個體、族群與物種層次棲位變異研究:以小型哺乳動物群聚為例

Niche variation at population and community levels mediates niche partitioning, and can play a role maintaining species coexistence. Ecological opportunity (resource diversity) and competition are two of the main mechanisms underlying population niche expansion, among-individual variation within the population niche, and niche overlap between species. In this study we used data accumulated over the past years, including stable carbon and nitrogen isotope data of 635 individual rodents from 4 species across 9 sites in the montane region of Taiwan, to test the effects of ecological opportunity and competition on population niche size, inter-individual difference within the population niche, and inter-specific niche overlap. We used mark-recapture data to confirm that the rodents experienced stronger intra- than inter-specific competition by showing a negative response of population change rate to conspecific abundance. We quantified population niche size by the Bayesian Standard Ellipse Area, based on which niche overlap was estimated. We quantified inter-individual difference by isotopic divergence, isotopic evenness and isotopic uniqueness. The results showed that population niche size increased with ecological opportunity (increased resource diversity represented by larger basal resource isotopic variation), but was not influenced by intra- or inter-specific competition (represented by conspecific or heterospecific abundance respectively). On the other hand, the inter-individual difference (isotopic evenness) increased with intra-specific competition but not inter-specific competition or ecological opportunity. At community level, pairwise niche overlap between species of different trophic roles (herbivore—omnivore pair) increased with competition (the combined abundance of the pair) but not ecological opportunity. Taken together, this study demonstrated that ecological opportunity and competition influenced different aspects of niche variation in these rodents, and the trophic role of the species also played a role. We suggest that niche packing in these rodent communities might be achieved through increased niche overlap rather than increased niche partitioning, as competition drives individuals to differentiate from their conspecifics at the cost of overlapping more with the heterospecifics.