Document: FRA-3-15-5

Subsidies make strange partners: The effects of seabirds on terrestrial detritivores.

SANCHEZ PINERO, F.*

University of California at Davis, Davis, CA 95616 USA ¹

Abstract:
Organisms moving in a landscape link different habitats as prey, predators or transporters of nutrients and energy from one habitat into another. The impact of such organisms on the dynamics of the recipient habitat is influenced by differences in productivity between the habitats. On island ecosystems in the Gulf of California, where an unproductive desert juxtaposes to a highly productive ocean, seabirds are a major conduit bringing marine productivity to land in the form of guano and carrion. Seabirds directly and indirectly affect the abundance of a dominant group of detritivores, tenebrionid beetles. Tenebrionid densities vary by three orders of magnitude among islands; they are more abundant on islands where seabirds roost and nest than on other islands and on mainland sites. In addition, within nesting islands beetles are most abundant in areas influenced by seabirds, and tenebrionids are more dense inside versus outside colonies. Seabirds have direct and indirect effects on the abundance of these detritivorous beetles. On roosting islands, effects are mainly indirect via guano, which enhances primary productivity and increases availability of plant detritus, a food resource for tenebrionids. In contrast, on nesting islands, effects are primarily direct via seabird carrion, which tenebrionids scavenge, whereas indirect effects via guano are less important on these islands. Increases in these primary consumers indirectly facilitate high densities of many predators. By providing energy and nutrients to fuel a diverse array of consumer populations, seabirds are central to the dynamics of these island ecosystems. Because consumers cannot influence the renewal rate of their allochthonous resources, the dynamics of these consumers and their food webs are largely donor-controlled.

Keywords: Detritivorous tenebrionid beetles, donor-control,seabirds, spatial subsieies.

This abstract is being presented at: 9:50 AM in session:
Symposium # 3: Linking Communities Across Ecosystem Boundaries: A Symposium in Memory of Gary A. Polis.