Ecological plasticity explains the distribution of sympatric and allopatric mouse lemurs (Microcebus spp.) in northeastern Madagascar
Species distributions are shaped by complex biotic and abiotic interactions. We studied major ecological drivers of the distribution of four cryptic mouse lemur species (Microcebus spp.) in northeastern Madagascar, across sympatric and allopatric ranges. Using structural habitat characteristics, adaptability to habitat degradation, bioclimatic niches, and morphology, we estimated n-dimensional hypervolumes of niche sizes and overlaps. Annual body mass variability was analyzed as an indicator of heterothermy, a potential indicator for ecological plasticity. M. jonahi and M. simmonsi were found almost equally often in forest- and fallow-derived habitats (52% and 58%, respectively), while M. lehilahytsara predominantly occupied fallow habitats (71%), likely driven by the coexistence with other species. M. lehilahytsara exhibited the largest niche and range size, followed by M. jonahi and M. simmonsi. In contrast, M. macarthurii was restricted to a narrow niche and range. M. jonahi and M. simmonsi displayed significant fat deposition before the austral winter, indicating heterothermy as an adaptation to unpredictable environmental conditions. These species were only found in allopatry, likely due to competition for critical resources like sleeping sites. The smaller M. lehilahytsara coexisted with M. jonahi and M. macarthurii potentially by adjusting its niche to avoid competition with these larger-bodied species. We hypothesize that heterothermy allowed M. jonahi, M. simmonsi, and M. macarthurii to persist in lowlands during Pleistocene climatic challenges but that it did not promote coexistence. In contrast, M. lehilahytsara may have lost lowland distributions due to a lower ability to store fat. Our findings require further testing but provide a plausible explanation for a complex distributional pattern of sympatric and allopatric occurrences.