Modeling the ecological niche of the Nigeria-Cameroon Chimpanzee under climate change

Ecological niche theory states that a set of environmental conditions exists that a species relies upon in order to survive and reproduce. Collectively, these variables define a species' niche, which includes a species' dispersal abilities and its range. Ecological niche modeling predicts the distributions of species by using information from environmental variables across geographic space, making it a valuable tool for studying how environment affects population dynamics. With accurate species presence data and geospatial information that describe its known habitat, ENMs can effectively map a species' realized niche across geographical space, and for closely related taxa, be used to understand the ways that ecological variation might contribute to speciation. These modeled ecological niches can also be projected onto other areas to test for habitat suitability as well as over a time series of predicted climate change, to see how the realized niche may change in the future.;The Nigeria-Cameroon Chimpanzee (Pan troglodytes ellioti) is found in the Gulf of Guinea biodiversity hotspot located in western equatorial Africa. This subspecies is threatened by habitat fragmentation due to logging and agricultural development, hunting for the bushmeat trade, and possibly by climate change. Although P. t. ellioti appears to be geographically separated from the neighboring central chimpanzee (P. t. troglodytes ) by the Sanaga River, recent population genetics studies of chimpanzees from across this region suggest that additional factors might also be important in their separation. The main aims of this study were: 1) to model the distribution of suitable habitat for P. t. ellioti across Cameroon and Nigeria and P. t. troglodytes in southern Cameroon, 2) to determine which environmental factors best predict their optimal habitats, and 3) to compare modeled niches and test for their levels of divergence from one another. A final aim of this study was to examine the ways that climate change might impact suitable chimpanzee habitat across the region under various scenarios.;Ecological niche models (ENMs) were created using the software package Maxent for the three populations of chimpanzees that have been inferred to exist in Cameroon and eastern Nigeria: (i) P. t. troglodytes in southern Cameroon, (ii) P. t. ellioti in northwestern Cameroon, and (iii) P. t. ellioti in central Cameroon. ENMs for each population were compared pairwise using the niche comparison test in ENMtools, which revealed complete niche divergence with very little geographic overlap of suitable habitat between populations. These findings suggest that a positive relationship may exist between environmental variation and the partitioning of genetic variation found in chimpanzees across this region. Finally, ENMs for each population were projected under three different climate change scenarios for years 2020, 2050, and 2080. Suitable habitat of P. t. ellioti in Northwest Cameroon / Eastern Nigeria is expected to remain largely unchanged through 2080 in all considered scenarios. In contrast, P. t. ellioti in central Cameroon, which represents half of the population of this subspecies, is expected to experience drastic reductions in its ecotone habitat over the coming century.