Breeding systems, habitat overlap, and activity patterns of monogamous and promiscuous mating in Peromyscus californicus and P. boylii

The purpose of my study was to use the comparative approach to compare and contrast the behaviour of the monogamous California mouse (Peromyscus californicus) and the brush mouse (P. boylii), of previously unknown breeding system. I used trap associations, nest-site use, a food-selection experiment, and measurements of nightly activity, to describe resource partitioning by syntopic P. californicus and P. boylii. Peromyscus boylii was frequently caught near live oak (Quercus agrifolia), nested under canopies with high densities of Q. agrifolia, and had a diet preference for Q. agrifolia acorns. Relative to P. boylii, P. californicus was a habitat generalist that had a broad diet and did not discriminate among canopy plants for nest-sites. At high densities of P. californicus, interspecific interactions likely maintain separation between the two species.;I characterized the breeding system of Peromyscus boylii by describing spacing behaviour, mating interaction, nest co-occupancy, and litter paternity characteristics. Adult sex ratio was near equal in 1997 and biased towards females in 1998 when population density was high relative to 1997. In both years, males and females did not differ in home range size, but inter- and intra-sexual home-range overlap was higher in 1998 than 1997. Males and females did not share nests and did not maintain long-term pair-bonds. The probability of a resident male mating was less than 0.50 during both years, and some non-resident males mated with resident females. Approximately 80% of resident males never mated whereas 20% mated at least once and 2% mated more than once. Although multiple matings appeared infrequent based on behavioural observations, microsatellite analysis of litters showed that 4 of 7 litters were sired by more than one male. Along the traditional continuum of mammalian mating systems, the mating system of P. boylii is best characterized as promiscuous.;Having established that (1) interspecific interactions and habitat partitioning facilitates the coexistence of P. boylii and P. californicus, and, that, (2) the mating system of P. boylii is best characterized as promiscuous, I tested specific predictions about behavioural strategies associated with monogamous and promiscuous breeding systems. Departure times from nests differed between species. I found differences in total time of nightly activity for males and females of both species consistent with differences in body size, energetic costs of reproduction, and behavioural strategies associated with monogamy and promiscuity. The larger P. californicus tended towards more total time active than the smaller P. boylii, and in general, females of both species spent more total time active than males. However, in the year with a relatively low density of female P. boylii (1997), male P. boylii were as active as females, presumably to meet activity requirements of searching, pursuing, and guarding mates. The range of nocturnal activity and the return time from nocturnal activity were remarkably similar among males and females of both species. Although there were year differences in factors associated with how the total time spent active was partitioned, within each year the total bout number, bout length, and minimum and maximum bouts were similar among males and females of both species. There was a pattern for lactating females to spend more time active than pregnant females. My result suggests that regardless of breeding system, there is a basic activity schedule for both species of Peromyscus and that the energy requirements for males and females are comparable.