Territoriality and reproductive interference between species

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Why do some closely related species coexist peacefully while others fight over space? Aggressive territorial interactions between species are very common, much more so than expected based on current theory, and may determine whether species are able to coexist. The importance of understanding the causes of such costly interactions is highlighted by evidence that the ranges of many species are changing rapidly. One potentially crucial factor that has generally been overlooked is reproductive interference. Reproductive interference occurs when a male or a female of a species recognizes a male or female of a different species as a potential mate. This mistake has negative impacts on the fitness of both species. Reproductive interference is effectively a form of mate competition and thus may be the root cause of territorial aggression between species in some cases. By developing new theory and testing it with new empirical research on dragonflies and birds, this project will advance our understanding of why aggression between species is so prevalent.This research aims to clarify the factors that determine whether interspecific territoriality is evolutionarily stable or transitory. An individual-based modeling framework that the researchers have developed for studying the consequences of secondary contact between closely related species will be extended to evaluate the consequences of reproductive interference between (1) species in which males defend mating territories, and (2) species in which males defend multi-purpose territories. Rubyspot (Hetaerina spp.) damselflies are the ideal study system for testing the first of these new models. It has already been established that interspecific territoriality covaries with reproductive interference in this genus, but further research is needed to determine whether the variation in reproductive interference explains the variation in interspecific aggression. Fieldwork will be carried out to parameterize the model and to test its predictions on 10 species pairs. The second model, for species that defend multi-purpose territories, will be based on the biology of socially monogamous passerine birds, and parameterized using data from the literature, to evaluate whether current levels of resource competition are sufficient to maintain interspecific territoriality in the absence of reproductive interference. Finally, a major comparative study of North American passerine birds will be carried out to elucidate the ecological, phenotypic and phylogenetic correlates of interspecific territoriality. This work includes substantial international fieldwork experiences for students in Costa Rica and Mexico and is partially funded through the Global Venture Fund.