside of reserved land. These could be colonized by small mammals only if the non-reserved land surrounding them was traversable. Land use in arid Australia is dominated by the pastoral industry, but substantial areas are used also for resource exploration, mining and tourism; much of this land is degraded and of poor quality for small mammals (Stanley, 1983; Dickman, 1993). An approach to protecting ephemeral land patches and the small mammals and other biota that use them is to aim for improved land management outside national parks and other reserves. This approach recognizes the practical reality that a large and fully representative reserve system may be difficult to achieve in arid Australia, and also that reserves will be more effective if they are not embedded in a hostile landscape (Schonewald-Cox & Bayless, 1986). Conservation goals will clearly be difficult to achieve without the full cooperation of all land users and local communities. In South Australia, a cooperative approach is being pioneered toward ecologically sustainable land care in large, multiple-use regional reserves, with conservation remaining as the
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major objective (Cohen, 1990, 1992). M o r e generally, M o r t o n et al. (1995) have emphasized the importance of seeking c o m m o n , regional stewardship in arid Australia, and offer a practical structure for identifying and managing different categories of sustainable land uses. We agree with this holistic view, and believe that appropriate regional scale m a n a g e m e n t will be crucial for conservation of mobile organisms, such as small mammals, which have m u c h larger area requirements than have been appreciated hitherto. We thank the many volunteers who assisted at different times with fieldwork, especially H. Braak, H. Brurmer, J. Richards and P.C. Withers. We also thank D. and P. Smith for their hospitality and access to Ethabuka Station, and R.P. Kavanagh, and M.B. Thompson for commenting critically on the manuscript. The research was supported by grants from the Australian Research Council (to CRD) and the Australian Geographical Society, Australian Museum Postgraduate Grant Scheme and Ethel Mary Read Fund of The Royal Zoological Society of New South Wales (to M.P).
References Allen, J.C., Schaffer, W.M. & Rosko, D. (1993). Chaos reduces species extinction by amplifying local population noise. Nature, 364: 229-232. Ascaray, C.M. & McLachlan, A. (1990). Home range of Gerbilluruspaeba in a southern African coastal dunefield. Zeitschriftfiir Saugetierkunde, 55: 399-406. Bailey, P.T. (1971). The red kangaroo, Megaleia tufa (Desmarest), in north-western New South Wales. CSIRO Wildlife Research, 16:11-28. Baker, L., Woenne-Green, S. & the Mutitjulu Community (1993). An_angu knowledge of vertebrates and the environment. In: Reid, J.R.W., Kerle, J.A. & Morton, S.R. (Eds), Kowari 4: Uluru Fauna, pp.79-132. Canberra: Australian National Parks and Wildlife Service. 152 pp. Bothma, J. du P. (1972). Short-term response in ungulate numbers to rainfall in the Nossob River of the Kalahari Gemsbok National Park. Koedoe, 15: 127-133. Brown, J.H. & Zeng, Z. (1989). Comparative population ecology of eleven species of rodents in the Chihuahuan Desert. Ecology, 70: 1507-1525. Burbidge, A.A. & McKenzie, N.L. (1989). Patterns in the modem decline of Western Australia's vertebrate fauna: causes and conservation implications. BiologicalConservation, 50: 143-198. Bureau of Meteorology. (1988). Climatic Averages Australia. Canberra: Australian Government Publishing Service. 532 pp. Cohen, B. (1990). Reconstruction of South Australia's arid lands: the conservation option. Proceedings of the Ecological Society of Australia, 16: 459-465. Cohen, B. (1992). Multiple use and nature conservation in South Australia's arid zone. Rangeland ffournal, 14:205-214. Croft, D.B. (1991). Home range of the red kangaroo Macropus rufus, ffournal of Arid Environments, 20: 83-98. Davies, S.J.J.F. (1984). Nomadism as a response to desert conditions in Australia. ffournal of Arid Environments, 7: 183-195. Davies, S.J.J.F., Beck, M.W.R. & Kruiskamp, J.P. (1971). The results of banding 154 emus in Western Australia. CSIRO Wildlife Research, 16: 77-79. de Graaff, G. (1981). The Rodents of Southern Africa. Durban: Butterworths. 267 pp. Denny, M.J.S. (1975). The occurrence of the eastern grey kangaroo west of the Darling River. Search, 6; 89-90. Denny, M.J.S. (1982). Adaptations of the red kangaroo and euro (Macropodidae) to aridity. In: Barker, W.R. & Greenslade, P.J.M. ('Eds), Evolution of the Flora and Fauna of Arid Australia, pp. 179-183. Frewville: Peacock Publications. 392 pp. Dickrnan, C.R. (1980). Ecological studies of Antechinus stuartii and Antechinus flavipes (Marsupialia: Dasyuridae) in open-forest and woodland habitats. Australian Zoologist, 20: 433-446. Dickrnan, C.R. (1986). Niche compression: two tests of an hypothesis using narrowly sympatric predator species. Australian ffournal of Ecology, 11: 121-134.
