Spacing pattern, intersexual competition and niche segregation in American mink

Many animals, especially mustelids, show a spacing pattern known as intrasexual territoriality in which territorial animals defend areas against individuals of the same sex and there is extensive overlap between sexes. It has been argued that this overlap leads to sharing of food resources between territorial individuals of different sexes which has a net cost for territorial individuals. Several mechanisms have been proposed to reduce competition between sexes, many of them derived from sexual dimorphism, which is closely related to intrasexual territoriality. Among the suggested mechanism is spatial segregation between animals with overlapping areas, although it remains largely untested. We hypothesized that sexual spatial segregation in mustelids could be a consequence of a niche partition in habitat between sexes due to different optimums. We conducted a fine-grained radio tracking survey of seven feral American minks in winter. We compared home ranges, relative spatial positions and characteristics of radio-locations of different sexes. We also considered relative distances between simultaneous locations of overlapping individuals to test for dynamic territorial interactions. There were differences in the home range composition of males and females, and in their relative spatial location, proving spatial segregation between sexes. The comparison of locations showed that females preferred smaller streams as opposed to males that preferred large streams. In addition relative spatial position of female locations was independent of location of males in overlapping pairs, suggesting niche segregation caused by different sexual habitat preferences. Sexual habitat segregation is discussed as a powerful means of avoiding intersexual competition in species exhibiting intrasexual territoriality as a spacing pattern.