Species in transformed habitats, frequently labeled as environmental generalists, tend to show broader niches than species in natural habitats. However, how population niche expansion translates into changes in the niches of individual organisms remains unclear, particularly in the context of habitat transformation. Niche expansion could be a product of individuals having broader niches, greater distances among individuals’ niches, or a combination of both processes. This would challenge the traditional conceptions on niche dynamics, which emphasize the role played by individual specialization (IS). Here, using stable isotopes, we computed total niche width (TNW), its within- and between-individual components (WIC and BIC), and IS (the ratio WIC/TNW), in 13 populations of 6 bird species and 8 populations of 3 frog species in natural and transformed habitats. We confirmed that species had broader niche width in transformed than in natural habitats, yet population niche expansion across habitats was mainly a product of increased distance between individuals. Within each habitat type, increases in TNW were linked to increases in WIC for all habitat types, while relationships between TNW and BIC were found in transformed but not in natural habitats. Hence, both increased individual niche width and increased distance among individuals were apparent within habitats, particularly in transformed ones, where increases in WIC dominated. Neither across or within habitats was niche expansion associated with increasing IS. Therefore, our results overturn traditional conceptions associated with the niche variation hypothesis and illustrate that niche expansion is not invariably associated with increased IS, because the distance between individual’s niches (BIC) can increase, as well as the breadth of those niches (WIC).

中文翻译：

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如何成为通才物种？栖息地转换梯度的个体生态位变异

转化栖息地中的物种，通常被称为环境通才，往往比自然栖息地中的物种表现出更广泛的生态位。然而，种群生态位扩张如何转化为个体生物生态位的变化仍不清楚，特别是在栖息地转变的背景下。利基扩张可能是个体拥有更广泛利基、个体利基之间距离更大的产物，或者这两种过程的组合。这将挑战传统的利基动态概念，这些概念强调个人专业化 (IS) 所发挥的作用。在这里，使用稳定同位素，我们计算了总生态位宽度 (TNW)、其个体内部和个体之间的成分（WIC 和 BIC）和 IS（WIC/TNW 的比率），在自然和转化栖息地的 6 种鸟类的 13 个种群和 3 种青蛙的 8 个种群中。我们证实物种在转化的生态位宽度比自然栖息地更宽，但跨越栖息地的种群生态位扩张主要是个体之间距离增加的产物。在每种栖息地类型中，TNW 的增加与所有栖息地类型的 WIC 增加有关，而 TNW 和 BIC 之间的关系在转化的栖息地中发现，但在自然栖息地中没有。因此，在栖息地中，个体生态位宽度的增加和个体间距离的增加都很明显，特别是在转化的栖息地中，WIC 的增加占主导地位。无论是跨栖息地还是栖息地内，生态位扩张都与增加 IS 相关。所以，