Tests of Functional Equivalence Among Aquatic Predatory Vertebrates
Chalcraft, David Richard
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Permalink
https://hdl.handle.net/2142/85343
Description
Title
Tests of Functional Equivalence Among Aquatic Predatory Vertebrates
Author(s)
Chalcraft, David Richard
Issue Date
2002
Doctoral Committee Chair(s)
Batzli, George O.
William J. Resetarits, Jr
Department of Study
Biology
Discipline
Biology
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Biology, Zoology
Language
eng
Abstract
Many ecological studies and theories assume that species occupying similar trophic positions perform similar functions on population, community, and ecosystem dynamics (i.e., they are functionally equivalent). This is particularly true for models predicting (i) the effects of one trophic level upon another and (ii) the consequences of biodiversity loss. Currently, the loss of biodiversity represents one of the most important issues facing our planet. Understanding how different species contribute to the functioning of natural ecosystems is critical to predicting the consequences of species loss. Using artificial ponds, I conducted experiments designed to address questions regarding the issue of functional equivalence of aquatic predatory vertebrates. I specifically focused on the response of larval anurans to (i) variation in the identity of predator species, (ii) variation in trait characteristics possessed by predators and (iii) variation in the total biomass and density of predators present. I found that most predator species differed in their effects on larval anurans. Such variation in the effects of different predators indicates that there is substantial variation in the quality of potential habitats within the landscape. Furthermore, I have shown that it may be difficult to predict which species will be most similar in their effects because different components of the food web respond differently to different predator traits. Thus, the old assumption that species who look alike and act alike will have similar functional roles in a community is not supported because different prey species do not view predators in the same manner. I also present evidence that intraspecific variation in average body size among predator populations results in a species having a different effect on larval anurans, even if the populations have a similar total biomass or density. It appears that these differences arise from size specific differences in metabolic rate and in response to density-dependent factors. Hence, different populations or species will only be functionally equivalent with one another under a limited set of ecological circumstances.
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