Long-term population dynamics of small mammals in tropical dry forests, effects of unusual climate events, and implications for management and conservation

Understanding the consequences of biotic and abiotic variability on population dynamics is fundamental to assessing anthropogenic impacts, such as global climate disruption, on populations and species. Our understanding from studies to date is poor, although some long-term studies of small mammals in temperate ecosystems have elucidated the roles of climate and of interspecific interactions in their population dynamics. However, the lack of long-term studies in the tropics is a major impediment to understanding species and ecosystems in these regions. We analyzed the long-term population dynamics of seven species of small mammals from two adjacent tropical dry forests with contrasting phenology in a protected area of western Mexico. We modeled these dynamics using data from an 18-year live-trapping database, and we evaluated the effects of intra- and interspecific interactions, primary productivity, temperature, precipitation, and unusual climate events. Intraspecific interactions were the most common factors in every population, while interspecific interactions had only a mild positive interaction between few species. While we found that the effect of temperature was not relevant to population dynamics, precipitation caused positive effects on all species, either by directly enhancing the reproductive rate or, indirectly, by triggering changes in primary productivity. Extreme climate events created intense signals. Oryzomys melanotis, an invasive and opportunistic species, benefited from these events, and two populations were harmed by them: Peromyscus perfulvus and Liomys pictus, the small mammal with the most abundant population of the upland forest, which was extirpated for over 16 months. Our results suggest that sharp reductions in precipitation and more frequent extreme climate events-both predicted by global climate disruption regional models-would have dramatic effects, adding to the other anthropogenic pressures these forests are already suffering (habitat loss, excessive management). These results emphasize the importance of protected and unmanaged refugia, such as our study site, to provide sources for refaunation following local extinctions.