Ecological Plasticity Explains the Distribution of Sympatric and Allopatric Mouse Lemurs (Microcebus spp.) in Northeastern Madagascar

Abstract

Species distributions are shaped by complex biotic and abiotic interactions, which are often not fully understood. We investigated the ecological basis of co-occurrence and distribution of four partially sympatric and allopatric cryptic mouse lemur species (Microcebus spp.) in the Ambatosoa and Analanjirofo region of northeastern Madagascar. Using structural habitat characteristics, adaptability to habitat degradation, bioclimatic niches, and morphology (incl. body mass variability), we estimated n-dimensional hypervolumes of niche sizes and overlaps. 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%) that result from shifting cultivation practice. M. lehilahytsara exhibited the largest niche and range size, followed by M. jonahi and M. simmonsi. M. jonahi and M. simmonsi displayed significant fat deposition before the austral winter, indicating heterothermy as an adaptation to unpredictable environmental conditions. These two species were only found in allopatry, likely due to competition for critical resources like sleeping sites. The smaller M. lehilahytsara co-occurred 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 and M. simmonsi to persist in lowland habitats during cold phases of the Pleistocene but that it did not promote co-occurrence. In contrast, M. lehilahytsara may have lost lowland distributions due to a lower capacity to deposit fat. Our findings require further testing but provide a plausible explanation for a complex distributional pattern of sympatric and allopatric occurrences in northeastern Madagascar.