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Dynamics of a thermo-Mediterranean coastal environment – the Coto Doñana National Park
Quaternary Science Reviews 27 (2008) 2145–2152
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Dynamics of a thermo-Mediterranean coastal environment – the Coto ˜ ana National Park Don Geraldine Finlayson a, *, Clive Finlayson a, b, J.M. Recio Espejo c a
The Gibraltar Museum, 18–20 Bomb House Lane, Gibraltar Department of Social Sciences, University of Toronto, Scarborough Campus, Toronto, Canada c ´ rdoba, Co ´rdoba, Spain Departamento de Ecologia, Universidad de Co b
a r t i c l e i n f o
a b s t r a c t
Article history: Received 27 March 2008 Received in revised form 23 July 2008 Accepted 1 August 2008
Using data collected from existing habitats found in the southwestern Iberian Peninsula, and including ˜ ana, Spain, this study considers the data collected in the Biological Reserve of the Parque Nacional de Don seasonal and inter-annual variability of a thermo-Mediterranean, subhumid, environment and the significance of the presence of surface water in the system. This extant environment is then used together with the fossil record from Gorham’s Cave in Gibraltar, where Neanderthals lived, as a proxy for the ecology of the emerged landscape outside the cave. Ó 2008 Elsevier Ltd. All rights reserved.
1. Introduction The southern Iberian coastal site of Gorham’s Cave, Gibraltar, has been recently shown to have been a refuge for a number of species and the last known site of Neanderthal survival (Finlayson, 2006; Finlayson et al., 2008). The habitat outside Gorham’s Cave during the period of the last Neanderthals (32–24 ka) has been reconstructed using data from charcoal remains, pollen and bird remains within the stratigraphy of the site (Finlayson, 2006; Finlayson et al., 2007). The dominant habitat is an open woodland ‘savannah’ with patches of denser woodland and thickets. The thermophilous stone pine, Pinus pinea, is the main component of an essentially thermo-Mediterranean, subhumid, environment. This paper analyses an analogous coastal landscape that can be found today on the southwestern coast of Iberia (Fig. 1). The Bio˜ ana, Huelva (Spain), logical Reserve of the Parque Nacional de Don was the subject of a three-year study, from September 1993 to September 1996, which investigated the seasonal dynamics of birds and vegetation. The data presented in this paper provide information on seasonality as well as between-year variation, as a proxy for the environment in which the last Neanderthals lived. 2. Methods The study was carried out during monthly visits to the Reserve. On each of these visits, surveys were spread out over a two-day period. Twenty-one study plots were selected at intervals of 0.5 km,
* Corresponding author. E-mail address: [email protected] (G. Finlayson). 0277-3791/$ – see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.quascirev.2008.08.031
and a one-hectare sample within each study plot was divided into six separate zones. These plots were part of a wider Iberian survey that sampled a total of 980 plots (Finlayson, 2006). In each plot, birds were recorded between sunrise and the end of the morning activity; and the second day was dedicated to completing the bird census, when necessary, and to the vegetation survey. A record was also kept of the mammals observed during the standard sampling period (Finlayson, 2006; Finlayson et al., 2007). The largely undisturbed Biological Reserve was ideal for monitoring the distribution of birds and mammals (Finlayson et al., 2007). 3. Regional setting – the study site ˜ ana National Park are located within the The marshes of the Don delta of the Guadalquivir River between 6150 –6 300 W and 36 500 – 37100 N. Intense human activities have caused extensive modifications so that since the end of the 19th century, when the marsh area encompassed 140,000 ha, it had been reduced in 1996 to only 30,000 ha of virtually untouched habitats. These habitats form the strictly protected Biological Reserve that was the area chosen for the study (Finlayson, 2006). The marshes are the result of the progressive evolution of the ancient estuary of the Guadalquivir River, being cut off from the sea ˜ ana and Algaida) which have by a sand barrier of mobile dunes (Don been built up throughout the Holocene. The area can be divided into three distinct zones, or geological units: the ancient depression, of tectonic origin, now silted up with deltaic deposits from the river, the large coastal plain locally covered with aeolian sands (las arenas) and the sand barrier (Stevenson, 1985; Rodrı´guez Ramı´rez et al., 2005). The marsh (‘La Marisma’) covers 20,000 ha inside the Park. The dune system is composed of stabilised dunes, which form a series of
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Pistacia lentiscus, Monte negro woodland including Olea europaea and Quercus suber and usually associated with a parkland environment, Monte negro hygrophytic woodland, the wettest of the monte negro woodlands with a higher incidence of Q. suber, Myrtus communis, Pyrus bourgeana also present, and a dense and often impenetrable understorey containing Arbutus unedo, Smilax aspera, Rubia peregrina and Lonicera periclymenum, and Tamarix type, dominated by Tamarix africana, Tamarix canariensis and Populus alba. Fraxinus angustifolia and T. africana are also present in a wetter variant of the Quercus communities.
Fig. 1. Map of the study area with the Don˜ana National Park highlighted by a square.
arched ridges (old dunes) separated by flat depressions (old slacks). The geomorphology is conditioned by the evolution of the fluvial system, which has carved out a series of elevated channels (paciles). These in turn delimit enclosed hollows (‘lucios’), which, given the shallow water tables, frequently flood, filled with temporary lakes and ponds (‘lagunas’). There are mobile dunes, which advance at the rate of 5–6 m yr1 (Garcı´a Novo et al., 1975). These separate the marsh from the sea, and are in turn prevented from proceeding inland by the ancient meanders of the river. Climate is extremely seasonal and rainfall can vary significantly, averaging 550 mm yr1, and ranging between lows of 300 mm in 1980 and 1994 and highs of over 900 mm in 1987 and 1995 (Fig. 3). The bioclimatic attribution of all the study plots is thermoMediterranean, subhumid (Rivas-Martı´nez, 1987; Finlayson, 2006). Bioclimatically, the study area is comparable with the coastal plains that existed outside Gorham’s Cave for much of the last glacial cycle (Finlayson, 2006; Finlayson et al., 2007). 3.1. Vegetation The study site encompasses three types of vegetation that correspond to the following three main geomorphological units (Stevenson, 1985). 3.1.1. Marsh vegetation Open with very low grasses and forbs. 3.1.2. Stabilised dune vegetation Stevenson (1985) recognised three main succession groups, dependent on the depth of the water table: a) Grasslands, normally associated with areas where there is intensive grazing (e.g. by wild boar, Sus scrofa, fallow deer, Dama dama, or red deer, Cervus elaphus). b) Shrublands. These are characterised by three types of vegetation – the monte blanco which is the driest of the three with Lavandula stoechas, Helichrysum angustifolium, Halimium commutatum and Halimium halimifolium, the monte negro, characterised by the presence of Stauracanthus genistoides, H. halimifolium and Calluna vulgaris, and the monte negro hygrophytic shrubland, which is the wettest of the three and is dominated by Erica scoparia, but which also has the more drought sensitive Erica ciliaris, Ulex minor, Saccharum ravennae and Imperata cylindrica. c) Woods. These can also be subdivided into four different types according to the depth of the water table – Monte blanco woodland, which is the driest of the four, characterised by the presence of Juniperus phoenicea or Juniperus oxycedrus and
3.1.3. Mobile dune vegetation Vegetation here is dependent on the speed of movement of the dunes and the depth of the water table, and there are large areas of bare sands. The main shrub species is Corema album and the main tree species P. pinea, which is the only tree species that matures fast enough to keep pace with the movement of the dunes. The dune slacks are vegetated with Halimium spp. and P. pinea. ˜ana as a proxy for the Gorham’s Cave Neanderthal 3.2. Don environment The main plant taxa identified in the charcoal and pollen record in Gorham’s Cave are P. pinea, Juniperus spp., Quercus spp. (evergreen), Cistus–Halimium spp. and Erica spp. This particular combination is rare in any of the 980 1-ha study plots that have been investigated across the southwestern Iberian Peninsula (Finlayson, 2006), and in the present study (Table 1). ˜ ana Landscape Square are bioAll 21 study plots in the Don climatically thermo-Mediterranean, subhumid, whereas only 176 study plots (17.59%) out of the total analysed in Finlayson, 2006 fall into this bioclimatic zone of which 34.09% were those within ˜ ana (Finlayson et al., 2007). Don P. pinea is very locally distributed across much of southwestern Iberia, with only 87 (8.88%) out of the 980 study sites registering this species (Finlayson, 2006). Furthermore, the distribution of P. pinea is largely restricted to coastal areas. In the ˜ ana National Park, this 60 study plots that fell within the Don species is present in 20% of all plots. In the Biological Reserve it occupied 58% of the selected 21 plots. Likewise, compared to their representation in the 980 southwestern Iberian plots, Juniperus, Halimium and Erica are present in above average numbers ˜ ana (Table 1). in Don Given the uniqueness of these conditions within southwestern Iberia, and as a result of the high level of protection afforded to ˜ ana, we consider that the area of the Don ˜ ana National Park, Don and more specifically the Biological Reserve, is one of the few remaining zones within Iberia that can be used as a proxy for the habitats and landscapes that were located in the zone of the emerged shelf that existed outside Gorham’s Cave for much of the late Pleistocene.
