Changes in Patterns of Territory and Habitat Overlap in Wood-Warblers Over Evolutionary Time

Abstract

Patterns of community assembly among organisms are highly influenced by the ecological traits and strategies of the species that make up those communities. The conservation of ancestral traits can be important in determining how closely related species partition space and habitat on a local scale. Shared ecological traits and strategies of closely related species suggest that they should overlap in space and use similar habitats. However, ecological similarity may result in fitness costs when closely related species live together. Previous work on birds suggests that close relatives avoid each other by using different habitats. I used the radiation of Dendroica wood-warblers to test these two alternative hypotheses and determine how closely related species partition space and habitat, and how patterns of spatial overlap and habitat use change over evolutionary timescales. I measured territory and habitat overlap among nine sympatric species of Dendroica, Setophaga and Mniotila to determine how time since common ancestry is related to patterns of spatial overlap and habitat use at the Queen's University Biological Station in eastern Ontario. I predicted that closely related species would separate by habitat and not overlap their territories. However, I found that the two most recently diverged species pairs overlap their territories and habitats significantly more than do pairs of more distantly divergent species. This pattern contrasts with previous studies on wood-warblers and the ecologically similar Phylloscopus leaf-warblers. These results suggest that during allopatric speciation Dendroica species do not differentiate in habitat on a local scale; rather, habitat differentiation occurs after closely related species have returned to sympatry.