Module 11 - Speed of Speciation

    I like the Biological species concept definition of speciation in which speciation occurs if reproduction isolation occurs. Of course, researchers can base it off of standards from morphology, phylogeny, genetics, ecology, etc, but they do not acknowledge species as true natural entities as the biological species concept does. Species are concretely different organisms, not just a designated boundary made by man. 
    Factors such as gene flow, genetic drift, mutation, selection, and geographical isolation greatly impact speciation - whether it occurs, the rate of speciation, if the different species can re-combine, so to speak. Not all of these factors have to be present. Divergence and speciation can occur without selection. Mutations in a population can be fixed via genetic drift, but then the different evolving species can come back together through hybridization. Or, there may be enough significant incompatibilities that they cannot hybridize or their offspring are sterile. Speciation is a constant process. Only until definite reproduction isolation is met is it finalized. The actual amount of time that it takes for speciation to occur also depends on the organism, especially the time between generations. It could be one generation or many generations. How strong selection in their environment is and how quickly their environment changes is also a factor. 
    In allopatric speciation, speciation arrises due to physical separation, but non-allopatric speciation can occur in which new species appear without physical separation. The two different species just adapt to the environment in two different ways. Maybe there is an environment with plenty of bugs and flowers. Two species of birds from a common ancestor can develop - one drinking the nectar of the flowers and one consuming the insects/bees, what have you. They both have the same resources provided, but a mutation in one or the other has led to selection and preference for the utilization of one over the other. When these two birds meet, they may not recognize each other as potential mates due to their appearance (which could have changed in adapting to their specific food source) or their behaviors. This could be classified as pre-mating isolation or perhaps behavioral isolation. There are other types of isolation as well. Mechanical isolation is when species have evolved different genitalia, so they physically cannot reproduce. Post-mating, pre-zygotic isolation occurs in when the species can mate, and possibly do, but their gametes cannot fuse to form a viable egg. Post-zygotic isolation occurs when the hybrid offspring are unable to, themselves, reproduce or are not well adapted to live in their environment as their parents were. 

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