Late Quaternary habitat suitability models for chimpanzees (Pan troglodytes) since the Last Interglacial (120,000 BP)

Abstract

AimPaleoclimate reconstructions have enhanced our understanding of how past climates may have shaped present-day biodiversity. We hypothesize that habitat stability in historical Afrotropical refugia played a major role in the habitat suitability and persistence of chimpanzees (Pan troglodytes) during the late Quaternary. We aimed to build a dynamic model of changing habitat suitability for chimpanzees at fine spatio-temporal scales to provide a new resource for understanding their ecology, behaviour and evolution.LocationAfrotropics.TaxonChimpanzee (Pan troglodytes), including all four subspecies (P. t. verus, P. t. ellioti, P. t. troglodytes, P. t. schweinfurthii).MethodsWe used downscaled bioclimatic variables representing monthly temperature and precipitation estimates, historical human population density data and an extensive database of georeferenced presence points to infer chimpanzee habitat suitability at 62 paleoclimatic time periods across the Afrotropics based on ensemble species distribution models. We mapped habitat stability over time using an approach that accounts for dispersal between time periods, and compared our modelled stability estimates to existing knowledge of Afrotropical refugia. Our models cover a spatial resolution of 0.0467 degrees (approximately 5.19 km2 grid cells) and a temporal resolution of every 1,000–4,000 years dating back to the Last Interglacial (120,000 BP).ResultsOur results show high habitat stability concordant with known historical forest refugia across Africa, but suggest that their extents are underestimated for chimpanzees. We provide the first fine-grained dynamic map of historical chimpanzee habitat suitability since the Last Interglacial which is suspected to have influenced a number of ecological-evolutionary processes, such as the emergence of complex patterns of behavioural and genetic diversity.Main ConclusionsWe provide a novel resource that can be used to reveal spatio-temporally explicit insights into the role of refugia in determining chimpanzee behavioural, ecological and genetic diversity. This methodology can be applied to other taxonomic groups and geographic areas where sufficient data are available.

Chimpanzees (Pan troglodytes) in savanna landscapes

“…Lower population densities on savannas are somewhat consistent with the ideas that P. troglodytes is a forest‐adapted or forest‐suited species 150,151 and that savanna chimpanzees represent population sinks that are supported by immigrants from forest‐population sources 150–152 . A problem with this logic, however, is that population density comparisons alone are insufficient for identifying sources and sinks 153–155 .…”

Population dynamics and genetic connectivity in recent chimpanzee history

“… 59 The higher inter-connectivity of western chimpanzees may also help to explain their larger behavioral diversity compared with non-western chimpanzee populations. A large degree of sharing of IBD-like fragments in the northwestern range of western chimpanzees, resulting from either recent expansion or high recent connectivity, might reflect population movements from Pleistocene refugia in the south (Liberia, Côte d’Ivoire) after the LGM ( Figure 2 B), 12 , 13 possibly related to the proposed cultural expansion in western chimpanzees. 14 However, the Comoé sites in the east of Côte d’Ivoire are genetically closer to forest populations in the south ( Figures S45 and S54 ), despite seemingly being behaviorally similar to the north-eastern mosaic woodland habitat populations.…”

“… 1 , 10 , 11 This long-standing question also relates to the degree of connectivity among subspecies over time, which requires a fine-scaled reconstruction of the demographic history of chimpanzee populations after their split more than ∼100 thousand years ago (kya) 6 and their inter-connectivity since the Last Glacial Maximum (LGM). Identifying genetic connections between present-day chimpanzee communities and the role of past environmental change in shaping these 12 , 13 may be linked to behavioral variation in chimpanzee communities, 14 similar to what has been explored extensively in humans as a strongly migratory species. 15 Also, it will provide crucial tools for the development of conservation strategies for an endangered species that has suffered a dramatic decline in the last decades.…”

Soft sweeps predominate recent positive selection in bonobos (Pan paniscus) and chimpanzees (Pan troglodytes)

“…Chimpanzee populations living in more stable environments that were closer to Pleistocene refugia were recently described to exhibit less behavioral diversity than chimpanzees living in more seasonal habitats that are more distant to forest refugia (Kalan et al 2020). While the formation of these refugia may have resulted in periods of habitat stability for some bonobo and chimpanzee populations during glacial periods (Takemoto et al 2017; Barratt et al 2020), climatic fluctuations throughout the Pleistocene likely affected both the physical environment—via changes in habitat structure and type—and the social environment—via changes in the frequency of dispersal and intergroup encounters. Further, evidence of admixture within extant and between extant and extinct members of the Pan genus adds even more variation to the social environments in which these apes evolved (Hey 2010; Wegmann and Excoffier 2010; de Manuel et al 2016; Kuhlwilm et al 2019).…”