Abstract
Understanding when small- or large-bodied cladocerans dominate zooplankton communities has received considerable debate over the past 50 years. While a large body of research has proposed that large-bodied species are superior competitors over small-bodied species, other studies have shown that small-bodied species can dominate at least under some environmental conditions. We tested the hypothesis that dominance by small- and large-bodied cladocerans varied in response to the coupled effects of food supply and temperature. Laboratory experiments with poly- and monocultures of small- and large-bodied cladocerans were performed at three temperatures (16°C, 22°C and 27°C) and with varying amounts of food supply. The results of the experiments showed that the small-bodied species (Ceriodaphnia quadrangula) dominated at low food supply and higher temperature, while the large-bodied species (Daphnia magna and Daphnia pulex) in contrast dominated at lower temperature and higher food supply. Furthermore, although there were variations in the relative biomass of the small- and large-bodied cladocerans in the polycultures, C. quandrangula replaced the two larger Daphnia species when they declined in biomass at low food supply. Species replacement in response to temperature and food supply helped to maintain the relatively constant level of total cladoceran biomass in the polycultures which was the most pronounced at the intermediate temperature. We suggest that the observed changes in dominance were similar to facilitative replacement rather than competitive exclusion. Physiological processes such as clearance rates can help to promote the succession of large- and small- bodied populations within a community along gradients of temperature and food availability.
Highlights
A large body of research has focused on understanding the interactions between large- and small-bodied cladocerans
High temperature combined with a high level of food supply resulted in conditions that favored D. magna and D. pulex; as the experiment progressed there was a reduction in food supply that favored C. quadrangula
While the biomass of the large-bodied D. magna began to decrease in response to the thermal and resource conditions, these conditions appeared to become more favorable for C. quadrangula which started to increase in biomass
Summary
A large body of research has focused on understanding the interactions between large- and small-bodied cladocerans. Brooks and Dodson [1] proposed that in the absence of fish predation, large-bodied species were competitively superior to small-bodied species (i.e., the Size Efficiency Hypothesis; [1]). While many studies have supported the predictions of the Size Efficiency Hypothesis [2,3], there is a large body of research showing that small-bodied cladocerans are superior competitors [4,5,6,7]. Based on these contradictory results, it is possible that dominance by either large- or small-bodied cladocerans is dependent on environmental conditions. Moore et al [13] hypothesized that the competitive ability of OPEN ACCESS
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