Niche variation can help explain the patterns and processes of resource use that contribute to population differentiation and species coexistence. Using stable carbon-nitrogen isotope values as proxies for trophic niche, I explored the role of niche width and niche shift in shaping interspecific niche partitioning in small mammal communities, as well as intraspecific niche differentiation across multiple communities, in Taiwan's montane region. I hypothesize that the omnivorous species would shape the amount of niche overlap among coexisting species and exhibit a higher degree of population differentiation than herbivores and insectivores. An observational study was carried out between 2015 and 2018 across eight sites (i.e. eight small mammal communities). Each site was dominated by two to four small mammal species. The animals were live-captured and their hair tissues taken for isotope analyses. Trophic niche width was quantified with standardized ellipse area, which provided the basis for calculating the amount of niche overlap (i.e. ellipse areas overlapped by a pair of species). Niche shift was quantified with the averaged Euclidean distance between niche centers of pairs of populations across communities, which also reflected the degree of intraspecific niche differentiation.
Results/Conclusions
Contrary to my predictions, the two dominant omnivorous species, Apodemus semotus and Niviventer culturatus, showed narrow and conserved trophic niche compared to herbivorous Eothenomys melanogaster. It is the variation in niche width and niche shift of E. melanogaster that shaped the degree of niche overlap among coexisting species. These findings suggest that: 1) omnivory in small mammals might be a fine-tuned trophic niche with low variability; 2) trophic niche of some presumed herbivorous species, such as E. melanogaster, might require a more comprehensive review across their geographic range; and 3) trophic group affiliation might not relate well to a species' position along the gradient of niche specialization-generalization.