OPUS: The Biotic Challenge Hypothesis, an Eco-evolutionary Mechanism for Tropical Diversity

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The staggering diversity of tropical organisms and their species interactions have inhibited generalizations about how this diversity arose and how species coexist. Generalizations based on simple communities and ecological models fail to scale-up adequately to encompass the most species-rich terrestrial assemblages, especially those in the New World tropics (Neotropics). Review of the vast diversity of traits among neotropical insect-feeding birds and their prey inspired the Biotic Challenge Hypothesis, which asserts that as tropical habitats accumulated diverse species over tens of millions of years, intense competition and predation necessitated the evolution of many unique and specialized adaptations. How this process might have increased the evolution of new traits and species, and also the fragility of tropical systems, is inadequately articulated. This project posits that interactions among species, especially predation and competition for resources are essential to understanding the evolution of hyper-diverse tropical communities and current threats. A key broader impact of this project will be to explore why tropical species are so sensitive to global change threats and thus require more effective conservation and management strategies. Other broader impacts include the creation and dissemination of a publicly available database, training students with diverse backgrounds, and production of materials for a range of audiences. The Biotic Challenge Hypothesis integrates two evolutionary species interactions, coevolutionary arms races between predators and their prey, and diffuse competition involving dozens of often phylogenetically unrelated species. These interactions necessitated feeding specializations to find, subdue, and process prey; and energetically conservative physiologies. A tradeoff (cost) of these specializations is poor dispersal ability, augmenting both geographic differentiation within species and speciation rate, the latter positively reinforcing tropical species diversity. This project will explore in detail how the dynamic interactions among predators, prey, and competitors has driven diversification in many animal and plant assemblages, including birds and their insect prey, tropical plants and their enemies, and plant-animal mutualisms. The most important broader impact is a book that elaborates the causes and consequences of the Biotic Challenge Hypothesis, especially as it relates to the evolution of ecological specialization and poor dispersal. Both of these outcomes exacerbate the sensitivity of tropical species to many global change impacts including declining insect populations. Other broader impacts include training an undergraduate and an early graduate student to produce a database of avian prey data, on which many inferences in the book are based; and disseminating the findings and concepts to broad audiences.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.