A burst of
speciation in
Setophaga occurred between 4.5 and 7 million years ago. This time frame roughly corresponds to the transition from the
Miocene to the
Pliocene period, when an abrupt rise in temperature and the fragmentation of forest habitats in North America may have caused
allopatric speciation in the genus. It is widely agreed that this speciation constitutes an
adaptive radiation, though recent evidence is mixed, noting that evidence of both adaptive and non-adaptive radiations exists. Up to several
Setophaga species coexist in regions such as northeastern North America. Since these species are strikingly similar in both diet and
morphology, this was once thought to be a violation of the laws of
evolution. Further study concluded that species coexist through subtle feeding differences due to
niche partitioning and diffuse exploitative
interspecific competition: rather than compete directly for the same food resources, species utilize slightly different feeding strategies to capture a slightly different set of prey species. == List of species ==