Document: MAR-3-15-6

Responses of terrestrial consumers to emergent aquatic insects in a forested Northern California watershed.

POWER, M.E.* and W.E.RAINEY

University of California, Berkeley, CA 94720 USA ¹

Abstract:
We are studying the responses to river insect production of watershed consumers that differ in their abilities to track this food resource. In order of increasing mobility, these consumers are filmy dome spiders (Linyphiidae), tetragnathid spiders, cursorial wolf spiders (Lycosidae), fence and sagebrush lizards (Sceloporus occidentalis, Iguanidae), and vespertilionid and molossid bats. Emergent aquatic insects (and, during the dry summer, all insects) are most abundant over or immediately adjacent to the river, and decline exponentially upslope. With the exception of linyphiid spiders, all consumers studied show strong numerical responses to the river-to-ridge gradient in insect flux. Manipulations of the flux -- reductions with "subsidy shields", supplementation by algal mat manipulations or with lights at night -- produced short term tracking responses by lycosids, tetragnathids, lizards, and bats. Emergence rates and lateral fluxes of insects into watersheds vary as expected with watershed position, with lower emergence and reduced lateral spread in headwaters relative to downstream reaches. Bat tracking of aquatics at these positions appear to be influenced by species-specific foraging habitat preferences. Collectively, bats appear to be "over-aggregated" relative to insect prey over quiet pools, where they can forage without interference from turbulent water.

Keywords: trophic exchange, food webs, secondary productivity, numerical response, redwood forest, watershed ecology, aquatic insect emergence

This abstract is being presented at: 11:50 AM in session:
Symposium # 3: Linking Communities Across Ecosystem Boundaries: A Symposium in Memory of Gary A. Polis.