PARENT SESSION
Oral Session #32: Animal Community Ecology. Presiding: M. Weiss.
Tuesday, August 7, 2001. 1:00 PM to 4:45 PM. Hall of Ideas P&Q.
Faunal Effects on Floristic Diversity in a Lowland Neotropical Rainforest.
Sherman, Peter1, 2, 1 2
ABSTRACT- Data suggest that the land crab (Gecarcinus quadratus) affects adult vegetative diversity in a primary rainforest through selective seedling consumption. In Corcovado National Park, Costa Rica, G. quadratus lives in a fossorial population from one to six crabs per square meter within a band of coastal forest. This band extends 600 meters inland until a 30 meter wide transition zone that begins the extensive remainder of the forested National Park that is devoid of land crabs. The composition of dicotyledonous plants from the two adjacent zones (with and without crabs) are distinct: crabless-zone transects contained 97 dicotyledonous species representing 76 genera and 41 families; crab-zone transects contained 46 species representing 38 genera and 25 families. Despite the narrow zonal separation, the crabless-zone shared only 26.8, 30.3, and 53.7% of its species, genera and families respectively with the crab-zone; in contrast, crab-zone transects shared 56.5, 60.5 and 88% of their species, genera and families with the crabless-zone. This unilateral and abrupt diversity gradient suggests a powerful selection pressure in the crab-zone preventing the establishment of certain dicotyledonous species. A battery of exerperimental tests including two years of experimental crab exclusion suggests that G. quadratus is the causal mechanism reducing and limiting dicotyledonous seedling (and thereby adult) densities and diversities.
KEY WORDS: landcrab, rainforest, biodiversity, dicotyledons