Indirect measures of reproductive effort in a resource-defense polygynous ungulate: Territorial defense by male guanacos

Abstract

Trade-offs between reproductive effort and activities that are likely to enhance survival have been studied extensively in harem defense ungulates. However, among resource defense systems, ecological determinants of the variation in male reproductive effort are less understood. The aim of this study was to assess the extent of the effort devoted to territorial defense by male guanacos and how this is affected by predation risk. Time allocation to different activities and displays of aggressive behavior were compared between territorial and bachelor male guanacos within two populations with contrasting levels of predation risk. Territorial males devoted almost twice the time than bachelors to vigilance and moving, at the expense of foraging time. Aggressive interactions were more frequent and severe for territorial males than for bachelors, based on observation. These differences were larger during the reproductive season but remained statistically significant after this period, highlighting the extended effort towards territorial defense beyond the peak of reproductive activity. In contrast to previous observations on females of the same populations, there was no effect of predation risk level or group size on male time allocation, suggesting that under the ecological conditions of the study, intra-sexual competition entails a stronger influence on male individual behavior than predation risk level.