An example is mating horses and donkeys to get mules. Sometimes reproductive isolation is incomplete and contact is reestablished before many genetic differences have accumulated. Then there is successful interbreeding and no new species forms. Hybrid zone - where two populations come into contact and interbreed. Life history traits influence speciation rates.
Heterogeneous environments favor high speciation rates.
Short generation times enhance speciation. Shorter generation times result in more generations per unit time and generate the potential for more evolutionary changes per unit time.