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Resistance and resilience of alpine lake fauna to fish introductions.
Knapp, Roland1, Matthews*, Kathleen2, Sarnelle, Orlando3, 1 2 3
ABSTRACT- The ability of ecosystems to recover following perturbations is fundamental to the growing field of restoration ecology, but remains poorly understood. Our study quantified the response by amphibians, benthic macroinvertebrates, and zooplankton in naturally fishless alpine lakes to fish introductions and subsequent fish disappearance. We assessed assemblage resistance and resilience by comparing faunal distribution and abundance among lakes with different fish stocking histories (never-stocked, stocked-fish-present, stocked-now-fishless; n = 190-533 lakes). We quantified recovery rates and trajectories by comparing faunal assemblages of stocked-now-fishless lakes that had been fishless for 5-20+ years. Amphibians, conspicuous benthic macroinvertebrates, and large zooplankton had low resistance and were dramatically reduced by fish introductions, but showed high resilience and eventually recovered to pre-disturbance levels after fish disappearance. Multivariate analyses showed that fish disappearance was followed by a steady change away from the configuration characteristic of fish-containing lakes and toward that of lakes that had never been stocked. Faunal assemblages in stocked-now-fishless lakes remained markedly different from those in never-stocked lakes 5-10 years after fish disappearance, but converged on the configuration of never-stocked lakes 11-20 years after fish disappearance. Resilience may be lower in lakes that revert to a fishless condition today than in our study because many frog populations have disappeared and the viability of zooplankton egg banks should decline in fish-containing lakes over time. These findings have important implications for the restoration of alpine lake ecosystems.
KEY WORDS: resistance, resilience, alpine lakes, nonnative fish