450
C. P,. DICKMANETAL.
Dickman, C.R. (1993). The biology and management of native rodents of the arid zone in N.S.W. New South Wales National Parks and Wildlife Service Species Management Report, 12: 1-149. Dickman, C.R. & Doncaster, C.P. (1989). The ecology of small mammals in urban habitats. II. Demography and dispersal, ffournal of Animal Ecology, 58:119-127. Dickrnan, C.R., Pressey, R.L., Lira, L. & Pamaby~ H.E. (1993a). Mammals of particular conservation concern in the Western Division of New South Wales. Biological Conservation, 65: 219-248. Dickman, C.R., Downey, F.J. & Predavec, M. (1993b). The hairy-footed dunnart Sminthopsis hirtipes (Marsupialia: Dasyuridae) in Queensland. Australian Mammalogy, 16: 69-72. Downs, C.T. & Perrin, M.R. (1989). An investigation of the macro- and micro- environments of four Gerbillurus species. Cimbebasia, 11: 41-54. Dunlop, J.N. & Sawle, M. (1982). The habitat and life history of the Pilbara ningaui Ningaui timealeyi. Records of the Western Australian Museum, 10: 47-52. Firdayson, H.H. (1939). On mammals from the Lake Eyre basin. Part V. General remarks on the increase of murids and their population movements in the Lake Eyre basin during the years 1930-1936. Transactions of the Royal Society of South Australia, 63: 348-353. Finlayson, H.H. (1943). The Red Centre. Sydney: Angus & Robertson. 153 pp. Fisher, D.O. & Dicknaan, C.R. (1993). Diets of insectivorous marsupials in arid Australia: selection for prey type, size, or hardness? Journal of Arid Environments, 25: 397-410. Fleming, P.M. (1978). Types of rainfall and local rainfall variability. In: Howes, K.M.W. (Ed.), Studies of the Australian Arid Zone. Part 111. Water in rangelands, pp. 18-28. Melbourne: CSIRO. 225 pp. Fox, B.J. & Cooper, W.T. (1982). Homing in Antechinus stuartii (Marsupialia: Dasyuridae). Australian Mammalogy, 5:71-73. French, A.R. (1993). Physiological ecology of the Heteromyidae: economics of energy and water utilization. In: Genoways, H.H. & Brown, J.H. (Eds), Biology of the Heteromyidae, pp. 509-538. The American Society of Marnmalogists. 719 pp. Friend, G.R., Smith, G.T., Mitchell, D.S. & Dickman, C.R. (1989). Influence of pitfall and drift fence design on capture rates of small vertebrates in semi-arid habitats of Western Australia. Australian Wildlife Research, 16: 1-10. Frith, H.J. (1959). The ecology of wild ducks in inland New South Wales II. Movements. CSIRO Wildlife Research, 4: 108-130. Frith, H.J. (1962). Movements of the grey teal, Anas gibberffrons Muller (Anatidae). CSIRO Wildlife Research, 7: 50-70. Fryxell, J.M., Greever, J. & Sinclair, A.R.E. (1988). Why are migratory ungulates so abundant? American Naturalist, 131: 781-798. Genfilli, J. (1972). Australian Climate Patterns. Melbourne: Nelson. 285 pp. Ghobrial, L.I. (1974). Water relation and requirement of the dorcas gazelle in the Sudan. Mammalia, 38: 88-107. Johnson, T.K. & Jorgensen, C.D. (1981). Ability of desert rodents to find buried seeds. Journal of Range Management, 34:312-314. Jones, W.T. (1987). Dispersal patterns in kangaroo rats Dipodomys spectabilis. In: Chepko-Sade, B.D. & Halpin, Z.T. (Eds), Mammalian Dispersal Patterns, pp. 119-127. Chicago: University of Chicago Press. 342 pp. Jones, W.T. (1993). The social systems of heteromyid rodents. In: Genoways, H.H. & Browne J.H. (Eds), Biology of the Heteromyidae, pp.575-595. The American Society of Mammalogists. 