Ecology and the origin of species

The ecological hypothesis of speciation is that reproductive isolation evol ves ultimately as a consequence of divergent natural selection on traits be tween environments. Ecological speciation is general and might occur in all opatry or sympatry. involve many agents of natural selection, and result fr om a combination of adaptive processes. The main difficulty of the ecologic al hypothesis has been the scarcity of examples from nature, but several po tential cases have recently emerged. I review the mechanisms that give rise to new species by divergent selection, compare ecological speciation with its alternatives, summarize recent tests in nature, and highlight areas req uiring research.