Ecological speciation

Ecological speciation is the process by which ecologically based divergent selection between different environments leads to the creation of reproductive barriers between populations. This is often the result of selection over traits which are genetically correlated to reproductive isolation, thus speciation occurs as a by-product of adaptive divergence.

Ecological selection is "the interaction of individuals with their environment during resource acquisition". Natural selection is inherently involved in the process of speciation, whereby, "under ecological speciation, populations in different environments, or populations exploiting different resources, experience contrasting natural selection pressures on the traits that directly or indirectly bring about the evolution of reproductive isolation". Evidence for the role ecology plays in the process of speciation exists. Studies of stickleback populations support ecologically-linked speciation arising as a by-product, alongside numerous studies of parallel speciation—of which, substantiates speciation's occurrence in nature.

The key difference between ecological speciation and other kinds of speciation, is that it is triggered by divergent natural selection among different habitats, as opposed to other kinds of speciation processes, like random genetic drift, the fixation of incompatible mutations in populations experiencing similar selective pressures, or various forms of sexual selection not involving selection on ecologically relevant traits. Ecological speciation can occur either in allopatry, sympatry, or parapatry. The only requirement being that speciation occurs as a result of adaptation to different ecological or micro-ecological conditions.

Some debate exists over the framework concerning the delineation of whether a speciation event is ecological or nonecological. "The pervasive effect of selection suggests that adaptive evolution and speciation are inseparable, casting doubt on whether speciation is ever nonecological".

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