Coexistence Maintained by Sexual Interactions

Recent empirical studies have uncovered the coexistence of cryptic species that are morphologically indistinguishable yet genetically different. As they lack known ecological differentiation between them, it has been suggested that species-specific sexual interactions may be able to stabilize their coexistence. We investigated two types of such interactions: (1) traumatic mating suffered by females and (2) interference competition among males. We have learned that the consequences of the two types of sexual interactions are markedly different. Traumatic mating may affect the fertility and/or survival of females. In both cases it introduces negative density dependence and, alone, can regulate the growth of a single population. Also, traumatic mating is able to stabilize the coexistence of ecologically equivalent populations, provided that it is stronger within species than between them. In contrast, male competition cannot constrain population growth without density dependence of a different origin. Accordingly, it destabilizes, rather than stabilizes, neutral coexistence of ecologically equivalent species. A targeted, species-specific study of traumatic mating suffered by females would provide empirical support for the diversity-maintaining role of sexual interactions.