Table 1 The frequency of the main plants identified in the Gorham’s Cave stratigraphy across ˜ ana. southwest Iberia and in Don
Pinus pinea Juniperus spp. Halimium spp. Quercus suber Cistus spp. Erica spp.
Presence in southwest Iberia (out of 980 study plots)
Frequency
Presence in ˜ ana (out of Don 60 study plots)
Frequency
87 85 56 216 234 67
8.88% 8.67% 5.71% 22.04% 23.88% 6.84%
12 6 18 3 9 15
20% 10% 30% 5% 15% 25%
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4. Results and discussion 4.1. Habitat structure Vegetation structure variables for grass, shrubs and trees are mapped as a 3D sequential graph to illustrate the spatial distribution of habitat variability (Fig. 2), along a transect which includes the ‘La Vera’ zone at the edge of the marsh (or ‘La Marisma’), the sands (‘las arenas’) and the area of the old dunes with temporary ponds and lakes (‘lagunas’). Study plots 1–7 on La Vera have virtually no trees and very few shrubs, but a presence of low and medium grasses. Towards the area of the old dunes – study plots 8–11 – the habitat changes with a greater abundance of medium and low shrubs, scattered trees, and very few grasses. Another change is apparent in study plot 12 with the presence of more trees and high shrubs, and an increase in grasses, including high grasses, which can be attributed to the higher water table in the area of the ponds and lakes. 4.2. Seasonality and between-year variability The study period covered an interval of intense drought following a period of heavy rainfall in 1989/1990 and gave way to a year with relatively high rainfall. Intense seasonal fluctuations as well as inter-annual variability in rainfall were therefore recorded during the study period (Fig. 3). The rainfall data available were then used to allocate an ombrotype for each year to show the variability from one year to the next. A Water Index (WI) – an estimate of standing water observed in each plot – was recorded, using a score based on the surface area covered by standing water, varying from 0 (no water) to 4 (>75% of surface with water). The scores for the six points in each plot were summed to give the PWI for the plot. Scores for all plots show a close relationship (R2 ¼ 0.718, p < 0.0001) with total rainfall recorded at the Palacio weather station (Fig. 4), demonstrating the validity of the water index as an easily obtained measure of water availability that can be plotted to show fine-scale variations in time and space (Fig. 5).
Fig. 2. Habitat structure of Don˜ana Biological Reserve transect. In this sequential plot, the values for each study plot are shown on the x-axis, and the vegetation sub-category along the y-axis. Shades refer to density of vegetation structural variables from grey (absent) to black (highest density). Categories were assigned as follows: grasses above 2 m GRAHI, those between 0.25 m and 2 m high GRAME, and those below 0.25 m in height GRALO. Shrubs above 2 m in height SHRHI, those between 0.25 m and 2 m tall SHRME and those up to 0.25 m SHRLO. Trees above 6 m TREHI, those between 2 m and 6 m TREME, and those below 2 m in height TRELO.
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A measure of variability in time and space was provided by the zone around plots 16 and 17 that often had some surface water present, but only on a seasonal basis, and the area became dry during the summer drought each year. The increase in rainfall commencing in January 1996 caused a marked increase in the amount of surface water present along the transect, and water persisted in the area of the lakes even throughout the summer drought of that year. The area of La Marisma/La Vera and a zone of temporary pools (plots 10–13), that had previously been dry throughout, also flooded. Spatio-temporal variation in vegetation features has been plotted in a similar manner (Fig. 6). Some features, such as trees, clearly changed little in the timescales involved. Changes in grasses were, however, notable, and this would be expected to have a significant impact on mammalian herbivores and grassland birds. Areas with grasses increased substantially in the wet period in 1996 but other areas showed a decrease in grass cover because standing water took over the zones where the grasses would normally be present. In general, there were some areas (e.g. plots 2–3, 5–6, 11– 12, 16–18) that favoured the development of grass cover, while other areas, covered by dense thickets (e.g. 8–10), only had grass cover after the heaviest rains. An estimate of bird species richness was obtained directly from the number of bird species present in each study plot. This was compared over time in the same type of 3D sequential graph (Fig. 7). Species richness was consistently highest in study plots 1– 7, which correspond to La Vera but even here the seasonality of the distribution was observed in a marked decrease of species richness during the summer drought. This richness in areas of ecological transition (ecotones) is well known (e.g. Kerr and Packer, 1997) and is clearly corroborated by this example. Seasonality was even more pronounced in study plots 10–13 and 15–19, which correspond to shrubland and lake areas, respectively. 4.3. Animal movements across the landscape over time The patchy distribution of water and plants over space and time is evident from Section 4.2. It gives an indication of the spatio-temporal patchiness of the kind of landscape that would have been used by prehistoric hunter-gatherers outside Gorham’s Cave during the last glacial cycle. We can take the comparison a stage further by looking at the distribution of birds and mammals in the same landscape. This permits inferences about ecosystem dynamics pertinent to the emerged coastal shelf of southern Iberia during the last glacial cycle. Ten species, or groups of species, of birds, and five species of large mammals were selected for analysis. The large mammals are ˜ ana. The birds chosen are taxa the principal species present in Don that are large and typical of the environment sampled. They are species that, in a prehistoric landscape (such as Gorham’s Cave), would have been significant to humans either as prey or as scavengers indicating the location of food sources. Although the analysis could have been conducted for other species, e.g. small insectivorous birds, these were not considered important in the context of the present study, and only selected species discussed below are illustrated graphically. a) Greylag goose, Anser anser (Fig. 8a). These birds are regular winter visitors and rely on grazing along the edges of the wetland. The seasonal concentration of these birds along La Vera is evident. The numbers were, paradoxically, lowest in the wettest winter. This reflected extensive flooding of grazing areas, forcing the birds to move to other zones of the Park or beyond. During the drought winters many carcasses of geese were observed in the dry Marismas. b) Ducks, Anas spp. Anas spp. were associated with the lakes and ponds, although they were also detected in La Vera. The
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450.00 Series1 400.00
Monthly Rainfall (mm)
350.00 300.00 250.00 200.00 150.00 100.00 50.00
M
79 S7 9 M 80 S8 0 M 81 S8 1 M 82 S8 2 M 83 S8 3 M 84 S8 4 M 85 S8 5 M 86 S8 6 M 87 S8 7 M 88 S8 8 M 89 S8 9 M 90 S9 0 M 91 S9 1 M 92 S9 2 M 93 S9 3 M 94 S9 4 M 95 S9 5
0.00
Date Fig. 3. Monthly rainfall recorded at the Palacio Don˜ana from October 1978 to January 1996.
presence of Anas spp. was highly seasonal, although as in the case of Anser, these too were negatively affected by the rainfall. The reason is that many of these ducks are surface feeders in shallow water and excessive water makes lakes and pools unsuitable. For these birds, and for the geese, intermediate rainfall years (neither too dry nor too wet) appeared optimal. c) The Red-legged partridge, Alectoris rufa (Fig. 8b) This is a seedeater and was present throughout the year and throughout the study area. Although it was most common in La Vera, it was also observed regularly near the lakes and ponds. Its presence did not appear to be affected by rainfall. Fewer birds were observed in spring when breeding pairs were notoriously shy and skulking. This is an abundant species in the Gorham’s Cave deposits. d) Quail, Coturnix coturnix (Fig. 8c). Quails are trans-Saharan migrants. They arrive to breed in the Park from tropical Africa in the spring. This species was only observed during the years of high rainfall, and they were present in both the area of La
Vera as well as the area of the lakes and ponds. The presence of this species is therefore highly erratic depending entirely on years with exceptionally high rainfall, not breeding in years of drought. Its presence is related to the increase in grass cover following heavy rainfall. This is an abundant species in Gorham’s Cave. e) Red kite, Milvus milvus. This is a resident raptor and regular scavenger. It was sporadically observed, although mainly over La Vera and the stabilised dunes, but it was also recorded over the lakes. This is a regular species in the Gorham’s Cave sequence. f) Black kite, Milvus migrans. This species is a regular scavenger and predator of small mammals, birds and frogs. This summer visitor was observed more frequently than Red kite, M. milvus. It was more widely distributed but seasonally absent in winter
80 Series1 70
Water Index (%)
60 50 40 30 20 10 0 0.00
50.00
100.00
150.00
200.00
250.00
300.00
350.00
Rainfall (mm) Fig. 4. Regression of the percentage Water Index (WI%) against the monthly rainfall in the Don˜ana Biological Reserve.
