Assessing niche evolution and population connectivity over glacial cycles for two Malagasy small mammals

Background/Question/Methods

We use ecological niche models (ENMs) to test for niche evolution and assess past and present population connectivity of two Malagasy small mammals, Eliurus majori and Oryzorictes hova.  Phylogeographic studies have identified two lineages within each of these tropical montane species.  Pleistocene climatic oscillations may have affected population connectivity, with allopatric isolation likely during the warmer interglacials.  For each species, we first use ENMs to test for niche conservatism between lineages.  We then model each species' niche and predict the suitable areas in the present and at the Last Glacial Maximum (LGM; 21 KYA), proxies for past interglacial and glacial maxima, respectively.  We calibrated models using occurrence records, 19 bioclimatic variables, and Maxent.  To make high-quality models, we reduced the effects of sampling biases (via spatial filtering), implemented principles of study-region selection, and tuned model settings (to approximate optimal complexity).  

Results/Conclusions

Tests of interpredictivity between lineages showed moderate (O. hova) to high (E. majori) levels of niche conservatism.  Present-day predictions for E. majori indicated several disjunct areas of suitable conditions, whereas projections to the LGM suggested more extensive areas and higher connectivity.  Results for O. hova were similar, but with larger areas of suitable conditions during both time periods.  Overall, the results match the prediction of range contraction during interglacials and expansion at glacial maxima.