Resistance and Resilience of Alpine Lake Fauna to Fish Introductions

Abstract

This paper reports on the response by amphibians, benthic macroinvertebrates, and zooplankton in naturally fishless alpine lakes to fish introductions and subsequent fish disappearance. We assessed resistance (the degree to which a system is altered when the environment changes) by comparing faunal distribution and abundance in lakes that have never been stocked with fish vs. the distribution and abundance in lakes that have been stocked and still contain fish. We assessed resilience (the degree and rate of a system's return to its previous configuration once the perturbation is removed) by comparing faunal distribution and abundance in lakes that were stocked at one time but have since reverted to a fishless condition (stocked-now-fishless lakes) vs. the distribution and abundance in lakes that have never been stocked. We quantified recovery rates and trajectories by comparing faunal assemblages of stocked-now-fishless lakes that had been fishless for 5-10, 11-20, and Ͼ20 yr.Faunal assemblages in the study lakes had low resistance to fish introductions, but in general showed high resilience. The mountain yellow-legged frog (Rana muscosa), conspicuous benthic macroinvertebrates, and large crustacean zooplankton (Ͼ1 mm) were dramatically reduced in distribution and abundance by fish introductions but generally recovered to predisturbance levels after fish disappearance. Inconspicuous benthic invertebrate taxa, small crustacean zooplankton (Ͻ1 mm), and rotiferan zooplankton (Ͻ0.2 mm) were either unaffected by fish or increased in the presence of fish. For both the benthic macroinvertebrate community and the zooplankton community as a whole, fish disappearance was followed by a steady change away from the configuration characteristic of fishcontaining lakes and toward that of lakes that had never been stocked. Both communities remained markedly different from those in never-stocked lakes 5-10 yr after fish disappearance and converged on the configuration of never-stocked lakes only 11-20 yr after fish disappearance.Recovery was likely facilitated by the winged adult stages of many benthic macroinvertebrates, resting eggs of zooplankton, and nearby source populations of frogs. However, many frog populations have disappeared since the time that lakes in this study reverted to a fishless condition, and the viability of zooplankton egg banks should decline in fishcontaining lakes over time. As a result, faunal resilience may be lower in lakes that revert to a fishless condition today than is suggested by the results of our study. These findings have important implications for the restoration of alpine lake ecosystems.

The importance of phenotypic diversity in conservation: Resilience of palmate newt morphotypes after fish removal in Larzac ponds (France)

“…In contrast to another model system (Knapp et al 2001), we did not find a significant effect of neighbouring populations on the abundances of metamorphs and paedomorphs in ponds where fish disappeared. Larzac ponds inhabited by facultatively paedomorphic newts are not so distant from extirpation ponds, making recolonization possible.…”

“…In four cases, this was done through local actions (temporary drying of the ponds and fish removal) whereas in the others, fish did not sustain and disappeared by themselves, possibly because of unsuitable aquatic conditions. A period of around 10 years between fish extirpation and the observed resilience of metamorphs and metamorphs during our survey is in agreement with the results from other authors on the timing of resilience of organisms such as amphibians (Knapp et al 2001). The shortest recovery time for paedomorphic palmate newt found in this study was four years, but we cannot reject potential faster rates.…”

“…We then used these distribution data to determine the potential effect of the distance to the closest pond inhabited by palmate newts on the abundances of paedomorphic and metamorphic newts found after fish removal in the present study. Indeed, previous authors found that the proximity of nearby source populations could influence the probability of resilience of organisms (Knapp et al 2001). …”

“…Aquatic ecosystems have been shown to recover after only a certain number of years subsequently to threat removal (Knapp et al 2001). However, amphibians could rapidly recover, reaching the same population sizes as in control lakes in only a few years (Funk and Dunlap 1999;Vredenburg 2004;Knapp et al 2007;Pope 2008).…”

“…Despite their low resistance to environmental disturbance such as fish introductions, amphibians can also show a high degree of resilience, i.e., the ability to return to their previous configuration once the perturbation is removed (Knapp et al 2001). For instance, the removal of fish from lakes allowed the restoration of frog and salamander populations (Vredenburg 2004;Knapp et al 2007;Pope 2008).…”