Oral Session - Quantitative Relationships Between Landscape Processes and Patterns and Wildlife - Morning Session Chair(s): Robinson, Vincent¹, ¹ University of Toronto at Mississauga, Mississauga, ON, Canada
Friday, April 2, 2004 9:00 AM - 11:00 AM Apollo Room 1-2

Bird assemblages in neotropical fragmented habitats: Multimodality in body size and complex allometries. Restrepo, Carla^*,1, Cuervo, Andres ¹, Anciaes, Marina², ¹ Department of Biology, San Juan, PR, USA² Department of Ecology and Evolutionary Biology, Lawrence, KS, USA

ABSTRACT- Body size is a universal currency with a great potential for understanding the impact of forest fragmentation on animal and plant assemblages given its well-known relationship with physiological, morphological, and population-level traits. When integrated across all species, the distribution of body size may be described as unimodal or multimodal, the former reflecting the existence of a single optimal size whereas the latter of several. Here we explore the possibility that multimodality in body size is intimately related with complex scaling relationships in which the scaling exponents do not remain constant over the entire range of body sizes due to differences in the developmental trajectories of individuals and species. Using data from birds captured in continuous and fragmented habitats in Brazil and Colombia we examined the bivariate distribution of body mass and tarsus length. We found distinctive aggregates of points represented by individuals with similar body masses and tarsus lengths. Power functions fitted to aggregations of data points explained a larger percent of the variance than that fitted to all the data. These power functions exhibited different scaling coefficients and exponents. Bivariate plots of body mass and tarsus length for continuous and fragmented forests exhibited some important differences indicating that certain bird morphologies are affected by forest fragmentation. Complex allometries described best these data, indicating that multimodality in body size in animal assemblages may arise through mechanisms involving the development of organisms.

KEY WORDS: multimodal distributions, body size, neotropical fragmented habitats, birds, complex allometries