Niche overlap in rodents increases with competition but not ecological opportunity: A role of inter‐individual difference

Abstract

Niche variation at population level mediates niche packing (i.e. patterns of species' spread within the niche space) and species coexistence at community level. Competition and ecological opportunity (resource diversity) are two of the main mechanisms underlying niche variation. Dense niche packing could occur through increased niche partitioning or increased niche overlap. In this study, we used stable carbon and nitrogen isotope data of 635 individual rodents from four species across nine sites in the montane region of a subtropical island to test the effects of competition and ecological opportunity on population isotope niche size, inter‐individual niche difference within population and interspecific niche overlap within community. We used the Bayesian Standard Ellipse Area (SEAB, the ellipse area enclosed by carbon and nitrogen isotope values of organisms on a bi‐plot) to estimate population niche size and interspecific niche overlap. Inter‐individual niche difference within population was quantified as isotopic divergence and isotopic uniqueness. We used rodent abundance (the number of unique individuals captured) to measure competition and plant isotope niche size (plant SEAB) to measure ecological opportunity. The rodents experienced competition as evidenced by a negative relationship between population change rate and conspecific abundance. Rodent population niche size increased with ecological opportunity but not competition. The inter‐individual niche difference (isotopic uniqueness) increased with competition (interspecific competition only) but not ecological opportunity. At community level, interspecific niche overlap (herbivore–omnivore pair only) increased with competition (the combined abundance of the pair) but not ecological opportunity. This study demonstrated that isotope niche variation of the rodents could be hierarchically influenced by ecological opportunity and competition, with the former setting the limit of population niche size across communities and the latter shaping inter‐individual niche difference and interspecific niche overlap within communities. Under strong intraspecific competition and limited ecological opportunity for niche expansion, individuals may choose to increase their isotopic uniqueness from conspecifics at the cost of overlapping with heterospecifics of different trophic roles within the community niche space as overall competition increases. Denser niche packing of these rodent communities might be achieved through increased niche overlap.

Increasing species richness along elevational gradients is associated with niche packing in bat assemblages

“…We suggest that this low niche overlap is an indication of niche partitioning in a potentially resource-deficient, harsh, high-elevation landscape. Similar examples are found in didelphid marsupials and rodents which show low isotopic niche overlap in less productive environments (Bubadué et al, 2021) or with increased heterospecific competition (Shaner & Ke, 2022).…”

Geographical distribution and species variation of gut microbiota in small rodents from the agro‐pastoral transition ecotone in northern China

“…Additionally, our results suggested that geographical factors play a species‐specific role in shaping the α‐diversity of host gut microbiota, with A. agrarius and C. barabensis populations being more susceptible to the influence of geographical factors, whereas this influence was less pronounced in R. norvegicus populations. We found that there was no significant difference in β‐diversity of gut microbiota between the A. agrarius and C. barabensis at site 3, indicating a higher similarity in gut microbiota between these two species in a homogenized environment, which could be disadvantageous as it may intensify inter‐specific competition between the two species (Anders et al., 2022 ; Shaner & Ke, 2022 ). In addition, the observed within‐group differences being higher than between‐group differences in certain cases (such as R. norvegicus ) suggests unique microbial adaptations within specific populations (He et al., 2020 ).…”

Reciprocated competition between two forest carnivores drives dietary specialization

“…In addition, we quantified ecological opportunity at each site by the area of the Bayesian isotopic standard ellipse of the available dietary items (e.g. Shaner & Ke, 2022).…”