Research objectives and content
Fish communities in northern European lakes are dominated by perch and roach. Perch become piscivorous with age, after going through planktivorous and bethivorous stages, while roach is mainly a planktivore. Habitat structure has prominent effects on competitive abilities and predator-prey interactions between the two species, determining ultimately their relative distribution and abundance. In most fish populations predator-induced mortality during early life stages may account for substantial variation in year-class strength, and may have important consequences for population and community dynamics. In many aquatic systems the main predators on fish larvae and juveniles are large fish, frequently adults of the same species. Since larval and juvenile fish undergo quick growth and fast development of sensory systems and swimming capabilities their vulnerability, for a given predator size, is expected to first increase (due to increasing conspicuousness) and then decrease (due to better escape responsiveness). The effects of predator and prey sizes, habitat structure
and alternate prey on predation mortality rates of small fish are well documented. However, it is not clear how the interaction of these factors affects predation mortality rates of prey fish and how this occurs along a continuous range of prey sizes. This project will study predation mortality rates of early stages of perch and roach as a function of their size, predator (piscivorous perch) size, habitat structure, and prey species assemblage. For this purpose the effects of the different factors on mortality rates will be studied under experimental laboratory conditions in order to quantify these relationships. Laboratory experiments will also be used to investigate in detail the predator-prey interaction during the attack and prey manipulation episodes. Finally, the laboratory results will be compared to field observations (whole lake experiments), which will show how well small scale experiments can be extrapolated to whole systems. Training content (objective, benefit and expected impact)
My work up to the present has been centered on different aspects of the biology and ecology of brown trout, based on fish sampling in streams, and including some experimental work on predation. The proposed post-doctoral study will expand my development as a scientist by providing an opportunity to go deeply into experimental work (on which the host group has considerable experience), within the context of a rich background of experimental and sampling based work. It will also provide me an opportunity to work with different fish species (subjected to different climatic conditions), and lakes in contrast with streams. The project proposal fits in with the host group interests, and is a key component of the modelling efforts on size-structured interactions currently underway. With respect to my future goals, I hope to obtain substantial experimental and theoretical expertise from the post-doc stay, and eventually be able to translate similar studies to local systems within my own country.