Fig. 5. 3D sequential graph showing the distribution of standing water over time. Shades refer to amount of standing water present from light grey (absent) to dark grey (highest cover). (PWI represents the proportion of the highest WI recorded over the three years of the study).
G. Finlayson et al. / Quaternary Science Reviews 27 (2008) 2145–2152
06/96
17-18 16-17 15-16 14-15
j)
13-14
11/95
12-13 11-12
Date 04/95
10-11 9-10 8-9 7-8 6-7 5-6
06/94
k)
4-5 3-4 2-3 1-2 0-1
09/93 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21
l)
Study Plot Fig. 6. 3D sequential graph showing grass cover over time.
when the population was in tropical Africa. Recorded in Gorham’s Cave. g) Magpie, Pica pica. This resident species is a ground dweller that is omnivorous and scavenges regularly. It was observed throughout open areas lacking dense vegetation where it could forage. A common species in the Gorham’s Cave fossil record. h) Jackdaw, Corvus monedula. The jackdaw, of similar habits to the magpie and often associated with it, exploited mainly the area of La Vera, and the edge of the marsh. It was more localised than the magpie and was not found in other parts of the study area. Another common species in Gorham’s Cave. i) Vultures, Gyps fulvus and Aegypius monachus. Vultures were only seen sporadically over the study area. These birds have ˜ ana bred and a very extensive range and those observed in Don
m)
n)
o)
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roosted on the cliffs that are located in the Sierra de Grazalema, some 100 km to the southeast. This probably explains the sporadic appearance of these birds. These vultures are recorded in the Gorham’s Cave fossil record. It is to be expected that, given the proximity of the cliffs of Gibraltar, their appearance in the coastal shelf habitats outside the cave would have been ˜ ana. more frequent than in present day Don ˜ ana, Azure-winged magpie, Cyanopica cyanus. A resident, in Don this species was detected in the fossil record in Gorham’s and Vanguard Caves. It was present throughout the study period. This bird is an excellent indicator of open stone pine (P. pinea) woodland. It was restricted mainly to the areas around study plots 10–15, and 19–20. These study plots are characterised by the presence of medium shrubs and low grass, each providing more than 25% cover, low and medium forbs, low shrubs, medium grass, bare ground, medium trees, low trees and high shrubs (in descending order) each with less than 25% cover. Red deer, C. elaphus (Fig. 8d). This species is frequent in the Gorham’s Cave record. Red deer are distributed across the ˜ ana landscape all year. The species has a wide habitat Don tolerance, occupying areas of dense shrub and margins of lakes and marsh, usually close to cover. Numbers were heavily concentrated with the onset of the heavy rains as suitable areas were lost through flooding. Fallow deer, D. dama. This species is not present in the fossil record in Gorham’s Cave, but its distribution patterns can give an indication of the movements of other large mammalian herbivores within this type of landscape. fallow deer were mostly observed in the marshes and in the area of La Vera, where there was ample grazing, although they were also found elsewhere. They were less restricted to vegetation cover than the red deer and were more regularly observed in the open. At the height of the wet period, when the marsh was covered with surface water, they were concentrated on available dry ground. Wild boar, S. scrofa. This species is also present in the fossil record in Gorham’s Cave. Boar are present throughout the area, but were observed mostly in the areas of the stabilised dunes, where there were denser shrublands than elsewhere. Its distribution does not appear to have been affected by the increase in rainfall. Horse, Equus caballus. The ‘Retuerta’ horse is allowed to roam in an almost feral state throughout the Biological Reserve, and is used in this study to illustrate the possible habits of the horses that have been recorded in the fossil record in Gorham’s Cave. Horses were observed mostly in La Vera and the lakes, always close to fresh water sources. Many would have been in the marsh away from the study area. During flooding these animals congregated on dry ground in La Vera. Cattle, Bos taurus. The ‘Mostrenca’ cattle are a feral population ˜ ana National Park, which may represent of cattle in the Don a remnant of a primitive cattle group in Western Europe dating to the 13th century (Alderson, 1992; Lazo, 1995). Whilst not the ˜ ana are included to give an same species, the cattle from Don idea of the possible movements of the Aurochs, Bos primigenius, present in the fossil record at Gorham’s Cave. Herds of the ‘Mostrenca’ were more concentrated in the landscape in those years immediately after increased rainfall, when the surface water levels were beginning to drop, but the grasses were still abundant in response to the higher water table.
4.4. Seasonal and between-year variability in bird species distribution
Fig. 7. 3D sequential graph showing species richness over time for all study plots. Light grey (low numbers) to dark grey (highest numbers).
The spatial response of different species throughout the year to seasonality and to the variability of the rainfall from year to year has been examined above, and each species can be seen to have
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a
b 0996
0996
0696
0696
0396
0396
1295
1295
0995
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0695
0695 0395
1294
1294
0994
0994
0694
0694
0394
0394
1293
1293 0993
0993 1
3
5
7
9
Date
Date
0395
1
11 13 15 17 19 21
3
5
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11 13 15 17 19 21
Study Plot
Study Plot
c 0996 0696 0396 1295
d
0995
1096
0695
0796
Date
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0496 0196
0994
1095
0694
0795
0394
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0195
0993 1
3
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11 13 15 17 19 21
Study Plot
Date
1294
1094 1
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11 13 15 17 19 21
Study Plot
Fig. 8. (a) Number of greylag geese, Anser anser, observed in Don˜ana transect. (b) Number of red-legged partridge, Alectoris rufa, observed in Don˜ana transect. (c) Number of quail, Coturnix coturnix, observed in Don˜ana transect. (d) Number of red deer, Cervus elaphus, observed in Don˜ana transect.
responded in distinct ways. In this section, the effect of variability in rainfall between years and within each year is explored further. For this part of the study, the number of individuals recorded for each species is expressed as a percentage of the highest number
recorded for that species throughout the study period, in order to facilitate comparison of species that differ in abundance. The start of the study coincided with the height of a drought, which had started after October 1991, and which finally broke in
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December 1995. The data collected therefore give a good indication of the effects of low rainfall, as well as the ensuing response to the rains. Bird species can be grouped into four main categories for this purpose (Finlayson, 2006): a) Those that responded favourably to the increase in the presence of surface water when the rains arrived, either directly in the water or on the edge of the marsh. b) Those that responded indirectly through the effects of the rains on grasses and insects. c) Those that were adversely affected by the increase in surface water, or by the increase in the depths of the lakes. d) Those that were not directly affected or which displayed no apparent response. This last category is made up of those bird species which were either not apparently affected by the change in rainfall, or which appeared to respond but the reasons for which are not clear. This group can be further subdivided into: residents not affected, Mediterranean wintering migrants affected, Mediterranean wintering migrants not affected, and trans-Saharan migrants not affected. Some of these species may have been responding to changes in areas outside the study area. 4.5. Variability in biomass during the study period In order to assess the productivity of the environment and to obtain a measure of the relationship between birds, as a category of ˜ ana, the relaconsumers, and the fluctuating environment of Don tionship with biomass was considered. To determine biomass, a database of bird weights was created from published sources (Cramp, 1977–1994). In order to obtain a close relationship with the energy flowing from the system these weights were transformed in accordance with the formula:
Energy Exp ¼ 4:1W 0:751
(1)
where W is weight and the Energy Exp is measured in watts. This is a generalised equation that predicts standard metabolic rate of homeotherms from fresh body mass (Peters, 1983). The results, an estimate of ‘consumer biomass’, give an indication of the area’s productivity. The total bird biomass expressed as a percentage of the highest value (5,237,497W) for the study period, was plotted against the PWI (Fig. 9). The high figure for the biomass in the
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winter of 1993/1994 may be attributable to the rains in the autumn of 1993, which came after four months in which only 10.8 mm of rain was recorded. This would account for the low PWI recorded at the start of study period despite these rains, but there would have been an effect on growth of vegetation. The next winter had a lower biomass because it followed from an earlier dry year. This suggests that there were cumulative effects operating in the system. The overriding factor in the percentage biomass curve is the seasonal increase in bird biomass resulting from the arrival of the wintering geese (A. anser) – the maximum value for this species was 4,741,427 W. This represents 90.5% of the total maximum bird biomass recorded. The fall in biomass for the year with the large increase in PWI can be attributed to the unavailability of grazing areas for the geese. These birds depend on open tracts of grassland for feeding, and with the extension of the water film over vast areas; their feeding grounds were very much reduced during the winter of 1995/1996. Closer study of the biomass curves for selected species or groups of species provides further detail as the data were not swamped by the values for the geese. Not all species are illustrated graphically. a) Herons and other related species feeding on fish and amphibians. This first group comprises predators that feed on fish and amphibians and are therefore dependent on the presence of standing water. They include cattle egret, Bubulcus ibis, little egret, Egretta garzetta, night heron, Nycticorax nycticorax, grey heron, Ardea cinerea, purple heron, Ardea purpurea, spoonbill, Platalea leucorodia, glossy ibis, Plegadis falcinellus, white stork, Ciconia ciconia, and black stork, Ciconia nigra. All, with the exception of the cattle egret, also belong to the group of species that benefit directly from the increase in water index, or from the extension of the marsh edge. These species displayed a strong seasonality throughout the study period, related to the establishment of breeding colonies (Fig. 10). The increase in biomass in the drought years may be attributable to a concentration of individuals within those lakes with water still remaining. However, the highest biomass was recorded for the year with the highest rainfall. The reproductive output was reflected by the second biomass peak in late summer which was not observed in the previous years.
