PARENT SESSION
Oral Session # 20: Biogeography II: Microorganism and Insect Communities.
Presiding: R Winfree
Tuesday, August 5. 8:00 AM to 11:30 AM, SITCC Meeting Room 106.
Boundary permeability to marine subsidies affects arthropod community structure on Gulf of California islands.
Anderson, Wendy*,1, Bethmann, Cory1, Wait, Alexander2, Allfree, Leslie3, 1 Drury University, Springfield, MO, USA2 Southwest Missouri State University, Springfield, MO, USA3 National Center for Ecological Analysis and Synthesis, Santa Barbara, CA, USA
ABSTRACT- Cross-ecosystem flux of energy, nutrients, detritus, and prey can have substantial impacts on population and community dynamics in recipient systems. Such fluxes may be inhibited or facilitated by the physical structure of the interface between the two systems. Differential permeability of ecosystem boundaries to mobile resources may partially explain distribution and abundance of species in the recipient systems. We assessed the arthropod community composition and relative contribution of marine-derived resources in their diets along 16 shore-to-inland transects established from beach- or cliff-type shorelines on desert islands in the Gulf of California. Total density of arthropods was highest along transects originating from low-angled beaches, which receive much marine macroalgae. Amphipods and spiders dominated these communities, with high densities maintained up to 25 m from the shore, whence they declined to typical inland densities. Beetles and ants became relatively more common further inland. Amphipods and spiders exhibited enriched 13C (indicative of marine-derived diets), but these signatures tapered off in individuals trapped further inland. In communities along transects originating at high-angled cliff shorelines inhabited by seabirds, total densities were lower than that on the beach transects, and the communities were dominated by beetles and ants. All guilds exhibited high 15N values, which indicate either direct or indirect consumption of seabird products. Neither density nor diet patterns varied along the 50m transects on bird inhabited cliffs. On transects from cliffs not inhabited by seabirds, total densities were lowest, and communities were dominated by amphipods and beetles in the first 2 meters, and by ants further inland. 13C and 15N isotopes indicated very little consumption of marine-derived resources. These results suggest that communities living on islands or other isolated habitats, or those living near the interface of two ecosystems may be distributed unevenly in response to differential permeability of ecosystem boundaries to allochthonous resource subsidies.
Key words: allochthonous input, isotopes, boundary permeability, arthropod communities