Global change and algal diversity - a laboratory long-term experiment

Global change can alter diversity through elevated average temperatures but also by enhanced temperature variability. In a long-term microcosm experiment we examined the effects of different temperature regimes in combination with consumer presence or absence on phytoplankton communities. On the one hand the algal communities were kept in temperatures simulating the time course of a lake from temperate zones in our days, on the other hand of a lake about 100 years later with higher temperatures, especially in winter. We also manipulated the temperature variability by increasing or decreasing the main temperature every second week for half of the treatments. The experiment ran for 16 months and revealed that all three factors significantly influenced the dynamics of phytoplankton biomass, abundance, species richness, and evenness. Phytoplankton coexistence was enhanced by higher temperatures and grazer presence, phytoplankton biomass and abundance increased with higher temperatures and decreased with grazers, and temperature variability increased phytoplankton abundance. Interactions were also found between all combinations of the factors indicating complex ecological processes.