Biotic relations affecting species structure in zooplankton communities

Abstract

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.

Spatio-Temporal Segregation of Cladocerans within aChara hispidaBed

“…It is difficult to identify the factors responsible for zooplankton patchiness; however, physicochemical parameters along with biological processes are involved (Semenchenko et al 2007). In the case of the organism segregation in time and space in the C. hispida stand of Lake Wielkowiejskie, several factors (oxygen concentration, nutrient availability, and fish predation) seemed to be involved.…”

Effects of constant and stepwise changes in temperature on the species abundance dynamics of four cladocera species

“…The astatic regime should be more favorable for their development than the stable regime, especially after a 4-4.5 • C decrease in temperature. In addition to high thermal lability, S. vetulus possesses a relatively high oxygen lability (LaBerge and Hann, 1990) and feeding plasticity, which is confirmed by the high growth rates of populations even at very low equilibrium concentrations of food, which results in a decrease in number being observed in other species (Semenchenko et al, 2005(Semenchenko et al, , 2007. Moreover, upon changes in the water temperature within the diapason of 12-25 • C S. vetulus is able to recover its carbon assimilation rate quickly (Bevan et al, 1980), which, as the authors of this paper believe, indicates the ability of this species to quickly acclimate at various temperatures.…”

Impacts of large-bodied crustaceans on the microbial loop

“…and S. vetulus overlap (algae, bacteria, protists), and they compete in nature, e.g. in Lake Naroch (Semenchenko et al, 2007). Adult M. albidus are commonly predators (Rey et al, 2004); however, early nauplii and copepodites stages can graze on phytoplankton and ciliates (Adrian & Schneider-Olt, 1999) such that they also likely compete with the other two alien taxa at least during some life stages.…”