Document: AND-3-59-73

Reciprocal subsidies to forest birds and stream fishes by across-habitat prey flux.

NAKANO, S.* ¹ and M.MURAKAMI ²

Kyoto University, Hirano, Kamitanakami, Otsu, Shiga 052-2113, Japan ¹
Hokkaido University Forests, Takaoka, Tomakomai, Hokkaido 053-0035 Japan ²

Abstract:
Because productivity in a local habitat generally fluctuates seasonally, peak productivities in juxtaposed habitats can be asynchronous. If decoupled fluctuations reverse the productivity gradient and the direction of energy transfer between contiguous habitats, local communities in both habitats could be subsidized reciprocally and alternately. In a deciduous forest and stream ecotone, aquatic insect emergence peaked around spring, when terrestrial invertebrate biomass was low. In contrast, terrestrial invertebrate input to the stream occurred primarily during summer, when aquatic invertebrate biomass was nearly at its lowest. Accidental inputs of terrestrial invertebrates are known to be a major prey category directly available for stream consumers such as fish. Inversely, previous studies have often argued that riparian forests generally support greater species diversity and population abundance of terrestrial consumers than adjacent upland habitats, although the mechanisms responsible for this edge effect have remained poorly understood. Riparian consumers, e.g., birds, bats and spiders, may benefit from energy transfers gained from aquatic insects emerged from streams. Such reciprocal, across-habitat prey flux alternately subsidized both forest birds and stream fishes, accounting for 25.6% and 44.0% of the annual total energy budget of the bird and fish assemblages, respectively. Seasonal contrasts between allochthonous prey supply and in situ prey biomass determine the importance of reciprocal subsidies.

Keywords: across-habitat prey flux

This abstract is being presented at: 11:10 AM in session:
Symposium # 3: Linking Communities Across Ecosystem Boundaries: A Symposium in Memory of Gary A. Polis.