PARENT SESSION
Poster Session #29: Animal Population and Community Ecology.
Wednesday, August 8, 2001. Presentation from 3:30 PM to 5:00 PM. Exhibition Hall

Relaxation of tropical avian communities on recently created land-bridge islands.

Feeley, Kenneth¹, ¹

ABSTRACT- Upon fragmentation of once contiguous habitat, faunal communities undergo a period of relaxation, or species loss, before achieving a new equilibrium. The rate of relaxation is hypothesized to correspond to several physical parameters of the habitat fragment, including patch area, degree of isolation, and relative amount of edge. In 1986, Venezuela completed construction on the Raul Leoni Dam, inundating 4300 km^2 of hilly terrain. This flooding resulted in the formation of hundreds of "land-bridge" islands which serve as an ideal model system for studying the effects of fragmentation and the process of relaxation. In 1993 and 2000, the avifauna nesting on a sample of 12 islands and 1 mainland site were censused. Study islands ranged in size from 0.6 to 350 ha and were isolated from the mainland by as much as 7 km. In the seven-year interval between censuses, species richness decreased significantly in almost all sites (mean decrease in species richness of 45.66%, st.dev. = 35.11%). Aggregate bird densities also decreased significantly (mean decrease in density of 36.83%, st.dev. = 46.11%). Relaxation rates were calculated for each of the study islands using a model assuming exponential decay in species number. Contrary to predictions, relaxation rates did not show any significant correlation to patch area, isolation, or relative amount of edge. This lack of correlation may be due to the vagile nature of birds and high rates of colonization and extinction on the islands.

KEY WORDS: faunal relaxation, fragmentation, land-bridge islands