ИСТИНА

Food limitation (bottom-up effect) and predation pressure (top-down effect) are among the major factors driving population dynamics and shaping community structure. There are a number of methods to assess the relative role of the two effects; one of the most popular is the factorial-design experiment. Recently, an alternative approach has been proposed (Polishchuk et al., 2013), which puts these effects in a more dynamic context. The approach is particularly tuned to cladocerans. Under this approach, birth rate, which is a major population-dynamics parameter, is considered a hub linking the effects of food and size-selective predators (e.g. planktivorous fish) to demographic characteristics of the population – fecundity and proportion of adults, respectively. Consequently, the relative impact of top-down vs. bottom-up effects is assessed through the ratio of contributions, R, of the proportion of adults (ConA) and fecundity (ConF) to change in birth rate. Recently, the approach has been tested in laboratory experiments on Daphnia (Polishchuk et al., 2013). Here we test it in the field on another cladoceran, Bosmina longirostris, and find the results to be consistent with those obtained in the laboratory. We conclude that the method has the potential to measure the relative strength of top-down vs. bottom-up effects in natural populations of cladocerans.