100 120
Biomass (%) Water Index (%)
90
Total Biomass Water Index (%)
80
100
70 60
(%)
(%)
80
60
50 40 30
40
20 20
10
6 99
6 39
5 99
5 39
4 99
39
3 99 6 99
6 39
5 99
5 39
4 99
4 39
3 99
4
0 0
Date Fig. 9. Percentage of bird consumer biomass (max ¼ 5,237,497W) vs. Percentage Water Index (PWI) throughout the study period.
Date Fig. 10. Percentage biomass (max ¼ 456,920W) for Bubulcus ibis, Egretta garzetta, Nycticorax nycticorax, Ardea cinerea, Ardea purpurea, Platalea leucorodia, Plegadis falcinellus, Ciconia ciconia and Ciconia nigra, and the PWI throughout the study period.
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b) Bird species feeding among grasses. These species, whether feeding on seeds or on the insects that accumulate around them, were grouped and their combined biomass expressed as a percentage of the highest value. The data were plotted against the PWI and also the combined grass scores (also expressed as a percentage of the highest value). The species are quail, C. coturnix, turtle dove, Sterptopelia turtur, calandra lark, Melanocorypha calandra, short-toed lark, Calandrella brachydactyla, skylark, Alauda arvensis, fan-tailed warbler, Cisticola juncidis, house sparrow, Passer domesticus, and corn bunting, Emberiza calandra. These species also showed a slight increase during the breeding seasons throughout the study period, but there was a huge increase in their biomass coinciding with the rains. There was also an increase in numbers in the months that followed the rains, when the PWI had lowered substantially but there was a flush of grass. c) Ducks and other waterbirds This third group comprises species that feed on the water such as ducks and moorhens. This group is made up of mallard, Anas platyrhynchos, teal, Anas crecca, gadwall, Anas strepera, wigeon, Ana Penelope, pintail, Anas acuta, garganey, Anas querquedula, shoveler, Anas clypeata, pochard, Aythya farina, red-crested pochard, Netta rufina, moorhen, Gallinula chloropus, coot, Fulica atra, and purple gallinule, Porphyrio porphyrio. Some of these species were winter visitors, and some such as mallard were resident. The results for 1994 and 1995 show an increase in percentage biomass, coinciding with a lower PWI, due to the birds being concentrated within those areas that still had some standing water remaining. In 1996 when the PWI was at its highest, these birds were able to disperse over a wider area, beyond the study area, and this caused an apparent lowering in the percentage biomass. Many of these ducks are surface feeders that require shallow waters. d) Resident species not directly affected The percentage biomass curve for red-legged partridge A. rufa was plotted against the PWI and the percentage total grass score to illustrate one example of a species that was not apparently affected by the drought or increase in rainfall. Although there was a slight decrease in the percentage biomass attributable to the reduced feeding areas for this species during the period of highest PWI, the variations in the observations cannot be attributed only to the fluctuations in surface water or to the amount of grass present in the study area. ˜ ana and Gorham’s Cave 5. Don Finlayson (2006) argued that the habitats and landscapes of ˜ ana resemble those of the coastal plains off Gorham’s Cave. This Don was reinforced by estimates of vegetation structure at habitat and landscape levels for the environment outside Gorham’s Cave with corresponding predictions for the current bird community at ˜ ana (Finlayson, 2006). Both Don ˜ ana and the Gorham’s landDon scape occupy an intermediate position between dense forest and open plain. ˜ ana plots show that habitats and The results from the 21 Don landscapes with the vegetation, structural and bioclimatic characteristics described are biologically rich, highly seasonal, patchy and inter-annually unpredictable. The rainfall regime acts as the major ecological limiting factor – more so than temperature. It would appear reasonable to expect the emerged sandy coastal plains off ˜ ana, to Gorham’s Cave, with a similar bioclimatic regime to Don have behaved in a similar manner. This allows us to draw a picture
of the environment exploited by Neanderthals. It was a rich environment in which a great diversity and biomass of food resources were available seasonally, often in predictable locations. The climatic vicissitudes, similar to today’s or perhaps more accentuated, also made it an environment that would be seasonally, during the summer dry season, and inter-annually, during periods of severe drought, highly stressful. This implies that Neanderthals were intelligent humans with a capacity to survive in rich but highly unpredictable environments within a Mediterranean bioclimatic context. The presence of a diversity of habitats within a small area, generating mosaics and ecotones in space and time, may well have been a major factor permitting the late survival of the Neanderthals at Gorham’s Cave. The overriding influence of water-drought regimes, in an otherwise mild climate, suggests that water shortage would have been a greater problem than food shortage for the Neanderthals. If so, it is tempting to suggest that their survival was heavily dependent on annual rainfall and the presence of water sources. The combined evidence presented here, along with the range of fossil amphibians and reptiles, indicative of ephemeral water sources in sand dune areas (Finlayson, 2006), would seem to point to water, a hitherto largely ignored variable in palaeoanthropological studies, as the critical resource for Neanderthals living in an environment otherwise rich in a range of foods. Acknowledgements We thank the Director and staff of the Estacio´n Biolo´gica de ˜ ana, and all colleagues who have supported us in various Don aspects of the fieldwork. We are especially grateful to J S Carrio´n, D A Fa, F Giles-Pacheco, and to J Rodrı´guez-Vidal for their very useful and supportive discussions on the ideas contained in this paper and for their companionship in the field. Elements of the research carried out for this paper was carried out as part of the work for a Ph.D. thesis under Anglia Ruskin University. References Alderson, L., 1992. The categorisation of types and breeds of cattle in Europe. Archivos de Zootecnia 41, 325–334. Cramp, S. (Ed.), 1977–1994. Handbook of the Birds of Europe, the Middle East and North Africa: the Birds of the Western Palearctic, vols. 1–9. Oxford University Press, Oxford. Finlayson, G., 2006. Climate, vegetation and biodiversity – a multiscale study of the south of the Iberian Peninsula. Unpublished Ph.D. Thesis, University of Anglia Ruskin, UK. Finlayson, G., Finlayson, C., Giles Pacheco, F., Rodriguez Vidal, J., Carrio´n, J.S., Recio Espejo, J.M., 2007. Caves as archives of ecological and climatic changes in the Pleistocenedthe case of Gorham’s Cave, Gibraltar. Quaternary International 181 (1), 55–63. Finlayson, C., Fa, D.A., Jime´nez Espejo, F., Carrio´n, J.S., Finlayson, G., Giles Pacheco, F., Rodrı´guez Vidal, J., Stringer, C., Martı´nez Ruiz, F., 2008. Gorham’s Cave, Gibraltardthe persistence of a Neanderthal population. Quaternary International 181 (1), 64–71. Garcı´a Novo, F., Ramı´rez Dı´az, L., Torres Martı´nez, A., 1975. El sistema de dunas de Don˜ana. ICONA, Ministerio de Agricultura, Madrid. Kerr, J.T., Packer, L., 1997. Habitat heterogeneity as a determinant of mammal species richness in high-energy regions. Nature 385, 252–254. ˜ ana National Lazo, A., 1995. Ranging behaviour of feral cattle (Bos taurus) in Don Park, S.W. Spain. Journal of Zoology 236, 359–369. Peters, R.H., 1983. Cambridge Studies in Ecology: the Ecological Implications of Body Size. Cambridge University Press, Cambridge. ˜ a. Rivas-Martı´nez, S., 1987. Memoria del mapa de series de vegetacio´n de Espan 1:400,000. ICONA, Madrid. ˜ ez Camach, C., Gasco´, C., Clemente Salas, L., Anto´n, Ma.P., Rodrı´guez Ramı´rez, A., Yan 2005. Colmatacio´n Natural y Antro´pica de las Marismas del Parque Nacional de Don˜ana: Implicaciones para su Manejo y Conservacio´n. Revista Cuaternario y Geomorfologı´a 19 (3–4). Stevenson, A.C., 1985. Studies in the vegetational history of S.W. Spain. I. Modern ˜ ana National Park, Huelva. Journal of Biogeography 12, pollen rain in the Don 243–268.
