Niche overlap in rodents increases with competition but not ecological opportunity: A role of inter‐individual difference. Issue 8 (7th June 2022)

• Record Type: Journal Article
• Authors: Shaner, Pei‐Jen L.; Ke, Ling‐hua
• Is Part Of: Journal of animal ecology. Volume 91:Issue 8(2022)
• Page Start: 1679
• Page End: 1692
• Publication Date: 2022-06-07
• Subjects: competition -- ecological opportunity -- inter‐individual niche difference -- niche overlap -- niche partitioning -- niche variation -- rodents -- stable isotope; Animal ecology -- Periodicals; 591.7
• DOI: 10.1111/1365-2656.13750
• Languages: English
• ISSNs: 0021-8790

Abstract

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. Abstract : This study showed that ecological opportunity (resource diversity) constrains rodent isotope niche expansion, while competition shapes how individuals arrange themselves within the population niche space (inter‐individual niche difference) and species within the community niche space (interspecific niche overlap). 摘要: 族群層級之生態棲位變異可調節群聚層級之生態棲位堆疊(亦即物種在生態棲位空間中的分佈樣態)以及物種共存。競爭與生態機會(資源豐度)是影響生態棲位變異的兩個重要機制。生態棲位區隔或生態棲位重疊增加，都有可能導致密集的生態棲位堆疊。 本研究利用亞熱帶島嶼山區9個地點的4個齧齒目物種共635隻個體之穩定碳、氮同位素資料，探討競爭與生態機會對族群生態棲位大小、族群內個體間生態棲位差異以及群聚內物種間生態棲位重疊的影響。 我們使用貝式標準橢圓形面積(縮寫為SEAB，亦即在碳、氮同位素兩軸上包括大部分個體之橢圓形面積)估算族群生態棲位面積以及物種間生態棲位重疊度。個體間生態棲位差異則是以同位素分歧度與同位素獨特性進行量化。我們使用各物種的族群數量(亦即每地點捕捉到的個體數)量化競爭，並使用植物同位素棲位面積(植物SEAB)量化生態機會。 各物種皆受到種內競爭影響，隨著族群數量越高，族群變化率越低。族群生態棲位面積隨生態機會增加而變大，但不受競爭的影響。個體間生態棲位差異(同位素獨特性)隨競爭(種間)增加而增加，但不受生態機會的影響。在群聚層級上，種間生態棲位重疊度(植食性與雜食性物種間)隨競爭(成對兩物種之總族群數量)增加而增加，但不受生態機會的影響。 本研究顯示齧齒目動物生態棲位變異可能同時受到生態機會與競爭的影響，在跨群聚的較大尺度上，前者限制族群生態棲位的大小，在群聚內的較小尺度上，後者影響個體間生態棲位差異與物種間生態棲位重疊。在種內競爭激烈且生態機會有限的情況下，隨著群聚內整體競爭(包含種內與種間)壓力增加，個體可能會選擇增加同位素獨特性，即便他們需付出與不同食性之異種生態棲位重疊度增加的代價。因此，這些齧齒目動物群聚可能是透過增加生態棲位重疊度達到更密集的生態棲位堆疊。