| barriers to sympatry between avian sibling species (paridae: baeolophus) in local secondary contact. | range limits and secondary contact zones often occur at ecotones between major associations of habitat and climate. therefore, understanding processes that limit sympatry between species in such areas provides an important framework for testing biogeographic and evolutionary hypotheses. theoretical and empirical work has shown that the evolution of species borders is influenced by a complexity of factors, including gene flow from central to peripheral populations and the ability of species to ad ... | 2004 | 15341159 |