Resource subsidies to arthropod food webs at a pond-forest boundary

Kraus, Johanna Marie, Department of Biology, University of Virginia
Wilbur, Henry, Department of Biology, University of Virginia
Galloway, Laura, Department of Biology, University of Virginia
Macko, Stephen, Department of Environmental Sciences, University of Virginia
Taylor, Douglas, Department of Biology, University of Virginia

Resources that move across ecosystem boundaries have been shown to subsidize recipient consumers and have complex consequences for recipient food webs. Emergence of aquatic insects onto land and accidental input of terrestrial arthropods into water are two important pathways by which protein-rich resources move between freshwater and terrestrial habitats. In this dissertation, I used field observations, conceptual modeling, field experiments and stable isotopes to understand the role of arthropod prey moving between a pond and forest habitat in generating the temporal and spatial patterns of predator abundance, size, reproduction and diet seen on land and in the water. The wolf spiders, dragonfly larvae, newts and crayfish living in and around two small permanent ponds in the southern Appalachians are a well-defined system within which to examine these ideas.

Aquatic insect movement to land was predictable only at the whole pond level, whereas terrestrial arthropods falling into the water could be manipulated locally within ponds. Wolf spider per capita mass and the proportion that were reproductive declined within enclosures where aquatic insects had been reduced by 50%. Wolf spiders at the edge of the pond consumed aquatic resources' as demonstrated by a temporal shift in isotopic signatures which paralleled the change in isotope enrichment in aquatic insects emerging from the pond after the enclosures had been isotopically labeled with 13C. Furthermore, the response of wolf spiders to aquatic insect prey differed among ponds and species life histories. Dragonfly larvae seemed to consume more terrestrial resources when more were available, as evidenced by isotopic data, but their abundances were not influenced by a reduction in terrestrial input. The reduced input also appeared to between crayfish and dragonfly larvae.

A conceptual model of donor and recipient food web productivity and types of effects of subsidies suggested that two-way movement should be important at the pondforest interface. Results of this dissertation lend some support to this hypothesis but emphasize that the influence of subsidies on predators varies by taxa, the size and productivity of the aquatic habitat and the spatial scale of the subsidy.

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PHD (Doctor of Philosophy)
community ecology, stable isotopes, aquatic insect movement, food webs, ecosystem boundaries

Digitization of this thesis was made possible by a generous grant from the Jefferson Trust, 2015.

Thesis originally deposited on 2016-02-18 in version 1.28 of Libra. This thesis was migrated to Libra2 on 2017-03-23 16:34:10.

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