Estimating glacial refugia for chimpanzees over the last 120,000 years

We just published a new paper that provides insights into where chimpanzees avoided climate instability during glacial and interglacial periods in Africa over the past 120,000 years. Understanding past responses to change is essential for the future conservation of species because it helps to increase our understanding of how climate change impacts biodiversity, and how we may need to mitigate against predicted biodiversity loss in the future.

Fig. 1. Demonstration of the changing modelled habitat suitability over time for chimpanzees. Subspecies ranges are marked by green lines, and Maley’s (1996) refugia are marked as dashed black lines. Fig available on Figshare here.

To conduct this research we used chimpanzee presence data from the IUCN/SSC APES database combined with paleoclimatic reconstructions and historical human density data to model chimpanzee habitat suitability since the Last Interglacial period (120,000 years ago, see Fig. 1). We built species distribution models for 62 different snapshots of time during this time period, using these to quantitatively assess which areas have remained more stable for chimpanzees, and which have been subject to high levels of change. Our overarching results using three different estimates of habitat stability (Fig. 2D-F) show that several areas previously considered as refugia from global change (Maley, 1996) may be much larger than previously thought for chimpanzees (Fig. 2A). We demonstrate that that these areas closely match the species richness patterns of important keystone food resources for primates (figs and palms, Fig. 2B-C), together suggesting that these additional refugial areas may deserve additional conservation protection. Our work here provides a new resource to aid our understanding of the rich behavioural and genetic diversity patterns exhibited by chimpanzees, and how past global change may have influenced this. It may also help guide predictions of future global change and how it will affect biodiversity.

Fig. 2. Stability of chimpanzee habitat suitability over 62 snapshots of paleoclimate reconstructions representing the past 120,000 years. (A) Our refugia (in blue) are defined as all pixels with a dynamic stability value > 0.97 in habitat suitability maps over the 120,000 year time period, compared with refugia defined by Maley (1996) (in gray). (B) Fig species richness based on data from Kissling et al. (2007). (C) Palm species richness based on data from Blach-Overgaard et al. (2013). (D) Refugia inferred by the dynamic stability approach. (E) Refugia inferred by the static stability approach. (F) Refugia inferred by the CV stability approach. In maps (B) and (C), more yellow colors represent higher species richness (previous estimates of forest refugia (Maley, 1996) drawn in red, and green, respectively. In maps (D-F), warmer colors represent areas of higher suitability over time that have remained stable compared with previous estimates of forest refugia (dotted black lines, Maley, 1996). Country borders (gray lines) and chimpanzee subspecies ranges (green lines, Humle et al., 2016) are also shown

You can find press releases about this work here and here, and the publication is available open access here.

We also provide a DRYAD data and script package so that these analyses can be re-run, or applied to other species/geographic regions.

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