Foraging competition in larger groups overrides harassment avoidance benefits in female reindeer (Rangifer tarandus)
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Male harassment toward females during the breeding season may have a negative effect on their reproductive success by disturbing their foraging activity, thereby inducing somatic costs. Accordingly, it is predicted that females will choose mates based on their ability to provide protection or will aggregate into large groups to dilute per capita harassment level. Conversely, increasing group size may also lead to a decrease in foraging activity by increasing foraging competition, but this effect has rarely been considered in mating tactic studies. This study examined the importance of two non-exclusive hypotheses in explaining the variations of the female activity budget during the breeding season: the male harassment hypothesis, and the female foraging competition hypothesis. We used focal observations of female activity from known mating groups collected during the breeding season from a long-term (15 years) study on reindeer Rangifer tarandus. We found that females were more disturbed (i.e., spent less time feeding) in the presence of young dominant males, and marginally disturbed in the presence of satellite males, which supports the male harassment hypothesis. We also found that female disturbance level increased with group size, being independent of the adult sex ratio. Consequently, these results rejected the dilution effect, but strongly supported the foraging competition hypothesis. This study therefore highlights a potential conflict in female behaviour. Indeed, any gains from harassment protection were negated by an increase of 6–7 females, since adult males lead larger groups than young males.
KeywordsMating tactic Ungulate Group dynamics Reindeer Sexual selection
The authors thank Mika Tervonen of the Finnish Reindeer Herder’s Association for the management of Reindeer in Finland, and Heikki Törmänen of the Reindeer Research Station for compiling this long-term database. We thank Hallvard Gjøstein, Eliana Pintus, Sacha Engelhardt and numerous field crew members who helped with data collection over the years, and Juan Carranza, Denis Réale and two anonymous reviewers for comments. Handling of animals and data collection was done in agreement with the Animal Ethics and Care certificate provided by Concordia University (AREC-2010-WELA and AREC-2011-WELA) and by the Finnish National Advisory Board on Research Ethics.
Author contribution statement
GB, RBW, ØH and MN conceived and designed the experiments. SU, GB, RBW, ØH performed the experiments. SU, GB analyzed the data. SU, GB, RBW wrote the manuscript. ØH, MN provided editorial advices.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
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