Reinforcement of Reproductive Isolation: Plants Versus Animals

Selection for reproductive isolation may be stimulated by the loss of reproductive potential associated with heterospecific mating or by competition for a resource upon which mating success rests. It is proposed that such selection in response to heterospecific mating is more likely to occur in animals (insects and vertebrates) than in plants (angiosperms) because animals generally experience a greater reproductive handicap per breeding episode. It is also proposed that selection for reproductive isolation in response to competition is more likely to occur in animal-pollinated plants than in animals, because plants, unlike animals, are dependent upon a specific resource (the pollinators). These relationships lead to the inference that selection for reproductive isolation in plants will usually be the product of competition, whereas in animals it will usually be the product of heterospecific mating.