Date of Award

Fall 2007

Project Type

Dissertation

Program or Major

Natural Resources and Environmental Studies

Degree Name

Doctor of Philosophy

First Advisor

Kimberly J Babbitt

Abstract

To test the effects of brook trout (Salvelinus fontinalis) on stream macroinvertebrates and salamander larvae, I conducted a large-scale manipulation of trout presence in the White Mountain National Forest, NH. I included 9 streams in the study: 3 with trout, 3 without fish, and 3 without fish to which I added trout. I measured invertebrate benthic density before and 1 yr following trout translocation and drift density before, shortly following, and 1 yr following trout translocation. I also measured larval two-lined salamander (Eurycea bislineata) density and day and night activity on the stream substrate surface before and 1 yr following trout translocation.

Trout presence did not affect invertebrate benthic density, drift density, or drift periodicity; however, a few taxa reduced their drift with trout. Ordinations identified patterns in benthic invertebrates that varied by time and space and drifting invertebrates that varied by time. Salamander density and daytime activity decreased following trout addition to streams, and salamander activity shifted from aperiodic to more nocturnal with fish.

Among the attempts to understand variation among stream predation studies are 3 models that address prey movement, prey behavior, and spatial scale. To analyze the relevance of the models, I compared the predator impact for each taxon with its propensity to drift, relative (trout vs. fishless streams) propensity to drift, and trout predation rate. I found no clear patterns. However, taxa with relatively high drift rates experienced relatively high trout predation.

In a small-scale laboratory experiment, I tested how brook trout and larval two-lined salamanders affected each other's prey consumption. Salamanders ate fewer prey with trout, but trout ate more prey in the presence of salamanders. The data suggest that as predators that often coexist with fish in streams, salamanders can influence invertebrate prey communities both directly and through density- and trait-mediated interactions.

Although trout had a clear impact on salamander density and activity, they had little impact on macroinvertebrates. Temporal and spatial changes in the invertebrate assemblage suggest that other factors are more relevant in this system at a large spatial scale.

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