COS 86-3 - Zooplankton community responses to interannual climate variation across an elevational gradient

Background/Question/Methods

Climate change has profound effects across the globe by altering average environmental conditions as well as their variability. Shifts over the past decades show distinct patterns on different temporal scales – e.g., daily, seasonal, interannual. Climate models predict an even more extreme future, with sustained periods of drought punctuated by intense precipitation events and a shift toward more rain and less snow with greater evaporative losses. The response of communities to this variation depends on local environmental or ecological context. For example, zooplankton communities vary with elevation in mountain lakes without fish predators but contain similar species across all elevations in lakes with introduced trout. These results indicate that local biotic or abiotic forces can either magnify or dampen the sensitivity of aquatic communities and ecosystems to climate. To test the relative sensitivity of lake communities to environmental variability, we analyzed nine years of zooplankton and limnological data from 70 lakes in the California Sierra Nevada. We examined interannual variation in elevational turnover in zooplankton community composition. Next, we examined temporal turnover in zooplankton composition within lakes, and how it varied among lakes at different elevations, with and without predators.

Results/Conclusions

Tremendous interannual environmental variation occurred within the nine-year study period, encompassing both the wettest and second driest year on record. Precipitation largely fell as snow and impacted water temperature – wet years had colder water at high elevation and warmer temperatures at low elevation compared to drier years (ANCOVA, p=0.003). Water transparency was reduced and zooplankton abundance increased in wet years compared to drier years (Secchi depth, p=0.002; abundance, p=0.006). Zooplankton community composition turnover across elevation was similar among all years, though there was a tendency for greater spatial turnover in wet years (Slope of NMDS1 scores regressed against elevation as a measure of turnover; precipitation p=0.2). Finally, zooplankton communities showed greater temporal turnover in lakes at high elevation and lakes without fish (elevation, p=0.048; fish, p=0.044). Our results suggest that high elevation lakes face the most extreme climate change and are the most sensitive to interannual variation in climate. Understanding the spatial signature of climate change is crucial for ecological forecasting; this work reveals how environmental conditions mediate community shifts in mountain lakes.