a b s t r a c tIn 11 lakes from cold and warm regions we studied the content of highly unsaturated fatty acids (HUFA) in seston (<130 m) and crustacean zooplankton using gas chromatography-mass spectrometry. An increase of temperature correlated with a decrease of HUFA content in zooplankton. A multivariate canonical correlation analyses revealed, that the decrease of HUFA content was related with a decrease of per cent of copepods in zooplankton communities, which are known to have higher HUFA levels in their biomass, than cladocerans. This means that temperature primarily affected the HUFA levels indirectly, via changing of taxonomic structure of zooplankton community, while the homeoviscous adaptation of zooplankton individuals had comparatively lower importance. As found, water temperature was better predictor of HUFA contents of zooplankton, than the fatty acid composition of seston. Thus, it can be predicted, that a probable climate warming will decrease the content of the essential HUFA in freshwater zooplankton with possible negative consequences for animals of higher trophic levels.
Mathematical modelling and laboratory experiments were used to study how exploitative competition and predation influence the species structure in cladoceran community. For five species of Cladocera (Sida crystallina, Daphnia magna, Simocephalus vetulus, Daphnia longispina, and Diaphanosoma brachyurum), representing a gradient of body size, population characteristics were described as functions of food concentration. Abundance dynamics were simulated in mixed species cultures and invasion experiments under different levels of food supply corresponding to oligo-, meso-, and eutrophic conditions. Separate simulations were also run including and excluding (fish) predation. The competitive ability of each species was estimated as the values of the population equilibrium food concentration. Simulation results showed that for the no-predator scenario, increases in the level of food supply promoted species coexistence while under lower food concentrations only one species remained at the end of the simulation runs. When predation was allowed, the number of species that coexisted at the end of the simulations increased up to four species, indicating that predator pressure facilitated species coexistence because it shortened periods of food depletion. Simulation results were verified in laboratory experiments which suggested that population equilibrium food concentration can be used as an estimate of competitive ability. Finally, species structure and relative abundance in Lake Naroch (Belarus) during the summer of 2004 was found to be consistent with our results from computer simulation and laboratory experiments with regard to competition and predation impacts on zooplankton community.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.