New insights into palaeo-distributions based on Holocene rock art

Abstract

Aim: Due to the lack of sufficient information, with which to infer past distributions of species, Ecological Niche Modelling (ENM) has been used to reconstruct palaeo-distributions, based on projections of current species ecological niches onto past climatic scenarios. In this study, we utilized ENM to directly and independently reconstruct the Mid-Holocene distribution of the desert bighorn sheep, using rock art as an alternative source of past distributional information, in order to gain a better understanding of changes in the distribution of this species over the last 6,000 years. Location: North American deserts. Taxon: Desert bighorn sheep (Ovis canadensis nelsoni). Methods: We used 225 current locality records, eight bioclimatic variables from WorldClim and 57 past locality records based on rock art, in combination with CCSM4 and MIROC-ESM scenarios for the Mid-Holocene, to reconstruct via ENM the present and past ecological niches and geographic distribution of the species. For modelling ecological niches, we used Maxent, and the models were evaluated using a partial ROC test. We used a niche similarity test to compare present and past reconstructions, performing niche transfers to measure their inter-predictability, supported by a previous Mobility Oriented Parity test of climate analogy. Results: The performances of the potential distribution models for the Mid-Holocene and present were statistically significant and describe a recent increase in the species’ distributional areas, suggesting that past conditions were characterized by higher temperatures and lower precipitation, as was corroborated by the niche transfers. The niche similarity test showed no differences between the past and present niches. Main conclusions: The models generated from rock art allowed a consistent reconstruction of the ecological niches and present and past distributions of the species. We therefore consider rock art to be a valuable, but hitherto largely ignored, source of information for this species. Analysis of current and past distributions revealed how the species have responded to past climatic changes.