UCLA

Competition among species, whether mediated through shared resources or direct behavioral interactions, has significant evolutionary effects. Ecological and agonistic character displacement (ECD and ACD) are processes by which competition drives evolutionary shifts in resource use and interspecific aggression, respectively. Recent contact zones provide opportunities to study these processes. In Chapters 1-3, we used the invasion of Florida by two lizards, Anolis sagrei and A. cristatellus, to investigate the role of interspecific competition in their evolution. First, we asked whether ECD has occurred in these species. We measured morphology and bite force in sympatric and allopatric populations, and found that A. cristatellus had a more robust head and greater bite force in sympatry. This shift results in phenotypic divergence, consistent with ECD. Next, we asked whether interspecific fights have driven shifts in aggressive behavior through ACD. We found that male A. sagrei were less aggressive toward heterospecifics in sympatry than in allopatry, while male A. cristatellus were behaviorally dominant. A. sagrei's reduced heterospecific aggression in sympatry may represent an adaptation to avoid fights with A. cristatellus. Finally, the effects of competition depend on its intensity, so we used a species-removal experiment to ask whether A. sagrei and A. cristatellus were competing in South Miami. While the two species' habitat use differed significantly, the removals did not influence their habitat use, movements, or body condition. In summary, the morphology and behavior of A. sagrei and A. cristatellus suggest that competition may have influenced their evolution, but we found little evidence of contemporary competition between them. In Chapter 4, we present a comparative analysis of the ecological and evolutionary factors underlying interspecific territoriality (IT) in North American warblers (Parulidae). We searched the literature for records of IT and compared species that exhibited IT with species that did not. Over half of North American parulids showed IT. Species exhibiting IT were more similar to one another in morphology, feeding guild, and habitat than expected by chance, but phylogenetic relatedness was a better predictor of IT than any of these factors, highlighting the role that evolutionary history plays in current ecological interactions.