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Dynamics of a thermo-Mediterranean coastal environment – the Coto ˜ ana National Park Don Geraldine Finlayson a, *, Clive Finlayson a, b, J.M. Recio Espejo c a
The Gibraltar Museum, 18–20 Bomb House Lane, Gibraltar Department of Social Sciences, University of Toronto, Scarborough Campus, Toronto, Canada c ´ rdoba, Co ´rdoba, Spain Departamento de Ecologia, Universidad de Co b
a r t i c l e i n f o
a b s t r a c t
Article history: Received 27 March 2008 Received in revised form 23 July 2008 Accepted 1 August 2008
Using data collected from existing habitats found in the southwestern Iberian Peninsula, and including ˜ ana, Spain, this study considers the data collected in the Biological Reserve of the Parque Nacional de Don seasonal and inter-annual variability of a thermo-Mediterranean, subhumid, environment and the significance of the presence of surface water in the system. This extant environment is then used together with the fossil record from Gorham’s Cave in Gibraltar, where Neanderthals lived, as a proxy for the ecology of the emerged landscape outside the cave. Ó 2008 Elsevier Ltd. All rights reserved.
1. Introduction The southern Iberian coastal site of Gorham’s Cave, Gibraltar, has been recently shown to have been a refuge for a number of species and the last known site of Neanderthal survival (Finlayson, 2006; Finlayson et al., 2008). The habitat outside Gorham’s Cave during the period of the last Neanderthals (32–24 ka) has been reconstructed using data from charcoal remains, pollen and bird remains within the stratigraphy of the site (Finlayson, 2006; Finlayson et al., 2007). The dominant habitat is an open woodland ‘savannah’ with patches of denser woodland and thickets. The thermophilous stone pine, Pinus pinea, is the main component of an essentially thermo-Mediterranean, subhumid, environment. This paper analyses an analogous coastal landscape that can be found today on the southwestern coast of Iberia (Fig. 1). The Bio˜ ana, Huelva (Spain), logical Reserve of the Parque Nacional de Don was the subject of a three-year study, from September 1993 to September 1996, which investigated the seasonal dynamics of birds and vegetation. The data presented in this paper provide information on seasonality as well as between-year variation, as a proxy for the environment in which the last Neanderthals lived. 2. Methods The study was carried out during monthly visits to the Reserve. On each of these visits, surveys were spread out over a two-day period. Twenty-one study plots were selected at intervals of 0.5 km,
* Corresponding author. E-mail address: [email protected] (G. Finlayson). 0277-3791/$ – see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.quascirev.2008.08.031
and a one-hectare sample within each study plot was divided into six separate zones. These plots were part of a wider Iberian survey that sampled a total of 980 plots (Finlayson, 2006). In each plot, birds were recorded between sunrise and the end of the morning activity; and the second day was dedicated to completing the bird census, when necessary, and to the vegetation survey. A record was also kept of the mammals observed during the standard sampling period (Finlayson, 2006; Finlayson et al., 2007). The largely undisturbed Biological Reserve was ideal for monitoring the distribution of birds and mammals (Finlayson et al., 2007). 3. Regional setting – the study site ˜ ana National Park are located within the The marshes of the Don delta of the Guadalquivir River between 6150 –6 300 W and 36 500 – 37100 N. Intense human activities have caused extensive modifications so that since the end of the 19th century, when the marsh area encompassed 140,000 ha, it had been reduced in 1996 to only 30,000 ha of virtually untouched habitats. These habitats form the strictly protected Biological Reserve that was the area chosen for the study (Finlayson, 2006). The marshes are the result of the progressive evolution of the ancient estuary of the Guadalquivir River, being cut off from the sea ˜ ana and Algaida) which have by a sand barrier of mobile dunes (Don been built up throughout the Holocene. The area can be divided into three distinct zones, or geological units: the ancient depression, of tectonic origin, now silted up with deltaic deposits from the river, the large coastal plain locally covered with aeolian sands (las arenas) and the sand barrier (Stevenson, 1985; Rodrı´guez Ramı´rez et al., 2005). The marsh (‘La Marisma’) covers 20,000 ha inside the Park. The dune system is composed of stabilised dunes, which form a series of
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Pistacia lentiscus, Monte negro woodland including Olea europaea and Quercus suber and usually associated with a parkland environment, Monte negro hygrophytic woodland, the wettest of the monte negro woodlands with a higher incidence of Q. suber, Myrtus communis, Pyrus bourgeana also present, and a dense and often impenetrable understorey containing Arbutus unedo, Smilax aspera, Rubia peregrina and Lonicera periclymenum, and Tamarix type, dominated by Tamarix africana, Tamarix canariensis and Populus alba. Fraxinus angustifolia and T. africana are also present in a wetter variant of the Quercus communities.
Fig. 1. Map of the study area with the Don˜ana National Park highlighted by a square.
arched ridges (old dunes) separated by flat depressions (old slacks). The geomorphology is conditioned by the evolution of the fluvial system, which has carved out a series of elevated channels (paciles). These in turn delimit enclosed hollows (‘lucios’), which, given the shallow water tables, frequently flood, filled with temporary lakes and ponds (‘lagunas’). There are mobile dunes, which advance at the rate of 5–6 m yr1 (Garcı´a Novo et al., 1975). These separate the marsh from the sea, and are in turn prevented from proceeding inland by the ancient meanders of the river. Climate is extremely seasonal and rainfall can vary significantly, averaging 550 mm yr1, and ranging between lows of 300 mm in 1980 and 1994 and highs of over 900 mm in 1987 and 1995 (Fig. 3). The bioclimatic attribution of all the study plots is thermoMediterranean, subhumid (Rivas-Martı´nez, 1987; Finlayson, 2006). Bioclimatically, the study area is comparable with the coastal plains that existed outside Gorham’s Cave for much of the last glacial cycle (Finlayson, 2006; Finlayson et al., 2007). 3.1. Vegetation The study site encompasses three types of vegetation that correspond to the following three main geomorphological units (Stevenson, 1985). 3.1.1. Marsh vegetation Open with very low grasses and forbs. 3.1.2. Stabilised dune vegetation Stevenson (1985) recognised three main succession groups, dependent on the depth of the water table: a) Grasslands, normally associated with areas where there is intensive grazing (e.g. by wild boar, Sus scrofa, fallow deer, Dama dama, or red deer, Cervus elaphus). b) Shrublands. These are characterised by three types of vegetation – the monte blanco which is the driest of the three with Lavandula stoechas, Helichrysum angustifolium, Halimium commutatum and Halimium halimifolium, the monte negro, characterised by the presence of Stauracanthus genistoides, H. halimifolium and Calluna vulgaris, and the monte negro hygrophytic shrubland, which is the wettest of the three and is dominated by Erica scoparia, but which also has the more drought sensitive Erica ciliaris, Ulex minor, Saccharum ravennae and Imperata cylindrica. c) Woods. These can also be subdivided into four different types according to the depth of the water table – Monte blanco woodland, which is the driest of the four, characterised by the presence of Juniperus phoenicea or Juniperus oxycedrus and
3.1.3. Mobile dune vegetation Vegetation here is dependent on the speed of movement of the dunes and the depth of the water table, and there are large areas of bare sands. The main shrub species is Corema album and the main tree species P. pinea, which is the only tree species that matures fast enough to keep pace with the movement of the dunes. The dune slacks are vegetated with Halimium spp. and P. pinea. ˜ana as a proxy for the Gorham’s Cave Neanderthal 3.2. Don environment The main plant taxa identified in the charcoal and pollen record in Gorham’s Cave are P. pinea, Juniperus spp., Quercus spp. (evergreen), Cistus–Halimium spp. and Erica spp. This particular combination is rare in any of the 980 1-ha study plots that have been investigated across the southwestern Iberian Peninsula (Finlayson, 2006), and in the present study (Table 1). ˜ ana Landscape Square are bioAll 21 study plots in the Don climatically thermo-Mediterranean, subhumid, whereas only 176 study plots (17.59%) out of the total analysed in Finlayson, 2006 fall into this bioclimatic zone of which 34.09% were those within ˜ ana (Finlayson et al., 2007). Don P. pinea is very locally distributed across much of southwestern Iberia, with only 87 (8.88%) out of the 980 study sites registering this species (Finlayson, 2006). Furthermore, the distribution of P. pinea is largely restricted to coastal areas. In the ˜ ana National Park, this 60 study plots that fell within the Don species is present in 20% of all plots. In the Biological Reserve it occupied 58% of the selected 21 plots. Likewise, compared to their representation in the 980 southwestern Iberian plots, Juniperus, Halimium and Erica are present in above average numbers ˜ ana (Table 1). in Don Given the uniqueness of these conditions within southwestern Iberia, and as a result of the high level of protection afforded to ˜ ana, we consider that the area of the Don ˜ ana National Park, Don and more specifically the Biological Reserve, is one of the few remaining zones within Iberia that can be used as a proxy for the habitats and landscapes that were located in the zone of the emerged shelf that existed outside Gorham’s Cave for much of the late Pleistocene.
