The relevance of reproductive characteristics of zooplankters to experimental studies in outdoor enclosures

The zooplankters Daphnia pulex, Diaptomus siciloides, Diaptomus clavipes and Acanthocyclops vernalis were manipulated in outdoor tanks (1 m³) for long term (six months) experiments. There were distinct patterns of variability among the species which were mostly independent of treatment effects (e.g. fish predation intensity, in one experiment). Diaptomus showed greater within-treatment variability (coefficient of variation CV = 1.2) than did Acanthocyclops and Daphnia (CV = 0.5). The extinction of calanoids in some tanks was partly responsible for this variability. Acanthocyclops and Daphnia never were extinct, but did occasionally colonize (contaminate) tanks to which they had not been intentionally introduced. Colonization and extinction events were related to reproductive characteristics of the species involved, which also determine the minimum critical densities necessary for population establishment and persistence.Manipulation of zooplankters in outdoor enclosures must take into account the species life histories, reproductive mode and behaviour. Species must be inoculated in numbers larger than their minimum critical densities and measures must be taken to avoid contamination with unwanted species. Replication of treatments should be adapted to these conditions and this may be unequal in an experiment dealing with different species.This research was supported by the Joint Doctoral Program in Ecology at San Diego State University and by a U.S. National Science Foundation Doctoral Research Improvement Grant (BSR 84-13983). The relevance of reproductive characteristics of zooplankters to experimental studies in outdour enclorures.This research was supported by the Joint Doctoral Program in Ecology at San Diego State University and by a U.S. National Science Foundation Doctoral Research Improvement Grant (BSR 84-13983). The relevance of reproductive characteristics of zooplankters to experimental studies in outdour enclorures.