The alternative mating strategies of male topi, Damaliscus lunatus

Abstract

Form and flexibility of the mating strategies of male topi ( Damaliscus lunatus) appear to be adaptations to patterns of movement by females and their grouping behaviour and to competition with other males for access to females. Most males defend resource territories, but the size and structure of those territories are highly variable. In the productive and homogeneous grass swards where large concentrations of topi congregate in the wet season, intrasexual competition is intense and territories usually measure < 0.2 km 2. Where the sward is very heterogeneous, females occur in small groups because the best food for each season is available only in small amounts. Here, male intrasexual competition is less intense and males defend territories of up to 2 or 3 km 2. In the homogeneous areas, female ranges include many small male territories; in the areas of heterogeneous grassland, some females remain within single male territories. There is continuous variation between these extremes. Under local conditions where large, mobile groups of females exist, some males abandon resource defence and instead move with the females and attempt to monopolise a small part of the group covering some 0.6 ha. There are also static resource territories in the same areas. Further work is needed to clarify the circumstances under which these alternatives are adopted. Males which join leks defend very small territories, sometimes < 0.1 ha, containing negligible food resources. Lekking appears to be a response to the concentrations of females which collect in open, raised areas at resting time. One reason for this aggregation may be to avoid the risk of predation by lions ( Panthera leo) in long-grass feeding areas. Mating success is very uneven on leks: a few males achieve most matings. In spite of this, lekking is a very costly strategy for all males, with more time spent in contests and a higher risk of injury, than would occur in resource territories. Unsuccessful males on leks incur high costs but achieve low benefits. Such males stay on leks because, being smaller than males in resource territories, they may be unable to win resource territories by fighting. Small males adopt a “satellite” strategy, trying to intercept females as they move towards successful territories. In this way, they may achieve a low level of mating success. Leks may arise when small males cluster around a few, larger, resource males which are exceptionally successful because their territories contain part of an area where females congregate for anti-predator advantage.