Abstract
In species with complex life cycles, stage-specific effects of environmental conditions combine with factors regulating stage-specific recruitment to determine population-level response to habitat disturbance. The abundance of the stream salamander Gyrinophilus porphyriticus (Plethodontidae) is negatively related to both logging-associated sedimentation and brook trout (Salvelinus fontinalis) in headwater streams throughout New Hampshire, USA. To understand the mechanisms underlying these patterns, we investigated stage-specific and interactive effects of sedimentation and brook trout on G. porphyriticus. We conducted quantitative surveys of salamanders, brook trout, and substrate embeddedness in 15 first-order streams and used a controlled experiment to test the direct and interactive effects of these factors on larval growth and survival. G. porphyriticus larvae and adults had opposite patterns of response to sediment and brook trout. Multiple regression analysis of our survey data indicated that abundance of larvae was negatively related to brook trout abundance, but unrelated to substrate embeddedness. In contrast, abundance of adults was primarily related to substrate embeddedness. Consistent with the field pattern of larval abundance, brook trout had a negative effect on growth and survival of larvae in the experiment. However, there was no effect of sediment and no interaction between brook trout and sediment. Larval and adult abundances were not significantly correlated in the study streams, indicative of the independent effects of sedimentation and brook trout on G. porphyriticus populations. These results suggest that adult resistance to fish may facilitate G. porphyriticus coexistence with brook trout, and that larval resistance to sedimentation can buffer populations from extinction in fishless streams impacted by logging. In streams with brook trout, where larval abundances are low, reductions in adult abundance caused by logging impacts may pose a risk to species persistence. Our findings underscore the value of information on species life history, demography, and community ecology in assessing sensitivity to anthropogenic perturbation.
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