Multiple stressors in rotifer communities: : Effects of predation, climate change, and brownification

Sammanfattning: Most organisms on Earth live in an environment where they are exposed to multiple pressures, including predation and climate change. In many aquatic ecosystems, organisms have to handle additional challenges such as brownification, co-occurring with climate warming. Despite the growing recognition of impacts of climate warming or brownification on the freshwater communities, little is known on how synergistic effects from multiple environmental changes will affect community dynamics in freshwater ecosystems. In this thesis I investigate the effects of predation, climate changes, and brownification on the rotifer community dynamics.I show that predation has strong effects not only on population growth but also on inducible morphological defenses in rotifers. Larval fish feed extensively on rotifer prey and reduces spine length of a common rotifer (Keratella cochlearis) both through induction of shorter spines and selective predation on long-spined individuals. Furthermore, I demonstrate that rotifer prey can detect and respond appropriately in opposite directions to different sizes and feeding modes of predators by being plastic in spine and body size.My studies show that rotifer community will start to establish earlier in spring under a climate-warming scenario, whereas it would also decline earlier due to increased predation pressure. Furthermore, I show that in a future climate scenario with increased temperature variations and frequency of extreme temperatures, predatory copepods benefit from heat waves due to their ability of initiating diapause at an almost adult stage and rapidly responding to temperature variation, while rotifers suffer from a higher predation pressure. Hence, in a broader perspective my studies suggest that differences in life history traits will affect predator-prey interactions, and consequently alter community dynamics, in a future climate change scenario. However, the effects of brownification on establishment and growth in the rotifer community were less pronounced, or even negligible.