Male space use and mating strategies in relation to the spatial distribution of females in bank voles (Myodes glareolus)

Bacheloroppgave i utmarksforvaltning. Evenstad 2011

The spatial and temporal distribution of females is affected by the distribution of food and other resources such as nest sites, whereas spacing behavior of males is suggested to be determined by the distribution of females. When females are aggregated, the males should display territorial behavior in order to monopolize this defensible resource, while territorial, more dispersed females should lead males to have large, overlapping home ranges. However, previous studies found contrasting results. In the present study, we thus investigated how males’ space use and mating strategies are affected by females’ distribution in bank vole Myodes glareolus. We manipulated the distribution and predictability of food in order to influence the spatial distribution of females: the food was either dispersed (treatment “spread”), spatially clumped and predictable (treatment “fixed”), or spatially clumped but unpredictable (treatment “unpredictable”). This food manipulation successfully generated different spatial distribution of females, and we investigated (i) space use patterns in males, estimated from trapping data, and (ii) their mating and reproductive success through paternity analyses. Our results showed that males’ home range size and overlap did not differ between the treatments, but they decreased through time, likely because of the increasing overall density. The weight of males had an effect on their reproductive success (number of offspring), but the distribution of females did not. The weight also had an effect on the mating success (number of partners), in interaction with the treatment. In both Fixed and Unpredictable treatments, the number of partners increased with the weight of males, but in the Spread treatments there was not such a relationship. In the Fixed and Unpredictable treatments, males might have been organized in social hierarchies, with bigger, dominant males having more chances to get partners and offspring. Further research is needed to investigate dominance relationships among males, and to test whether having a greater body mass benefit individuals during direct aggressive conflicts, or during sperm competition.