The effect of increased temperature variability on community dynamics depends on trophic level position

Background/Question/Methods

Climate change research has demonstrated that changing temperatures will have an effect on community-level dynamics through changes in species’ survival rates, shifts in species’ distributions, and ultimately, mismatches in interactions within a community. However, most of this work has focused on increasing temperature, and it is still not known how the variation in temperature and temperature extremes will affect community dynamics. We used the model aquatic community held within the leaves of the carnivorous plant, Sarracenia purpurea, to test how food web dynamics will be affected by temperature variation and temperature extremes. Before opening each pitcher/leaf cavity is sterile. After filling with rainwater, bacteria, protists and rotifers form a food web within these detritus-fueled ecosystems. We tested the community response (change in protozoan diversity, bacterial density, and top predator mortality) to increasing temperature variability. We collected water from S. purpurea inquiline early and late succession communities in four sites (2 in North America and 2 in Switzerland) that matched in average July temperature. We then created a common garden experiment in which replicates of these communities underwent either high daily temperature variation or normal daily temperature variation. The average temperature of the treatments was kept the same.

Results/Conclusions

High temperature variation affected the bottom trophic level, with bacterial densities of naive communities in high variability conditions lower than non-naive communities. This effect, however, was reversed when compared with communities that underwent normal temperature variation. One possible explanation of these results could be due to a lack of top-down control in the naive, high variation communities. For the intermediate trophic level species (the protozoans) that underwent high temperature variation, late succession communities had a much greater change in alpha-diversity throughout the time course of the experiment than early succession communities. A similar trend was also observed for protozoan community composition. With communities in early succession mainly composed of pioneer species, it can be predicted that they will be less affected by environmental changes than species in late successional stage communities. Overall, these results suggest that communities are affected by temperatures that undergo high daily variation but the effects may be dependent on the successional stage of the consumer community and if the prey community is top-predator naive. It is therefore important to know the particular aspects of the community if we are to predict how temperature variation will alter future community dynamics.