Environmental Instability and the Structure of Temporary Pond Zooplankton Communities
Thiery, Richard George
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https://hdl.handle.net/2142/77611
Description
Title
Environmental Instability and the Structure of Temporary Pond Zooplankton Communities
Author(s)
Thiery, Richard George
Issue Date
1981
Department of Study
Ecology, Evolution, and Conservation Biology
Discipline
Ecology, Evolution, and Conservation Biology
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Biology, Ecology
Language
eng
Abstract
Chapter I. Ideas relating environmental instability and community diversity are reviewed. The distinction is made between evolutionary mechanisms, which require very long periods of time to operate, and ecological mechanisms, which operate over shorter spans of time. As part of the discussion of ecological mechanisms, environmental instability is related to the concept of environmental harshness. Special emphasis is placed on the idea that predators of some ecosystems may be more vulnerable to harsh conditions than their prey.
Chapter II. The zooplankton communities of two temporary ponds (Center Pond and Edge Pond) in east-central Illinois were studied for three years. Although the ponds usually dry up in summer, as happened in each year of this study (1976-78), they did not dry between the 1975 and 1976 seasons. The 1977 season was unusually short due to low precipitation, and the 1978 season was delayed by a late thaw.
The salamander Ambystoma texanum bred only in Edge Pond in 1976, in neither pond in 1977, and in both ponds in 1978. This variation in breeding habits appears related to differences in vernal conditions. By means of an exclusion experiment it was demonstrated that Ambystoma larvae can reduce competition among the zooplankton and increase zooplankton diversity by enhancing the abundance of apparently inferior competitors (rotifers and copepods).
The abundance of the phantom midge, Chaoborus, is controlled by pond-drying and Ambystoma predation. Chaborus was abundant in Center Pond throughout 1976 due to the continuous pond-filling from 1975 and the absence of Ambystoma. As a result, most zooplankton, except for disfavored prey of Chaoborus, were eliminated. The disappearance of Ceriodaphnia from Center Pond in late 1978 also corresponded with rising Chaoborus density. Hence Chaoborus has a depressing effect on zooplankton diversity.
Ambystoma and Chaoborus are thus different both in their effects on zooplankton diversity and in their mode of vulnerability to environmental instabilty. Ambystoma larvae enhance zooplankton diversity and their presence is regulated by the demand of the adults for certain environmental conditions in a particular season (environmental contingency). Chaoborus larvae depress zooplankton diversity and their abundance is regulated, in part, by pond-drying (environmental inconstancy). Hence different components of environmental instability can, by altering the occurrence of predators with differing impacts, have different effects on zooplankton diversity.
Chapter III. Larval populations of Chaoborus americanus and Chaoborus albatus were studied for three years in two temporary ponds in east-central Illinois. Both species showed rapid development rates with at least three generations in an average season. In laboratory experiments, fourth-instar C. americanus had high feeding rates (up to 70 Ceriodaphnia per day). These high development and feeding rates are attributed to the warm temperatures, and possibility the ephemeral nature, of the ponds.
Chaoborus abundance is apparently controlled by mortality due to (1) pond-drying, and (2) predation by salamander larvae (Ambystoma texanum). In the unusual circumstance that Ambystoma fails to breed and the ponds do not dry between seasons, Chaoborus larvae may become so abundant that competition is severe, causing a decline in larval size. Under more normal conditions, competition is not so severe, but application of the laboratory feeding curves to field densities of zooplankton shows that Chaoborus predation can still have a significant impact on the zooplankton.
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