IB Biology Sub-topic A4.1 Notes

At this point, you have heard of reproductive isolation leading to speciation a few times. You need to understand that the type of isolation influences the type of speciation:

1. Allopatric speciation - this is speciation that occurs due to geographical isolation. An example would be the Darwinian finches, spread across multiple islands. Interestingly, this therefore creates multiple gene pools for a single species.
2. Sympatric speciation - this is speciation that occurs due to temporal or behavioural isolation. An example would be apple flies, where the hawthorn and non-hawthorn varieties only mate in specific types of apples, despite living in the same area.

The type of isolation influences how and how long speciation occurs for, but eventually the two populations evolve to exhibit different characteristics. Over a sufficient time period, the two populations cannot interbreed to produce fertile offspring, and are thus classed as two different species.