Final Report Summary - P3LIG (People, prey and predators: Community dynamics in the Last Interglacial)
Executive Summary:
P3LIG tested the hypothesis that the internal dynamics of animal communities are at least as influential as external climatic processes in shaping large mammal faunas, using the European Last Interglacial as a case study. As a basis for the work carried out to achieve the objectives detailed below, faunal lists and environmental information for 81 Last Interglacial sites were collected and entered in a database. The sites are located in the area between 39°N and 55°N latitude and 5°W and 40°E longitude, with a few outlying sites included further north and east (up to 60°N and 58°E) for comparison. Only sites that are securely dated with absolute dating methods or by stratigraphic considerations were included in the study.
Objectives:
1. To develop food web models for fossil communities.
Extant European faunas contain a relatively low number of large mammals (>1 kg) due to the extinction of many Pleistocene forms at the end of the last ice age. Fossil communities encompassed a larger number of large and very large herbivore species, and as a consequence the number of carnivore species was larger too. As such, the fossil European faunal communities were more similar to present-day African faunas, although the environmental conditions were very different. During the Last Interglacial, the number of predator species and the species composition of the carnivore assemblages did not vary significantly across Europe, although the British Isles had a relatively low number of predators. In contrast, both the number of herbivores and their species composition did vary across Europe. This impacted on the structure of the food web, in particular when the British Isles with fewer herbivores are compared with the rest of Europe. For many archaeological sites, abundance data are not available, and taphonomic issues often prevent an assessment of past animal abundances from fossil remains. This hampers the reconstruction of past food webs, which are necessarily based on a generalisation of prey size preferences of extant carnivores.
2. To examine variations in faunal composition and behaviour in the context of environmental variables.
Using GIS, site coordinates and faunal lists for each sites, the geographic distribution for each species was analysed. Faunal variation was assessed in conjunction with site type to investigate the influence of depositional processes on faunal composition. Faunas from different site types did not differ significantly in species richness, although faunal diversity of the British Isles was clearly depleted regardless of site type.
To examine community structure, the large mammals present at each site were classified according to ecologically relevant variables. Each mammal species was grouped in one of six body size categories, one of three locomotor categories and one of four dietary categories. Together these categorisations give an indication of the habitat requirements and niches filled by the mammalian community. Cluster analysis indicated the absence of clear patterning in the distribution of species over the ecological categories across Europe. Community structure was therefore stable, corroborating the pollen evidence for the climatic homogeneity of Europe during the Last Interglacial. This pattern was further strengthened by the absence of differences across Europe in the hypsodonty index, which reflects precipitation levels and the level of openness of the vegetation. However, when presence/absence data for all species were compared across Europe, three different faunas could be distinguished: the fauna of the British Isles, the fauna of western continental Europe and the fauna of eastern continental Europe. This indicates that although the available niches were similar across Europe, the specific identity of the animals filling these niches varied between the different regions of Europe.
On a smaller scale, the distribution of certain species was connected with the occurrence of suitable habitats. Species adapted to mountain habitats only occurred in regions of higher elevation. Animals that tend to be more abundant during colder periods (woolly mammoth, woolly rhinoceros, reindeer) clustered in eastern and central Europe (Poland, Czech Republic, Hungary). These animals are not primarily adapted to cold climates, but to dry conditions. Their presence in this part of Europe indicates that this presently relatively dry part of Europe was also drier than the rest of Europe in the Last Interglacial. However, in some of these sites faunal material from later date may have been mixed in with the Last Interglacial material.
3. To assess dietary variation within herbivore and carnivore guilds using mesowear and microwear analyses.
4. To infer habitat preferences and investigate the role of competition from functional morphology using geometric morphometrics.
Objectives 3 and 4 were jointly addressed in a more detailed study of a particular group of animals: the rhinoceroses. This study expanded into a larger study carried out in collaboration with Prof. R.-D. Kahlke of the Senckenberg Forschungsstation für Quartärpaläontologie in Weimar, Germany. Additional funding through a Liverpool John Moores University Early Career Researcher Fellowship allowed for a visit to the fossil collections of the Senckenberg Forschungsstation. Funding from the German Academic Exchange Service made a second visit possible, while visits to Last Interglacial fossil assemblages in four museums and one private collection in the British Isles were funded by the Quaternary Research Association. The study also involved the collection of comparative data for the five extant rhinoceros species in three museums in Germany, France and Belgium.
At an early stage, after reviewing the literature, it was decided not to use microwear analysis since this technique gives insight into the short-term diet of fossils. For most sites it is unclear how much time is represented in the faunal assemblage, and fossils representing winter and summer diets may be mixed together. Mesowear, in contrast, gives a longer-term perspective on the diet.
During the Last Interglacial, two rhinoceroses adapted to temperate climates occurred in Europe: the steppe rhinoceros Stephanorhinus hemitoechus occurred mainly in western Europe, including the British Isles, whereas the forest rhinoceros S. kirchbergensis occurred mainly in central and eastern Europe. Both species had a mesowear signature characteristic of a mixed feeder. It is striking that both species are displaced towards the browser side of the spectrum, though S. kirchbergensis is closer to the browser side of the spectrum than S. hemitoechus. Morphometrically, the two species are clearly distinct, but these differences seem to be related primarily to body size differences between the two species. The project investigating competition between the species and variation within the species is ongoing.
5. To combine morphometric and palaeoecological analyses in a large-scale synthesis.
A synthesis of the results obtained under objectives 1-4 led to the conclusion that the European Last Interglacial faunas were shaped by a combination of external climatic processes and the internal dynamics of the animal communities. The distribution of some species was strongly affected by habitat characteristics. For instance, the cave bear was limited to mountainous areas with suitable caves for hibernation, and appears to have been unable to cross large areas of heavily forested lowlands. The distribution of other animals was contingent on historical factors. The disjunct distribution of the steppe rhinoceros and forest rhinoceros during the Last Interglacial was partly caused by the fact that during the preceding glacial, the steppe rhinoceros survived in the Iberian and Italian peninsulas, whereas the forest rhinoceros was confined to more easterly regions. As a consequence, when the climate warmed, the steppe rhinoceros could spread to northwestern Europe more easily. Finally, the distribution of several other species was influenced by the presence or absence of other species. The apparent absence of horses and hominins from the British Isles may be related to the higher predator pressure in this region due to the absence of several large prey species. Conclusions
External climatic processes exert a strong influence on mammalian species, in particular by limiting their distribution to areas with a climate to which they are well-adapted. Indirectly, climatic factors shape mammalian faunas through historical processes, such as the location of suitable habitats during phases of severe climate. However, the project has shown that internal dynamics of animal communities can also significantly affect mammalian community composition. Variations in predator-prey interactions, and concomitant variations in the structure of the food web, together with dispersal ability can lead to differences in the composition of faunas in geographical locations which are climatically similar. Thus, the application of concepts and methods from ecology can significantly enrich our understanding of patterns and processes in European fossil faunas.