719 pp. Kirldand, G.L., Jr. (1988). Meadow voles Microtuspennsylvanicus on forest clearcuts: the role of long-distance dispersal. Journal of the Pennsylvania Academy of Science, 62: 83-85. Leung, L.K.-P., Dickrnan, C.R. & Moore, L.A. (1993). Genetic variation in fragmented populations of an Australian rain.forest rodent, Melomys cervinipes. Pacific Conservation Biology, 1: 58-65. Lidicker, W.Z., Jr. & Patton, J.L. (1987). Patterns of dispersal and genetic structure in populations of small rodents. In: Chepko-Sade, B.D. & Halpin, Z.T. (Eds), Mammalian Dispersal Patterns, pp. 144-161. Chicago: University of Chicago Press. 342 pp. Masters, P. (1993). The effects of fire-driven succession and rainfall on small mammals in spinifex grassland at Uluru National Parks Northern Territory. Wildlife Research, 20: 803-813.
SMALLMAMMALMOVEMENTSIN ARIDAUSTRAJ_JA
451
McCullough, D.R. (1985). Long range movements of large terrestrial mammals. Contributions in Marine Science, 27 (Supplement): 44~ ~65. Morton, S.R. (1978). An ecological study ofSminthopsis crassicaudata (Marsupialia: Dasyuridae) II. Behaviour and social organization. Australian Wildlife Research, 5: 163-182. Morton, S.R. (1990). The impact of European settlement on the vertebrate animals of arid Australia: a conceptual model. Proceedings of the Ecological Society of Australia, 16: 201-213. Morton, S.R., Stafford Smith, D.M., Friedel, M.H., Griffin, G.F. & Pickup, G. (1995). The stewardship of arid Australia: ecology and landscape management. Journal of Environmental Management (in press). Murray, B.R. & Dickman, C.R. (1994). Granivory and microhabitat use in Australian desert rodents: are seeds important? Oecologia, 99: 216-225. Newbey, K.R. & Hnatiuk, R.J. (1985). Vegetation and flora. Records of the Western Australian Museum, 23 (Suppl.): 11-38. Newsome, A.E. (1965). The distribution of red kangaroos about sources of persistent food and water in central Australia. Australian Journal of Zoology, 13: 289-299. Newsome, A.E. & Corbett, L.K. (1975). Outbreaks of rodents in semi-arid and arid Australia: causes, preventions, and evolutionary considerations. In: Prakash, I. & Ghosh, P.K. (Eds), Rodents in Desert Environments, pp. 117-153. The Hague: Junk. 624 pp. Nix, H.A. (1976). Environmental control of breeding, post-breeding dispersal and migration of birds in the Australian region. In: Frith, H.J. & Calaby, J.H. (Eds), Proceedings of the 16th International Ornithological Congress, pp. 272-305. Canberra: Australian Academy of Science. 765 pp. Plomley, N.J.B. (1972). Some notes on plagues of small mammals in Australia. Journal of Natural History, 6: 363-384. Predavec, M. (1994). Food limitation and demography in Australian desert rodents. Ph.D. thesis, University of Sydney, Sydney. Predavec, M. & Dickman, C.R. (1994). Population dynamics and habitat use of the long-haired rat (Rattus villosissimus) in south-western Queensland. Wildlife Research, 21:1-10. Pressey, R.L. & Nicholls, A.O. (1989a). Efficiency in conservation evaluation: scoring versus iterative approaches. Biological Conservation, 50 199-218. Pressey, R.L. & Nicholls, A.O. (1989b). Application of a numerical algorithm to the selection of reserves in semi-arid New South Wales. Biological Conservation, 50: 263-278. Pressey, R.L. & Nicholls, A.O. (1991). Reserve selection in the Western Division of New South Wales: development of a new procedure based on land system mapping. In: Margules, C.R. & Austin, M.P. (Eds), Nature Conservation: Cost effective biologicalsurveys and data analysis, pp. 98-105. Melbourne: CSIRO. 