Year of Award

2012

Document Type

Thesis

Degree Type

Master of Science (MS)

Degree Name

Wildlife Biology

Department or School/College

College of Forestry and Conservation

Committee Chair

Winsor H. Lowe

Commitee Members

Keith Nislow, Laurie Marczak, Lisa Eby

Keywords

early successional habitat, headwater streams, nonmetric multidimensional scaling, resource subsidies, salvelinus fontinalis, terrestrial invertebrate diversity, timber harvest

Publisher

University of Montana

Abstract

Spatial subsidies provide critical resources for organisms in receiving habitats, particularly when production in those habitats is low. While it is clear that terrestrial invertebrates provide a critical subsidy for trout, including eastern brook trout (Salvelinus fontinalis), we have limited understanding of what causes input and use of these subsidies to vary among streams. Among the watershed characteristics that may influence input and use of terrestrial invertebrates, I predicted that forest succession stage would be especially important due to differences in terrestrial invertebrate biomass in early and late successional habitats. To test this prediction, I measured terrestrial invertebrate biomass, input to streams, and use by resident brook trout in 12 first and second-order watersheds in northern New Hampshire, USA, representing a range of early successional habitat coverage (0-52%). I also measured invertebrate diversity and abundance in early and late successional habitats to assess the importance of habitat heterogeneity for forest invertebrate communities. Within the study watersheds, terrestrial invertebrate biomass, diversity, and abundance were significantly higher in early successional habitats than late successional habitats. However, biomass of terrestrial invertebrate inputs to streams was unrelated to the percent early successional habitat in the watershed, and both watershed and reach-scale forest characteristics were unrelated to percent terrestrial invertebrates in brook trout diets. Surprisingly, benthic invertebrate biomass was strongly, negatively related to the percent terrestrial invertebrates in brook trout diets, suggesting that productivity in the aquatic environment may influence the degree to which brook trout use terrestrial invertebrate subsidies. Overall, these results show that terrestrial invertebrate biomass is greater in early successional forest habitats, but that increasing the percent early successional habitat in watersheds does not influence the magnitude of this subsidy, or use by brook trout. While more research is needed on the factors influencing dietary preferences of salmonids, these results highlight the influence of in situ invertebrate production on use of terrestrial resources. Although terrestrial invertebrates may be an important food resource for salmonids, my results show that in-stream productivity can influence the relative importance of these allochthonous resources to aquatic consumers.

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© Copyright 2012 Matthew Kestrel Wilson