Contest versus scramble competition for mates: The composition and spatialstructure of a population of gray mouse lemurs (Microcebus murinus) in north-west Madagascar

The modes of intrasexual competition interacting in many dispersed societie s of nocturnal solitary foragers are still poorly understood. In this study we investigate the spatial structure within a free-living population of gr ay mouse lemurs (Microcebus murinus) in order to test for the first time th e predictions from two contrasting models of male intrasexual competition o n the population level. The contest competition model predicts an uneven di stribution of the sexes in a population nucleus with a female biased sex ra tio in the center and a male biased sex ratio in the periphery. In contrast the scramble competition model predicts males and females being distribute d evenly throughout their habitat with a constant sex ratio. Nine capture/r ecapture periods within three consecutive mating seasons revealed a continu ous male biased sex ratio in the adult population with even trapping rates for the sexes. The male biased sex ratio could either be explained with pos tnatal female biased mortality or with a male biased natal sex ratio. This male biased sex ratio was apparent in all parts of the study site, indicati ng that the population was not subdivided into a female biased core and a m ale biased periphery, Furthermore, the majority of adult males have been ca ptured at the same site as or in vicinity to females. Consequently, a large proportion of males had spatial access to females during the mating season . No signs of monopolization of females by certain dominant males could be detected. These data support the predictions from the scramble competition model and the concept of a promiscuous mating system for this species.