207 pp. Randall, J.A. (1993). Behavioural adaptations of desert rodents (Heteromyidae). Animal Behaviour, 45: 263-287. Read, D.G. (1984). Movements and home ranges of three sympatric dasyurids, Sminthopsis crassicaudata, Planigale gilesi and P. tenuirostris (Marsupialia), in semiarid western New South Wales. Australian Wildlife Research, 11: 223-234. Redford~ K.H. & Eisenberg, ~[.F. (1992). Mammals of the Neotropics: The southern cone. Chicago: University of Chicago Press. 430 pp. Reichman, O.J. & Price, M.V. (1993). Ecological aspects ofheteromyid foraging. In: Genoways, H.H. & Brown, J.H. (Eds), Biology of the Heteromyidae, pp. 539-57.4. The American Society of Mammalogists. 719 pp. Schodde, R. (1982). Origin, adaptation and evolution of birds in arid Australia. In: Barker, W.R. & Greenslade, P.J.M. (Eds), Evolution of the Flora and Fauna of Arid Australia, pp. 191-224. Frewville: Peacock Publications. 392 pp. Schonewald-Cox, C.M. & Bayless, J.W. (1986). The boundary model: a geographical analysis of design and conservation of nature reserves. Biological Conservation, 38: 305-322. Skinner, J.D. & Smithers, R.H.N. (1990). The Mammals of the Southern Aft'can Subregion. Pretoria: University of Pretoria. 771 pp. Smith, G.C. (1984). The biology of the yellow-footed antechinus, Antechinus flavipes (Marsupialia: Dasyuridae), in a swamp forest on Kinaba Island, Cooloola, Queensland. Australian Wildlife Research, 11: 465480. Stanley, R.J. (1983). Soils and vegetation: an assessment of current status. In: Messer, J. & Mosley, G. (Eds), What Future for Australia's Arid Lands? pp. 8-18. Hawthorn: Australian Conservation Foundation. 206 pp.
452
C.R. DICKMANETAL
Talbot, L.M. & Talbot, M.H. (1963). The wildebeest in western Masailand, East Africa. Wildlife Monographs, 12: 1-88. Twidale, C.R. & Wopfiaer, H. (1990). Dune fields. In: Tyler, M.J., Twidale, C.R., Davies, M. & Wells, C.B. (Eds), Natural History of the North East Deserts, pp. 45-60. Adelaide: Royal Society of South Australia. 226 pp. Vander Wall, S.B. (1993). Seed water content and the vulnerability of buried seeds to foraging rodents. American Midland Naturalist, 129:272-281. Watts, C.H.S. (1982). Australian hyclromyine rodents: maintenance of captive colonies. In: Evans, D.D. (Ed.), The Management of Australian Mammals in Captivity, pp. 180-184. Melbourne: Zoological Board of Victoria. 188 pp. Watts, C.H.S. & Aslin, H.J. (1974). Notes on the small mammals of north-eastern South Australia and south-western Queensland. Transactions of the Royal Society of South Australia, 98: 61-69. Watts, C.H.S. & Aslin, H.J. (1981). The Rodents of Australia. Sydney: Angus & Robertson. 321 pp. Williamson, D. & Williamson, J. (1985). Botswana's fences and the depletion of Kalahafi wildlife. Parks, 10: 5-7. Wood, D.H. (1970). An ecological study of Antechinus stuartii (Marsupialia) in a south-east Queensland rain forest. Australian Journal of Zoology, 18: 185-207. Wood, D.H. (1971). The ecology of Rartus fuscipes and Melomys cervinipes (Rodentia: Muridae) in a south-east Queensland rain forest. Australian Journal of Zoology, 19:371-392. Zeng, Z. & Brown, J.H. (1987). Population ecology of a desert rodent: Dipodomys merriami in the Chihuahuan Desert. Ecology, 68: 1328-1340.