Table 1 The frequency of the main plants identified in the Gorham’s Cave stratigraphy across ˜ ana. southwest Iberia and in Don
Pinus pinea Juniperus spp. Halimium spp. Quercus suber Cistus spp. Erica spp.
Presence in southwest Iberia (out of 980 study plots)
Frequency
Presence in ˜ ana (out of Don 60 study plots)
Frequency
87 85 56 216 234 67
8.88% 8.67% 5.71% 22.04% 23.88% 6.84%
12 6 18 3 9 15
20% 10% 30% 5% 15% 25%
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4. Results and discussion 4.1. Habitat structure Vegetation structure variables for grass, shrubs and trees are mapped as a 3D sequential graph to illustrate the spatial distribution of habitat variability (Fig. 2), along a transect which includes the ‘La Vera’ zone at the edge of the marsh (or ‘La Marisma’), the sands (‘las arenas’) and the area of the old dunes with temporary ponds and lakes (‘lagunas’). Study plots 1–7 on La Vera have virtually no trees and very few shrubs, but a presence of low and medium grasses. Towards the area of the old dunes – study plots 8–11 – the habitat changes with a greater abundance of medium and low shrubs, scattered trees, and very few grasses. Another change is apparent in study plot 12 with the presence of more trees and high shrubs, and an increase in grasses, including high grasses, which can be attributed to the higher water table in the area of the ponds and lakes. 4.2. Seasonality and between-year variability The study period covered an interval of intense drought following a period of heavy rainfall in 1989/1990 and gave way to a year with relatively high rainfall. Intense seasonal fluctuations as well as inter-annual variability in rainfall were therefore recorded during the study period (Fig. 3). The rainfall data available were then used to allocate an ombrotype for each year to show the variability from one year to the next. A Water Index (WI) – an estimate of standing water observed in each plot – was recorded, using a score based on the surface area covered by standing water, varying from 0 (no water) to 4 (>75% of surface with water). The scores for the six points in each plot were summed to give the PWI for the plot. Scores for all plots show a close relationship (R2 ¼ 0.718, p < 0.0001) with total rainfall recorded at the Palacio weather station (Fig. 4), demonstrating the validity of the water index as an easily obtained measure of water availability that can be plotted to show fine-scale variations in time and space (Fig. 5).
Fig. 2. Habitat structure of Don˜ana Biological Reserve transect. In this sequential plot, the values for each study plot are shown on the x-axis, and the vegetation sub-category along the y-axis. Shades refer to density of vegetation structural variables from grey (absent) to black (highest density). Categories were assigned as follows: grasses above 2 m GRAHI, those between 0.25 m and 2 m high GRAME, and those below 0.25 m in height GRALO. Shrubs above 2 m in height SHRHI, those between 0.25 m and 2 m tall SHRME and those up to 0.25 m SHRLO. Trees above 6 m TREHI, those between 2 m and 6 m TREME, and those below 2 m in height TRELO.
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A measure of variability in time and space was provided by the zone around plots 16 and 17 that often had some surface water present, but only on a seasonal basis, and the area became dry during the summer drought each year. The increase in rainfall commencing in January 1996 caused a marked increase in the amount of surface water present along the transect, and water persisted in the area of the lakes even throughout the summer drought of that year. The area of La Marisma/La Vera and a zone of temporary pools (plots 10–13), that had previously been dry throughout, also flooded. Spatio-temporal variation in vegetation features has been plotted in a similar manner (Fig. 6). Some features, such as trees, clearly changed little in the timescales involved. Changes in grasses were, however, notable, and this would be expected to have a significant impact on mammalian herbivores and grassland birds. Areas with grasses increased substantially in the wet period in 1996 but other areas showed a decrease in grass cover because standing water took over the zones where the grasses would normally be present. In general, there were some areas (e.g. plots 2–3, 5–6, 11– 12, 16–18) that favoured the development of grass cover, while other areas, covered by dense thickets (e.g. 8–10), only had grass cover after the heaviest rains. An estimate of bird species richness was obtained directly from the number of bird species present in each study plot. This was compared over time in the same type of 3D sequential graph (Fig. 7). Species richness was consistently highest in study plots 1– 7, which correspond to La Vera but even here the seasonality of the distribution was observed in a marked decrease of species richness during the summer drought. This richness in areas of ecological transition (ecotones) is well known (e.g. Kerr and Packer, 1997) and is clearly corroborated by this example. Seasonality was even more pronounced in study plots 10–13 and 15–19, which correspond to shrubland and lake areas, respectively. 4.3. Animal movements across the landscape over time The patchy distribution of water and plants over space and time is evident from Section 4.2. It gives an indication of the spatio-temporal patchiness of the kind of landscape that would have been used by prehistoric hunter-gatherers outside Gorham’s Cave during the last glacial cycle. We can take the comparison a stage further by looking at the distribution of birds and mammals in the same landscape. This permits inferences about ecosystem dynamics pertinent to the emerged coastal shelf of southern Iberia during the last glacial cycle. Ten species, or groups of species, of birds, and five species of large mammals were selected for analysis. The large mammals are ˜ ana. The birds chosen are taxa the principal species present in Don that are large and typical of the environment sampled. They are species that, in a prehistoric landscape (such as Gorham’s Cave), would have been significant to humans either as prey or as scavengers indicating the location of food sources. Although the analysis could have been conducted for other species, e.g. small insectivorous birds, these were not considered important in the context of the present study, and only selected species discussed below are illustrated graphically. a) Greylag goose, Anser anser (Fig. 8a). These birds are regular winter visitors and rely on grazing along the edges of the wetland. The seasonal concentration of these birds along La Vera is evident. The numbers were, paradoxically, lowest in the wettest winter. This reflected extensive flooding of grazing areas, forcing the birds to move to other zones of the Park or beyond. During the drought winters many carcasses of geese were observed in the dry Marismas. b) Ducks, Anas spp. Anas spp. were associated with the lakes and ponds, although they were also detected in La Vera. The
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450.00 Series1 400.00
Monthly Rainfall (mm)
350.00 300.00 250.00 200.00 150.00 100.00 50.00
M
79 S7 9 M 80 S8 0 M 81 S8 1 M 82 S8 2 M 83 S8 3 M 84 S8 4 M 85 S8 5 M 86 S8 6 M 87 S8 7 M 88 S8 8 M 89 S8 9 M 90 S9 0 M 91 S9 1 M 92 S9 2 M 93 S9 3 M 94 S9 4 M 95 S9 5
0.00
Date Fig. 3. Monthly rainfall recorded at the Palacio Don˜ana from October 1978 to January 1996.
presence of Anas spp. was highly seasonal, although as in the case of Anser, these too were negatively affected by the rainfall. The reason is that many of these ducks are surface feeders in shallow water and excessive water makes lakes and pools unsuitable. For these birds, and for the geese, intermediate rainfall years (neither too dry nor too wet) appeared optimal. c) The Red-legged partridge, Alectoris rufa (Fig. 8b) This is a seedeater and was present throughout the year and throughout the study area. Although it was most common in La Vera, it was also observed regularly near the lakes and ponds. Its presence did not appear to be affected by rainfall. Fewer birds were observed in spring when breeding pairs were notoriously shy and skulking. This is an abundant species in the Gorham’s Cave deposits. d) Quail, Coturnix coturnix (Fig. 8c). Quails are trans-Saharan migrants. They arrive to breed in the Park from tropical Africa in the spring. This species was only observed during the years of high rainfall, and they were present in both the area of La
Vera as well as the area of the lakes and ponds. The presence of this species is therefore highly erratic depending entirely on years with exceptionally high rainfall, not breeding in years of drought. Its presence is related to the increase in grass cover following heavy rainfall. This is an abundant species in Gorham’s Cave. e) Red kite, Milvus milvus. This is a resident raptor and regular scavenger. It was sporadically observed, although mainly over La Vera and the stabilised dunes, but it was also recorded over the lakes. This is a regular species in the Gorham’s Cave sequence. f) Black kite, Milvus migrans. This species is a regular scavenger and predator of small mammals, birds and frogs. This summer visitor was observed more frequently than Red kite, M. milvus. It was more widely distributed but seasonally absent in winter
80 Series1 70
Water Index (%)
60 50 40 30 20 10 0 0.00
50.00
100.00
150.00
200.00
250.00
300.00
350.00
Rainfall (mm) Fig. 4. Regression of the percentage Water Index (WI%) against the monthly rainfall in the Don˜ana Biological Reserve.
