Higher temperatures enhance the effects of invasive sportfish on mountain zooplankton communities

Abstract

Summary 1. Decades of introductions of exotic sportfish to mountain lakes around the world have impoverished them biologically, and this may be exacerbated by global warming. We assessed the current status of invasive salmonids and native zooplankton communities in 34 naturally fishless lakes along an elevational gradient, which served as an environmental proxy for the expected effects of climate change. 2. Our main goal was to explore how climate‐related variables influence the effects of stocked salmonids on the total biomass, species richness and taxonomic composition of zooplankton. We predicted that warmer conditions would dampen the negative predatory effects of exotic brook trout (Salvelinus fontinalis) on zooplankton communities because more temperate lakes contain a greater diversity of potentially tolerant species. 3. Instead, we discovered that the persistence of stocked brook trout in the warmer lakes significantly amplified total zooplankton biomass and species richness. In colder and deeper lakes, zooplankton were relatively unaffected by S. fontinalis, which however persisted better in alpine lakes than at lower elevations after stocking practices were halted over two decades ago. Warmer lake conditions and higher concentrations of dissolved organic carbon (DOC) were significant primary drivers of zooplankton species turnover, both favouring greater species diversity. 4. Our findings of an ecological surprise involving potential synergistic positive effects of climate warming and exotic trout on native zooplankton communities presents a conundrum for managers of certain national mountain parks. Present mandates to eradicate non‐native trout and return the mountain lakes to their naturally fishless state may conflict with efforts to conserve biodiversity under a rapidly changing climate.

Climate constrains lake community and ecosystem responses to introduced predators

“…Similar zooplankton species were found in lakes with fish at all elevations, consistent with previous findings that both fish and higher temperatures independently select for a similar set of species [32]. In past studies, the mechanism invoked to explain this pattern is that high temperature and fish both select for small-bodied species.…”

Linking zooplankton richness with energy input and insularity along altitudinal and latitudinal gradients

“…A significant proportion of variation in zooplankton species richness remained unexplained by our original hypotheses. Therefore, we also conducted a post hoc analysis to evaluate for potential effects of pH and the presence of fish (e.g., Messner et al ; MacLennan et al in press). In this analysis, we compared the evidence supporting the best model from our initial analysis (i.e., the “energy and geography” model) to more complex models including the energy and geography variables as well as lake pH, the presence of fish, or both.…”

Macroecological drivers of zooplankton communities across the mountains of western North America

“…Oncorhynchus clarkii and O. mykiss) outside of their historical ranges and introduced exotic species that had previously not occurred (e.g. For instance, recent evidence suggests that the long-term effects of fish introductions may wane over time in more biologically diverse, warmer montane lakes (Messner et al 2013). We found that fish introductions were of less consequence to broad scale beta-diversity than anticipated (Fig.…”