(1) How important are closely related species to local diversity? A global test — Closely related species are thought to share many ecological traits and preferences in common, and thus compete for resources within local communities. Despite these costs of competition, recent work suggests that closely related species make up an important component of local diversity, and that their ability to live together may constrain broader patterns of diversification over time. The goal of this project is to document the importance of closely related species to local communities of birds and test the idea that this importance varies with latitude. The work would require compilation of species lists for natural parks and preserves from around the world, beginning with the Americas. Initial tests would involve a taxonomic definition of closely related species (congeners); additional tests could use a global phylogeny of birds to defines relatedness by the time since they shared a common ancestor.

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(2) Do behaviourally subordinate species have greater ecological breadth? — In 1974, Douglas Morse (American Naturalist) described a repeated pattern of socially dominant and subordinate species segregating along environmental gradients. When the dominant species was removed, the subordinate expanded its distribution, suggesting that subordinate species had greater ecological breadth – they were adapted to their own distribution and resources, and to those of the dominant species as well. To date, only one study has independently tested this hypothesis (Freshwater et al. 2014, Ecology) and, surprisingly, found no difference between the ecological breadths of closely related dominant and subordinate species of birds (examining diet, foraging behaviour, nest sites, and habitat). This test, however, examined ecological breadth in locations where dominant and subordinate species co-occurred, and thus dominant species could have restricted the use of resources and habitats of the subordinate species. This proposed project would extend the work of Freshwater et al. (2014) to examine the ecological breadth of closely related dominant and subordinate species in areas of sympatry and allopatry, allowing a direct comparison of ecological breadth in areas with and without dominant species. The work would provide one of the few direct tests of Morse's hypothesis, and will further our understanding of how important ecological traits covary with the position of species within a social dominance hierarchy.

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(3) What ecological traits covary with behavioural dominance of species? — Previous work in our lab (Freshwater et al. 2014, Ecology) was the first to describe repeated patterns of trait divergence that depended upon the position of a species within a social dominance hierarchy. Specifically, subordinate species of birds arrived earlier on their breeding sites, initiated breeding earlier, had lower annual adult survivorship, laid larger eggs for their weight, and migrated greater distances, than closely related, dominant species. These patterns were exciting because they suggested that important traits related to phenology, life history, and migration are influenced by where a species sits within a social hierarchy of other species. The work was based on an analysis of 65 closely related species pairs of North American birds – all of the data on dominance interactions among congeners that was available at the time. Today, we have dominance data for ~200 species pairs of birds from around the world. Are the patterns of trait divergence evident in North American dominance hierarchies representative of birds from around the world? Are other patterns of trait divergence (e.g., geographic range size, distribution) evident among dominant and subordinate species when addressed with a larger sample? This project would revisit some of the questions addressed by Freshwater et al. (2014) using a larger, more powerful, global dataset on dominance relationships among birds.

 

(4) Behavioural dominance interactions among species for a shared resource under varying levels of resource availability — Aggressive interactions among species for a shared resource are common in nature and typically asymmetric, with a socially dominant and subordinate species. These behavioural dominance interactions determine which species has priority access to shared resources, but we expect the intensity and outcome of such interactions to vary as a function of resource availability. For example, as resources become scarce, interactions may become more intense and the dominant species may monopolize the rare resource; when resources are common, the dominant species may be less aggressive towards subordinates who present a reduced risk to the dominant's acquisition of resources. In this project, we will test these ideas using hummingbird interactions at nectar feeders in a hyper-diverse hummingbird community in the Andes of Ecuador. Using live-stream video, we will measure the frequency and outcome of interactions at feeders at different levels of resource availability.

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