Habitat and not topographic heterogeneity constrains the range sizes of African mammals

Aim: The extinction risks of species are influenced by their geographical range sizes, as species with smaller ranges are more likely to go extinct following disturbance events. Theoretically, heterogeneous landscapes can maintain small-ranged species, because they facilitate the coexistence of taxa that are each constrained to distinct abiotic conditions. However, we do not fully understand whether this process is more attributable to variation in habitat types (habitat heterogeneity) or physical elevations (topographic heterogeneity) across landscapes. Here, we compare the influences of habitat versus topographic heterogeneity on mammalian range sizes in Africa.

Location: Africa.

Taxon: Mammalia.

Methods: We built a phylogenetic generalized least squares model to predict the range sizes of 1033 mammalian species from their functional traits and abiotic conditions. We assessed how the performance of the model changed when we incorporated measures of the local habitat and, separately, topographic heterogeneity that species experience.

Results: Habitat and topographic heterogeneity are weakly correlated across Africa (ρ = 0.14). Habitat heterogeneity is inversely related to range size (model coefficient = −0.88). Incorporating habitat heterogeneity significantly decreased the model's AICc, increased its likelihood and increased the proportion of variance that is explained in the range sizes of species. Conversely, topographic heterogeneity is not significantly related to range size and had no impact on the model's AICc, likelihood or predictive performance. This contrast between habitat and topographic heterogeneity is particularly prevalent in carnivorous mammalian clades. Results at multiple spatial resolutions differed minimally.

Main Conclusions: Our findings advance ecological theory by demonstrating that a landscape's variation in habitats, and not in elevations, relates inversely with mammalian range size and therefore facilitates the coexistence of small-ranged mammals. Conservation efforts in regions of high habitat heterogeneity will be critical to prevent extinctions in Africa's biodiverse mammalian species.