Ecological Assembly of Leaf-Litter Anuran Communities Across a Neotropical Land-Bridge Archipelago

Abstract

The conspicuous variation in time and space of richness and composition of biological communities has intrigued ecologists for decades. In this dissertation, I explore the patterns and ecological mechanisms that underlie the community assembly of leaf-litter anurans on a Neotropical archipelago. I combined experimental and observational approaches to: first, identify patterns of body size variation in leaf-litter anurans; second, assess how coloration and body size variation in a territorial and common species, Oophaga pumilio, associates with aggressiveness and dominance, and how this association influences the outcome of species interactions; and third, examine species co-occurrence and body size overlap patterns, assessing how differences in coloration - associated with aggressive behavior in O. pumilio - influence the assembly of leaf-litter anuran communities. In the first chapter of this dissertation, I present evidence for consistent insular reductions in body size in only one species, Oophaga pumilio. Size reductions in this small species do not fit with predictions of the “Island Rule” – the trend towards insular gigantism in small species, and dwarfism in large species – contrasting with previous findings on other vertebrates. In the second chapter, I provide support for a positive relationship between the strength of anti-predator coloration, agonistic behavior, and dominance in interspecific, intraguild interactions. Resident frogs from more conspicuous, red-colored O. pumilio populations were more aggressive towards same-morph conspecifics and one heterospecific than less-conspicuous green-colored populations, dominating most interactions. In the third chapter, I provide evidence for the role that intraspecific phenotypic variation plays in the assembly of communities, and illustrate how both deterministic and neutral processes may simultaneously contribute to the assembly of animal communities. I found little evidence for morphological segregation at local scales, and random species co-occurrence patterns at local and regional scales for the entire assemblage. Segregated patterns emerged at the regional scale for sub-matrices that included islands where highly conspicuous, and highly dominant morphs of O. pumilio exclusively occurred. Overall, findings from this dissertation provide evidence for the important role that intraspecific phenotypic variation plays in the assembly of animal communities and illustrate how different mechanisms may underlie the structure of biological communities at multiple scales.