Sexual adaptations to high density in hermaphrodites

Hermaphrodites are generally seen as species adapted to conditions of low m ate availability. This is primarily because hermaphrodites can adjust alloc ation of resources to each sex function in response to current conditions, making reproduction more efficient. Adaptation to low density is further en hanced because many have the ability to self-fertilize and because the enco unter rate of potential mates is twice as high for a hermaphroditic than fo r a gonochoric species. Yet, many hermaphrodites often occur at consistentl y high densities. Herein I review the consequences of high density on herma phrodite sexual behaviour and show that this approach can explain the prese nce of a number of obvious adaptations known from hermaphrodites. These ada ptations cannot be explained by assuming that low density has been the rule in their evolutionary past.