While species distribution models have been developed for semi-aquatic species, few have directly incorporated the hydrologic variables on which these species depend. The common hippopotamus (Hippopotamus amphibius) is a keystone species in African ecosystems. A semi-aquatic mammal whose skin characteristics result in extremely high evaporative losses, it is physiologically dependent on immersion for thermoregulation. We ask, does including hydrologic data improve models of species distribution for H. amphibius? Using both low-resolution, range-wide occurrence data and high-resolution, regional occurrence data, we develop species distribution models for H. amphibius with and without hydrologic variables, and compare their performance. We then predict future habitat suitability of H. amphibius in the context of climate change and hydrologic change, including water diversion for irrigation.
We found that including hydrologic data substantially improves the performance of species distribution models for H. amphibius, especially when using high-resolution occurrence data to develop the model. Our model predictions identified numerous locations across Africa as suitable habitat for H. amphibius that fell far outside of the commonly-used IUCN range map for the species, where presence of H. amphibius was confirmed by alternate sources of biogeographic data. We developed a more accurate present-day range map of H. amphibius, as well as projections of the future distribution of H. amphibius given several scenarios of anthropogenic climate and hydrologic change. Our findings imply that hydrologic data can successfully be used to improve species distribution models for semi-aquatic species.