Temperature effects on zooplankton community dynamics depend on the competitive environment

Background/Question/Methods

Climate change exposes biological communities to elevated temperatures that can alter community dynamics, a phenomenon that could be exacerbated in highly connected communities by facilitating the colonization of competitively dominant species. In more isolated communities, colonization rates will be relatively low, potentially slowing the effects of temperature changes on community composition. How these dynamics play out in aquatic zooplankton communities is unclear, despite the sensitivity of ectothermic species to climatic regimes. To test how temperature influences the effects of competitive interactions on population- and community-level dynamics, we conducted a mesocosm experiment with zooplankton (copepods, cladocerans, rotifers) that originated from three regions, which spanned 1900 km gradient in western Canada. The experiment consisted of a fully crossed factorial design: three temperatures x six competitive treatments (each region alone and in competition with each other region). Growth rates and turnover at different temperatures were used to determine if adding novel species’ altered the persistence of resident species’, and if these effects are mediated by temperature. 

Results/Conclusions

The results of our study indicate that taxa respond differently to changes in temperature and their competitive environment. Growth rates for all taxa were over twice as high under local temperature conditions, except for rotifers where communities from low latitude regions had low growth rates, despite being exposed to their local temperature. The beta-diversity of low latitude cladoceran communities was initially high, but began to stabilize after two months. The addition of new species increased the population variance for all regions, leading to unstable community dynamics, but the magnitude of the effect depended on temperature. Our preliminary results suggest that, at least in the short term, local adaptation may constrain high latitude species from taking advantage of elevated temperatures. Moreover, colonization by new species may disrupt community dynamics and lead to compositional shifts that could not be detected or predicted by evaluating temperature effects in isolation. Overall, our work suggests that highly connected communities will be more vulnerable to the effects of climate change and that their specific responses to climate change are more difficult to predict.