Data from: Is dietary or microhabitat specialization associated with environmental heterogeneity in horned lizards (Phrynosoma)?

Niche breadth is predicted to correlate with environmental heterogeneity, such that generalists will evolve in heterogeneous environments and specialists will evolve in environments that vary less over space and time. We tested the hypothesis that lizards in a heterogeneous environment were generalists compared to lizards in a homogeneous environment. We compared niche breadths of greater short-horned lizards by quantifying resource selection in terms of two different niche axes, diet (prey items and trophic level) and microhabitat (ground cover and shade cover), between two populations occurring at different elevations. We assessed the heterogeneity of dietary and microhabitat resources within each population’s environment by quantifying the availability of prey items, ground cover, and shade cover in each environment. Overall, our results demonstrate that despite differences in resource heterogeneity between elevations, resource selection did not consistently differ between populations. Moreover, environmental heterogeneity was not associated with generalization of resource use. The low-elevation site had a broader range of available prey items, yet lizards at the high-elevation site demonstrated more generalization in diet. In contrast, the high-elevation site had a broader range of available microhabitats, but the lizard populations at both sites were similarly generalized for shade cover selection, and were similarly specialized for ground cover selection. Our results demonstrate that environmental heterogeneity of a particular resource does not necessarily predict the degree to which organisms specialize on that resource.

生态位宽度（niche breadth）被预测与环境异质性（environmental heterogeneity）相关：即在异质环境中会演化出泛化种（generalists），而在时空变化较小的环境中则会演化出特化种（specialists）。我们针对“异质环境中的蜥蜴相较于同质环境（homogeneous environment）中的蜥蜴为泛化种”这一假说开展了检验。我们针对两个不同海拔（elevations）分布的大短角蜥（greater short-horned lizards）种群，通过两个不同生态位轴（niche axes）量化资源选择（resource selection）情况，以此比较二者的生态位宽度：这两个维度分别为食物（猎物种类与营养级（trophic level））以及微生境（microhabitat，包括地表覆盖（ground cover）与遮阴覆盖（shade cover））。我们通过量化各环境中猎物种类、地表覆盖与遮阴覆盖的可获得性，评估了每个种群所在环境的食物与微生境资源异质性。总体而言，本研究结果表明：尽管不同海拔间的资源异质性存在差异，但种群间的资源选择并未呈现出一致性差异；此外，环境异质性与资源利用的泛化程度并无关联。低海拔样地（low-elevation site）的可获得猎物种类范围更广，但高海拔样地（high-elevation site）的蜥蜴在食物选择上呈现出更强的泛化性。与之相反，高海拔样地的可获得微生境范围更广，但两个样地的蜥蜴在遮阴覆盖选择上均表现出相近的泛化程度，且在地表覆盖选择上均表现出相近的特化程度。本研究结果证实：某一类资源的环境异质性，未必能预测生物体对该资源的特化程度。