Fig. 5. 3D sequential graph showing the distribution of standing water over time. Shades refer to amount of standing water present from light grey (absent) to dark grey (highest cover). (PWI represents the proportion of the highest WI recorded over the three years of the study).
G. Finlayson et al. / Quaternary Science Reviews 27 (2008) 2145–2152
06/96
17-18 16-17 15-16 14-15
j)
13-14
11/95
12-13 11-12
Date 04/95
10-11 9-10 8-9 7-8 6-7 5-6
06/94
k)
4-5 3-4 2-3 1-2 0-1
09/93 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21
l)
Study Plot Fig. 6. 3D sequential graph showing grass cover over time.
when the population was in tropical Africa. Recorded in Gorham’s Cave. g) Magpie, Pica pica. This resident species is a ground dweller that is omnivorous and scavenges regularly. It was observed throughout open areas lacking dense vegetation where it could forage. A common species in the Gorham’s Cave fossil record. h) Jackdaw, Corvus monedula. The jackdaw, of similar habits to the magpie and often associated with it, exploited mainly the area of La Vera, and the edge of the marsh. It was more localised than the magpie and was not found in other parts of the study area. Another common species in Gorham’s Cave. i) Vultures, Gyps fulvus and Aegypius monachus. Vultures were only seen sporadically over the study area. These birds have ˜ ana bred and a very extensive range and those observed in Don
m)
n)
o)
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roosted on the cliffs that are located in the Sierra de Grazalema, some 100 km to the southeast. This probably explains the sporadic appearance of these birds. These vultures are recorded in the Gorham’s Cave fossil record. It is to be expected that, given the proximity of the cliffs of Gibraltar, their appearance in the coastal shelf habitats outside the cave would have been ˜ ana. more frequent than in present day Don ˜ ana, Azure-winged magpie, Cyanopica cyanus. A resident, in Don this species was detected in the fossil record in Gorham’s and Vanguard Caves. It was present throughout the study period. This bird is an excellent indicator of open stone pine (P. pinea) woodland. It was restricted mainly to the areas around study plots 10–15, and 19–20. These study plots are characterised by the presence of medium shrubs and low grass, each providing more than 25% cover, low and medium forbs, low shrubs, medium grass, bare ground, medium trees, low trees and high shrubs (in descending order) each with less than 25% cover. Red deer, C. elaphus (Fig. 8d). This species is frequent in the Gorham’s Cave record. Red deer are distributed across the ˜ ana landscape all year. The species has a wide habitat Don tolerance, occupying areas of dense shrub and margins of lakes and marsh, usually close to cover. Numbers were heavily concentrated with the onset of the heavy rains as suitable areas were lost through flooding. Fallow deer, D. dama. This species is not present in the fossil record in Gorham’s Cave, but its distribution patterns can give an indication of the movements of other large mammalian herbivores within this type of landscape. fallow deer were mostly observed in the marshes and in the area of La Vera, where there was ample grazing, although they were also found elsewhere. They were less restricted to vegetation cover than the red deer and were more regularly observed in the open. At the height of the wet period, when the marsh was covered with surface water, they were concentrated on available dry ground. Wild boar, S. scrofa. This species is also present in the fossil record in Gorham’s Cave. Boar are present throughout the area, but were observed mostly in the areas of the stabilised dunes, where there were denser shrublands than elsewhere. Its distribution does not appear to have been affected by the increase in rainfall. Horse, Equus caballus. The ‘Retuerta’ horse is allowed to roam in an almost feral state throughout the Biological Reserve, and is used in this study to illustrate the possible habits of the horses that have been recorded in the fossil record in Gorham’s Cave. Horses were observed mostly in La Vera and the lakes, always close to fresh water sources. Many would have been in the marsh away from the study area. During flooding these animals congregated on dry ground in La Vera. Cattle, Bos taurus. The ‘Mostrenca’ cattle are a feral population ˜ ana National Park, which may represent of cattle in the Don a remnant of a primitive cattle group in Western Europe dating to the 13th century (Alderson, 1992; Lazo, 1995). Whilst not the ˜ ana are included to give an same species, the cattle from Don idea of the possible movements of the Aurochs, Bos primigenius, present in the fossil record at Gorham’s Cave. Herds of the ‘Mostrenca’ were more concentrated in the landscape in those years immediately after increased rainfall, when the surface water levels were beginning to drop, but the grasses were still abundant in response to the higher water table.
4.4. Seasonal and between-year variability in bird species distribution
Fig. 7. 3D sequential graph showing species richness over time for all study plots. Light grey (low numbers) to dark grey (highest numbers).
The spatial response of different species throughout the year to seasonality and to the variability of the rainfall from year to year has been examined above, and each species can be seen to have
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Fig. 8. (a) Number of greylag geese, Anser anser, observed in Don˜ana transect. (b) Number of red-legged partridge, Alectoris rufa, observed in Don˜ana transect. (c) Number of quail, Coturnix coturnix, observed in Don˜ana transect. (d) Number of red deer, Cervus elaphus, observed in Don˜ana transect.
responded in distinct ways. In this section, the effect of variability in rainfall between years and within each year is explored further. For this part of the study, the number of individuals recorded for each species is expressed as a percentage of the highest number
recorded for that species throughout the study period, in order to facilitate comparison of species that differ in abundance. The start of the study coincided with the height of a drought, which had started after October 1991, and which finally broke in
G. Finlayson et al. / Quaternary Science Reviews 27 (2008) 2145–2152
December 1995. The data collected therefore give a good indication of the effects of low rainfall, as well as the ensuing response to the rains. Bird species can be grouped into four main categories for this purpose (Finlayson, 2006): a) Those that responded favourably to the increase in the presence of surface water when the rains arrived, either directly in the water or on the edge of the marsh. b) Those that responded indirectly through the effects of the rains on grasses and insects. c) Those that were adversely affected by the increase in surface water, or by the increase in the depths of the lakes. d) Those that were not directly affected or which displayed no apparent response. This last category is made up of those bird species which were either not apparently affected by the change in rainfall, or which appeared to respond but the reasons for which are not clear. This group can be further subdivided into: residents not affected, Mediterranean wintering migrants affected, Mediterranean wintering migrants not affected, and trans-Saharan migrants not affected. Some of these species may have been responding to changes in areas outside the study area. 4.5. Variability in biomass during the study period In order to assess the productivity of the environment and to obtain a measure of the relationship between birds, as a category of ˜ ana, the relaconsumers, and the fluctuating environment of Don tionship with biomass was considered. To determine biomass, a database of bird weights was created from published sources (Cramp, 1977–1994). In order to obtain a close relationship with the energy flowing from the system these weights were transformed in accordance with the formula:
Energy Exp ¼ 4:1W 0:751
(1)
where W is weight and the Energy Exp is measured in watts. This is a generalised equation that predicts standard metabolic rate of homeotherms from fresh body mass (Peters, 1983). The results, an estimate of ‘consumer biomass’, give an indication of the area’s productivity. The total bird biomass expressed as a percentage of the highest value (5,237,497W) for the study period, was plotted against the PWI (Fig. 9). The high figure for the biomass in the
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winter of 1993/1994 may be attributable to the rains in the autumn of 1993, which came after four months in which only 10.8 mm of rain was recorded. This would account for the low PWI recorded at the start of study period despite these rains, but there would have been an effect on growth of vegetation. The next winter had a lower biomass because it followed from an earlier dry year. This suggests that there were cumulative effects operating in the system. The overriding factor in the percentage biomass curve is the seasonal increase in bird biomass resulting from the arrival of the wintering geese (A. anser) – the maximum value for this species was 4,741,427 W. This represents 90.5% of the total maximum bird biomass recorded. The fall in biomass for the year with the large increase in PWI can be attributed to the unavailability of grazing areas for the geese. These birds depend on open tracts of grassland for feeding, and with the extension of the water film over vast areas; their feeding grounds were very much reduced during the winter of 1995/1996. Closer study of the biomass curves for selected species or groups of species provides further detail as the data were not swamped by the values for the geese. Not all species are illustrated graphically. a) Herons and other related species feeding on fish and amphibians. This first group comprises predators that feed on fish and amphibians and are therefore dependent on the presence of standing water. They include cattle egret, Bubulcus ibis, little egret, Egretta garzetta, night heron, Nycticorax nycticorax, grey heron, Ardea cinerea, purple heron, Ardea purpurea, spoonbill, Platalea leucorodia, glossy ibis, Plegadis falcinellus, white stork, Ciconia ciconia, and black stork, Ciconia nigra. All, with the exception of the cattle egret, also belong to the group of species that benefit directly from the increase in water index, or from the extension of the marsh edge. These species displayed a strong seasonality throughout the study period, related to the establishment of breeding colonies (Fig. 10). The increase in biomass in the drought years may be attributable to a concentration of individuals within those lakes with water still remaining. However, the highest biomass was recorded for the year with the highest rainfall. The reproductive output was reflected by the second biomass peak in late summer which was not observed in the previous years.
