Courtesy of Victoria Braithwaite
Ecological niche separation causes threespine stickleback populations to develop choosy mating preferences.
Evolutionary biologists, both theoreticians and empiricists, have argued for decades about the relative merits of two speciation scenarios: allopatry and sympatry. The multifaceted debate bristles with any number of sharply contested points, but one that has provoked the greatest polarization is the concept of reinforcement. This is the crucial last step in the process, when behavioral mechanisms finally become established, driving a reproductive wedge between incipient species.
Broad consensus has been reached on what constitutes a "good" biological species. The late Ernst Mayr defined species as "groups of interbreeding natural populations that are reproductively isolated from other such groups."1 Nevertheless, at that critical point when one species becomes two, the distinction often becomes blurred. The whole theory of evolution rests on the notion that species can split and diverge, but the precise mechanics of ...
