Competition in zooplankton communities: Suppression of small species by Daphnia pulex1

Abstract

The hypothesis that a large zooplankton herbivore, Daphnia pulex, can competitively reduce the abundance of resident zooplankton when colonizing a community of small species was tested in two lakes. When introduced to enclosures in eutrophic Larimore Pond, D. pulex decreased phytoplankton abundance by an order of magnitude, resulting in drastically reduced densities of Tropocyclops prasinus and Mesocyclops edax, the two dominant crustaceans in the pond. Daphnia pulex was also added to enclosures in oligo-mesotrophic Dynamite Lake, along with nutrients, in a factorial design. Three Dynamite Lake zooplankters were reduced in density by D. pulex under both enriched and unenriched conditions: Bosmina Zongirostris, Trichocercu multicrinis, and copepod nauplii. Nutrient additions allowed these taxa to overcome some effects of competition with D. pulex. Daphnia pulex reduced the densities of copepods and rotifers common to both lakes more in eutrophic Larimore Pond than in unenriched Dynamite Lake enclosures.These results show that a large herbivore can reduce the density of some small zooplankton species and therefore contribute to the scarcity of small species in lakes dominated by large herbivores. Furthermore, the results suggest that the competitive effects of a large herbivore on rotifers and copepods may bc more pronounced in eutrophic systems because the large species can attain a higher population density, and subsequently alter the resource base to a greater extent, in eutrophic systems.Freshwater zooplankton communities typically are dominated by either large-or small-bodied species. Lakes containing abundant planktivorous fish contain mostly small species, the result of the elimination of large species by size-selective fish predation (e.g. Hrbacek 1962; Brooks and Dodson 1965;Lynch 1979). Fishless lakes are typically inhabited by large species, sometimes to the exclusion of small species (e.g. Brooks and Dodson 1965;Zaret 1980). Two hypotheses have been proposed to account for the scarcity (or absence) of small species in fishless lakes. One is that large herbivorous zooplankton, by monopolizing the food resources (mainly phytoplankton), competitively reduce the abundance of, or exclude, small species (the size-efficiency hypothesis by Brooks and Dodson 1965). An alternative hypothesis is that predation pressure, e.g.

Comparaison des communautés d'invertébrés entre des lacs avec et sans omble de fontaine (Salvelinus fontinalis) /

“…Also, many studies have demonstrated the competitive dominance of daphnids over smaller herbivores such as Keratella cochlearis (Neill 1984;Gilbert and Stemberger 1985;Arvola and Salonen 2001), Kellicottia sp. (Neill 1984) and copepod nauplii (Vanni 1986), which is consistent with our results.…”

The effect of Daphnia interference on a natural rotifer and ciliate community: Short‐term bottle experiments

“…Neil1 (1984Neil1 ( , 1985 showed that removal of Daphnia rosea from Gwendoline Lake enclosures caused marked increases in the fertilities and population densities of planktonic rotifers, mostly K. cochlearis and Kellicottia longispina. Vanni (1986) found that adding D. pulex did not significantly reduce populations of K. cochlearis and P. vulgaris in Larimore Pond and Dynamite Lake enclosures but did significantly suppress the Trichocerca multicrinis population in the latter enclosures. The absence of a significant Daphnia effect on most of his rotifer populations may be explained, however, by low and declining rotifer densities in both control and expcrimental enclosures at both sites, by quite low Daphnia densities in the experimental enclosures in Dynamite Lake, and by limi ted replication.…”

Relative vulnerabilities of natural rotifer and ciliate communities to cladocerans: laboratory and field experiments

“…Lampert et al, 1986;Vanni, 1986). In the enclosure experiment, mean cladoceran biomass was never greater than 25jig T '.…”