Contrasting species- and trait-specific effects of deer wallows on life-history performance in two amphibians

Ecosystem engineers create or modify habitats and can thereby affect the populations of associated species. Although these effects have often been evaluated using abundance-based measures, the survival and growth of individuals within engineered habitats offer a different perspective on the potential significance of these habitats for populations. Yet such fitness-related performance has rarely been compared directly between engineered and non-engineered habitats. Here, we compared the larval survival and growth of two amphibian species ( Rana pirica and Hynobius retardatus ) utilizing wallows created by sika deer ( Cervus nippon yesoensis ) with their performance in natural ponds. Our survey revealed that R. pirica survived better in wallows than in ponds (mean larval survival: 28.6% vs. 9.9%), whereas H. retardatus survived better in ponds than in wallows (30.4% vs. 8.5%). Additionally, in wallows, R. pirica reached metamorphosis at a smaller body size (13.0 vs. 14.9 mm) and took longer to metamorphose (86.8 vs. 76.3 days). These results show that engineered habitats do not have uniformly positive or negative effects on associated species: their effects can differ between species and between life-history components. Our study demonstrates that evaluating multiple aspects of individual performance can reveal contrasting effects of engineered habitats that would be overlooked when relying on a single response.