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0 0
Date Fig. 9. Percentage of bird consumer biomass (max ¼ 5,237,497W) vs. Percentage Water Index (PWI) throughout the study period.
Date Fig. 10. Percentage biomass (max ¼ 456,920W) for Bubulcus ibis, Egretta garzetta, Nycticorax nycticorax, Ardea cinerea, Ardea purpurea, Platalea leucorodia, Plegadis falcinellus, Ciconia ciconia and Ciconia nigra, and the PWI throughout the study period.
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b) Bird species feeding among grasses. These species, whether feeding on seeds or on the insects that accumulate around them, were grouped and their combined biomass expressed as a percentage of the highest value. The data were plotted against the PWI and also the combined grass scores (also expressed as a percentage of the highest value). The species are quail, C. coturnix, turtle dove, Sterptopelia turtur, calandra lark, Melanocorypha calandra, short-toed lark, Calandrella brachydactyla, skylark, Alauda arvensis, fan-tailed warbler, Cisticola juncidis, house sparrow, Passer domesticus, and corn bunting, Emberiza calandra. These species also showed a slight increase during the breeding seasons throughout the study period, but there was a huge increase in their biomass coinciding with the rains. There was also an increase in numbers in the months that followed the rains, when the PWI had lowered substantially but there was a flush of grass. c) Ducks and other waterbirds This third group comprises species that feed on the water such as ducks and moorhens. This group is made up of mallard, Anas platyrhynchos, teal, Anas crecca, gadwall, Anas strepera, wigeon, Ana Penelope, pintail, Anas acuta, garganey, Anas querquedula, shoveler, Anas clypeata, pochard, Aythya farina, red-crested pochard, Netta rufina, moorhen, Gallinula chloropus, coot, Fulica atra, and purple gallinule, Porphyrio porphyrio. Some of these species were winter visitors, and some such as mallard were resident. The results for 1994 and 1995 show an increase in percentage biomass, coinciding with a lower PWI, due to the birds being concentrated within those areas that still had some standing water remaining. In 1996 when the PWI was at its highest, these birds were able to disperse over a wider area, beyond the study area, and this caused an apparent lowering in the percentage biomass. Many of these ducks are surface feeders that require shallow waters. d) Resident species not directly affected The percentage biomass curve for red-legged partridge A. rufa was plotted against the PWI and the percentage total grass score to illustrate one example of a species that was not apparently affected by the drought or increase in rainfall. Although there was a slight decrease in the percentage biomass attributable to the reduced feeding areas for this species during the period of highest PWI, the variations in the observations cannot be attributed only to the fluctuations in surface water or to the amount of grass present in the study area. ˜ ana and Gorham’s Cave 5. Don Finlayson (2006) argued that the habitats and landscapes of ˜ ana resemble those of the coastal plains off Gorham’s Cave. This Don was reinforced by estimates of vegetation structure at habitat and landscape levels for the environment outside Gorham’s Cave with corresponding predictions for the current bird community at ˜ ana (Finlayson, 2006). Both Don ˜ ana and the Gorham’s landDon scape occupy an intermediate position between dense forest and open plain. ˜ ana plots show that habitats and The results from the 21 Don landscapes with the vegetation, structural and bioclimatic characteristics described are biologically rich, highly seasonal, patchy and inter-annually unpredictable. The rainfall regime acts as the major ecological limiting factor – more so than temperature. It would appear reasonable to expect the emerged sandy coastal plains off ˜ ana, to Gorham’s Cave, with a similar bioclimatic regime to Don have behaved in a similar manner. This allows us to draw a picture
of the environment exploited by Neanderthals. It was a rich environment in which a great diversity and biomass of food resources were available seasonally, often in predictable locations. The climatic vicissitudes, similar to today’s or perhaps more accentuated, also made it an environment that would be seasonally, during the summer dry season, and inter-annually, during periods of severe drought, highly stressful. This implies that Neanderthals were intelligent humans with a capacity to survive in rich but highly unpredictable environments within a Mediterranean bioclimatic context. The presence of a diversity of habitats within a small area, generating mosaics and ecotones in space and time, may well have been a major factor permitting the late survival of the Neanderthals at Gorham’s Cave. The overriding influence of water-drought regimes, in an otherwise mild climate, suggests that water shortage would have been a greater problem than food shortage for the Neanderthals. If so, it is tempting to suggest that their survival was heavily dependent on annual rainfall and the presence of water sources. The combined evidence presented here, along with the range of fossil amphibians and reptiles, indicative of ephemeral water sources in sand dune areas (Finlayson, 2006), would seem to point to water, a hitherto largely ignored variable in palaeoanthropological studies, as the critical resource for Neanderthals living in an environment otherwise rich in a range of foods. Acknowledgements We thank the Director and staff of the Estacio´n Biolo´gica de ˜ ana, and all colleagues who have supported us in various Don aspects of the fieldwork. We are especially grateful to J S Carrio´n, D A Fa, F Giles-Pacheco, and to J Rodrı´guez-Vidal for their very useful and supportive discussions on the ideas contained in this paper and for their companionship in the field. Elements of the research carried out for this paper was carried out as part of the work for a Ph.D. thesis under Anglia Ruskin University. References Alderson, L., 1992. The categorisation of types and breeds of cattle in Europe. Archivos de Zootecnia 41, 325–334. Cramp, S. (Ed.), 1977–1994. Handbook of the Birds of Europe, the Middle East and North Africa: the Birds of the Western Palearctic, vols. 1–9. Oxford University Press, Oxford. Finlayson, G., 2006. Climate, vegetation and biodiversity – a multiscale study of the south of the Iberian Peninsula. Unpublished Ph.D. Thesis, University of Anglia Ruskin, UK. Finlayson, G., Finlayson, C., Giles Pacheco, F., Rodriguez Vidal, J., Carrio´n, J.S., Recio Espejo, J.M., 2007. Caves as archives of ecological and climatic changes in the Pleistocenedthe case of Gorham’s Cave, Gibraltar. Quaternary International 181 (1), 55–63. Finlayson, C., Fa, D.A., Jime´nez Espejo, F., Carrio´n, J.S., Finlayson, G., Giles Pacheco, F., Rodrı´guez Vidal, J., Stringer, C., Martı´nez Ruiz, F., 2008. Gorham’s Cave, Gibraltardthe persistence of a Neanderthal population. Quaternary International 181 (1), 64–71. Garcı´a Novo, F., Ramı´rez Dı´az, L., Torres Martı´nez, A., 1975. El sistema de dunas de Don˜ana. ICONA, Ministerio de Agricultura, Madrid. Kerr, J.T., Packer, L., 1997. Habitat heterogeneity as a determinant of mammal species richness in high-energy regions. Nature 385, 252–254. ˜ ana National Lazo, A., 1995. Ranging behaviour of feral cattle (Bos taurus) in Don Park, S.W. Spain. Journal of Zoology 236, 359–369. Peters, R.H., 1983. Cambridge Studies in Ecology: the Ecological Implications of Body Size. Cambridge University Press, Cambridge. ˜ a. Rivas-Martı´nez, S., 1987. Memoria del mapa de series de vegetacio´n de Espan 1:400,000. ICONA, Madrid. ˜ ez Camach, C., Gasco´, C., Clemente Salas, L., Anto´n, Ma.P., Rodrı´guez Ramı´rez, A., Yan 2005. Colmatacio´n Natural y Antro´pica de las Marismas del Parque Nacional de Don˜ana: Implicaciones para su Manejo y Conservacio´n. Revista Cuaternario y Geomorfologı´a 19 (3–4). Stevenson, A.C., 1985. Studies in the vegetational history of S.W. Spain. I. Modern ˜ ana National Park, Huelva. Journal of Biogeography 12, pollen rain in the Don 243–268.