Graduate Thesis Or Dissertation
 

Functional relationships among vegetation, nocturnal insects, and bats in riparian areas of the Oregon Coast Range

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  • Vegetation provides food for many insects, and many insects serve as food for bats. We investigated the linkages among these three trophic levels in riparian areas throughout the Oregon Coast Range by examining the influence of vegetation cover, composition, and structure on the activity of nocturnal insects and bats, the influence of insect abundance on activity of bats, and the diets of bats. Vegetation characteristics at the stream reach spatial scale explained more variation in bat activity than did vegetation characteristics measured at larger spatial scales. Vegetation characteristics most closely associated with bat activity varied among species of bat, included both canopy and shrub attributes, and apparently operated through constraints imposed by vegetation structure on bat flight capabilities rather than through regulation of the distribution of insect prey abundance. The two orders of insects most frequently consumed by bats were Lepidoptera and Diptera. Three species of bat fed predominantly on small insects likely of aquatic origin, and activity of these species was correlated with local abundance of small insects. The seven remaining species of bat fed predominantly on larger, terrestrial insects, and their activity was not correlated with local abundance of insects. Variation among stream reaches in the number of captures and biomass of the six most commonly captured orders of insects (Diptera, Lepidoptera, Trichoptera, Ephemeroptera, Coleoptera, and Hymenoptera) was better explained by cover of deciduous canopy than by any other vegetation characteristic investigated. The number of captures and biomass of these insects increased as deciduous canopy cover increased. Canopy composition explained variation in macro-moth community composition as well: species richness and cover of canopy trees and of shrubs were associated with variation in moth species composition. Number of moths captured, biomass, and Shannon’s species diversity were greater in deciduous- than conifer-dominated stream reaches. Deciduous shrub and canopy trees play an important role in the determination of nocturnal flying insect abundance and community composition. Management activities that promote deciduous vegetation in riparian areas in this region are likely to help maintain biodiversity and abundance of nocturnal insects, which in turn serve as food resources for bats.
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