Species distributions are shifting globally with climate change, but forecasting these changes is challenging because the rate that communities respond depends on how physiological tolerances and species interactions combine to structure diversity. Because warming is accelerated in northern regions and diversity declines at higher latitudes, community-level responses to climate change may also vary across a latitudinal gradient. Terrestrial range shifts have already been documented, with species moving north as a consequence of warming during the last 50 years. How this plays out in aquatic systems, however, is less understood, despite their apparent sensitivity to climatic regimes. In this study we tested the impact of climate change on community composition, specifically asking (1) how has community composition and species distributions changed over time? and, (2) how does the magnitude of change vary with latitude and species richness? In 2011, we collected zooplankton from 43 lakes in western Canada across a 1600 km latitudinal gradient, from southern British Columbia to the mid-latitude Yukon, which had been sampled systematically over up to 80 years.
Results/Conclusions
The results of our study indicate that there is a negative relationship between community turnover and latitude, which is consistent with recent work in other geographic regions. However, we build on this by decomposing turnover into species gains and losses. Species gains occurred only in southern lakes, but there was no difference in the extinction levels across the gradient. The increased community dissimilarity in the southern lakes suggests that, despite relatively high species richness, this region is more easily invaded by new species. Overall, our results demonstrate that more diverse communities show greater compositional turnover through time. Species traits underlie the response of communities to climate change, and we demonstrate that differences in colonization but not extinction dynamics are driving compositional turnover across space. We propose two hypotheses for the greater inertia of northern regions, and outline ongoing experiments designed to test these hypotheses.