title: Between-gender differences in vigilance do not necessarily lead to differences in foraging-vigilance tradeoffs.
abstract: When prey are time limited in their access to food, any trade-off involving time should ultimately affect their intake rate. In many herbivores, males and females experience different ecological pressures affecting their survival and reproduction because of differences in morphology, physiology and energy/nutrient requirements. If males and females have different vigilance strategies that affect their intake rates differently, they will suffer different foraging costs. This is particularly relevant in sexually monomorphic herbivores, where the two sexes have similar basal energy/nutrient requirements and risk of predation. We investigated how gender, reproductive status, age, group size, predation risk, and food biomass affected vigilance, intake rate, and their trade-off in a monomorphic species, the plains zebra (Equus quagga). Males were more vigilant than females, and lactating females were less vigilant than other females; the levels of vigilance were low (ca. 10 % of feeding time). The effects on time spent feeding, bite rates and intake rates were small and statistically not significant. Reproductive status did not affect the strength of the relationship between vigilance and intake rate, but intake rates increased with group size and, for adult females, were higher in tall grass. While gender and reproductive status were major drivers of vigilance, and group size and food biomass of the rate of food intake, males and females adjust their bite rates and food intake with vigilance in similar ways. Our results support the hypothesis that in monomorphic animals, males and females seem to make similar trade-offs (i.e. adjustments) between vigilance and intake rate.
authors.affiliation: Centre d'Etudes Biologiques de Chizé, UMR-CNRS 7372, Université de la Rochelle, Beauvoir-Sur-Niort, France.
authors.forename: Florian
authors.initials: F
authors.lastname: Barnier
authors.affiliation: Centre d'Etudes Biologiques de Chizé, UMR-CNRS 7372, Université de la Rochelle, Beauvoir-Sur-Niort, France.
authors.forename: Patrick
authors.initials: P
authors.lastname: Duncan
authors.affiliation: Laboratoire de Biométrie et Biologie Evolutive, UMR-CNRS 5558, Université Claude Bernard Lyon 1, Lyon, Villeurbanne, France.
authors.forename: Hervé
authors.initials: H
authors.lastname: Fritz
authors.affiliation: Laboratoire Evolution et Diversité Biologique, CNRS, ENFA, UMR 5174, Université de Toulouse, Toulouse, France.
authors.forename: Pierrick
authors.initials: P
authors.lastname: Blanchard
authors.affiliation: Department of Ecology and Evolutionary Biology, Princeton University, Princeton, NJ, USA.
authors.forename: Daniel I
authors.initials: DI
authors.lastname: Rubenstein
authors.affiliation: LETG-Angers, UMR 6554 CNRS, Université d'Angers, Campus Belle Beille, 2 Boulevard Lavoisier, 49045, Angers, France. olivier.pays@univ-angers.fr.
authors.forename: Olivier
authors.initials: O
authors.lastname: Pays
mesh_terms: D000818:Animals; D005260:Female; D060434:Herbivory; D007774:Lactation; D008297:Male; D011235:Predatory Behavior; D012098:Reproduction; D012727:Sex Characteristics
keywords: Anti-predator behaviour; Gender effect; Herbivores; Intake rate; Zebra