Habitat Isolation: often a direct byproduct of adaptation to the environment. Seems based on relatively few genes. “Habitat” can include host preference in addition to soil type preference and other habitats.
Pollinator Isolation: gene flow between flowering plants is reduced if the species use different pollinators. Strong dependence on a particular pollinator can limit flowers to the range of that pollinator. It’s produced largely by differences in flower color and nectar volume. Perhaps a small number of genes with large effects?
Temporal Isolation: gene flow is impeded due to different breeding times between species. “Some species of periodical cicada breed simultaneously only every two centuries” — Woah! That’s pretty interesting.
Diverse biological bases of temporal isolation: different responses to same environmental cue, different responses to different cues, or pleiotrophic byproduct of habitat differences (flowering time dependent on soil moisture). Temporal isolation can be completely non-genetic (offyear breeders can be produced by environmental or developmental accidents), and is the only isolating barrier that can cause sympatric speciation. Current studies suggest, however, that temporal isolation is not that important in animals. This raises more questions in my mind about the plausibility of sympatric speciation. Some do suggest that temporal isolation is more important in plants. Perhaps it simply happens post-speciation?
On a somewhat related note, reading this book made explaining speciation to the Intro Zoo (ZOO 1114) students I tutor a lot easier. Speciation is a difficult concept to grasp for many of them.
However, I do not think I will take much of an interest in this area in the future. The book is informative, but reading it makes me quite sleepy… The authors do suggest that (if one is interested) there is a fairly pressing need for more study.
Science would be a lot easier with a time machine or two.
