Mammal associations in the Pleistocene of Britain: Implications of Ecological Niche Modelling and a Method for Reconstrucing Palaeoclimate

The climatic envelope of a species is a multivariate space whose axes are climatic variables and whose boundaries are the upper and lower values of those variables that occur within the species’ geographic range. If climate limits the geographic ranges of species, then the climate envelope can be used to predict which ones will occur together in a palaeofauna or to reconstruct palaeoclimate based on the species found in a fossil site. We evaluated these possibilities using ten living mammal species, four that are now found in cold climates (Alopex lagopus, Lemmus lemmus, Ovibos moschatus and Rangifer tarandus), three that are now found in warm climates (Crocuta crocuta, Panthera leo, and Hippopotamus amphibius), and three that are broadly spread through temperate climates (Arvicola terrestris, Cervus elaphus, and Sus scrofa). The WorldClim dataset of 19 climatic variables was used to characterize climate distributions for the 10 species. Out of the 45 possible pairings of the 10 species, 22 pairs have geographic ranges that do not overlap, but only 12 pairs have climatic envelopes that do not overlap. We looked at 22 palaeofaunas from the British Quaternary palaeofauna: 44% of them had species whose climatic envelopes do not overlap today (these are climatically ‘non-analogue’ or ‘disharmonious’ faunas), whereas 82% of the faunas had species whose geographic ranges do not overlap (these are geographically non-analogue faunas). The ‘index of disharmony’ (IR) was IR = 0.38 when geographic non-overlap was used as a criterion (higher than in similar aged North American faunas) but only IR = 0.12 when climatic non-overlap was used. A maximum-likelihood function was used to estimate the most probable climate for the 22 palaeofaunas based on the modern climatic distribution of the 10 species. The reconstructions were generally compatible with other quantitative estimates of palaeoclimate at the same sites.