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

• Published in: Ecology and evolution 2019-05, Vol.9 (10), p.5542-5550
• Main Authors: Refsnider, Jeanine M., Carter, Sarah E., Kramer, Gunnar R., Siefker, Adam D., Streby, Henry M.
• Format: Article
• Language: English
• Subjects: Abajo Mountains; Animal behavior; Animal reproduction; Diet; Elevation; Environment; Environmental conditions; Ground cover; Habitats; Heterogeneity; horned lizard; Hypotheses; Lizards; Microenvironments; Microhabitats; Morphology; Niche breadth; Niches; Organisms; Original Research; Phrynosoma hernandesi; Population; Populations; Prey; Shade; shade cover; Specialization; trophic level; Trophic levels
• ISSN: 2045-7758; 2045-7758
• DOI: 10.1002/ece3.5109

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. Niche theory predicts that variable environments should support resource generalists. We tested this prediction along two different resource axes, diet and microhabitat, in two lizard populations. Despite differences in resource heterogeneity between environments, resource selection did not consistently differ between populations; therefore, environmental heterogeneity of a particular resource does not necessarily predict degree of specialization for that resource.