UBC Theses and Dissertations
The ontogenetic ecology of the signal crayfish, Pacifastacus leniusculus, in a small temperate stream Bondar, Carin Anne
Organisms that undergo ontogenetic niche shifts, changes in behavior or resource use with respect to developmental stage, can have disparate ecological roles through development. This thesis examines the ontogenetic ecology of the signal crayfish, Pacifastacus leniusculus (Dana) using field and laboratory based experimentation as well as a detailed population study. I initially researched the roles of ontogenetic stage and density of crayfish, and how this can affect the intensity of their roles within a community. An enclosure experiment was conducted in a small stream (Spring Creek) in Malcolm Knapp Research Forest. Both juvenile and adult crayfish were found to have major effects on the surrounding community; however, these effects were independent of ontogenetic stage. Gut and stable isotope analyses were employed to determine the primary food sources of the crayfish from this study in an attempt to establish the mechanism behind their effects on the stream community. Aspects of the diet were further investigated in the laboratory by examining growth-rate of both juveniles and adults that were provided with leaves, wood or invertebrates. From the latter results, another experimental study was designed in order to examine the effects of predators (adult crayfish or adult cutthroat trout (Oncorhynchus clarki (Richardson)) on the feeding behavior of juvenile crayfish, as their natural diets contained a large proportion of energetically poor food sources. Based on the fact that both predators were found to have negative effects on feeding behavior juvenile crayfish, a field experiment was undertaken to explore the ontogenetic relationships between signal crayfish and cutthroat trout. I found a reciprocal negative effect of adults of one species on juveniles of the other, as well as a negative effect of juvenile crayfish on juvenile fish. In order to contextualize the work accomplished in the first part of this thesis, I undertook a population mark-recapture study which provided information on crayfish density in Spring Creek, as well as ontogenetic aspects of survival, movement and microhabitat choice. Overall, the work presented in this thesis represents a substantial contribution to our knowledge of the ontogenetic ecology of the signal crayfish.
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