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Effect of the nutritional environment and reproductive investment on herbivore-parasite interactions in grazing environments

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Publication details

JournalBehavioral Ecology
DateE-pub ahead of print - 28 Apr 2006
DatePublished (current) - Jul 2006
Issue number4
Number of pages6
Pages (from-to)591-596
Early online date28/04/06
Original languageEnglish


Parasitism is a serious challenge to herbivore health and fitness. To avoid parasites, herbivores avoid grazing near feces, creating a mosaic of contaminated tall avoided areas (tussocks) and noncontaminated short grazed areas (gaps). The mosaic represents a nutrition versus parasitism trade-off in that feces-contaminated tussocks are localized concentrations of both forage resources and parasites. Here, we use a grazing experiment with a natural tussock-gap mosaic to determine how the nutritional environment and reproductive effort affect sheep grazing decisions when faced with this trade-off. There were 3 animal treatments (Barren ewes, ewes suckling a single lamb, and ewes suckling twin lambs) and 2 environment treatments (low and high nitrogen). Sward selection and grazing behavior were measured using focal observations on grazing ewes. Sheep showed an overall strong and significant avoidance of tussocks across all treatments. However, there was a reduction in the avoidance of tussocks by ewes on the low-nitrogen (low-N) plots. Ewes suckling twins showed a reduced avoidance of tussocks compared with barren ewes. Lactating ewes in low-N environments further reduced their avoidance of tussocks. Ewes with twins, which are at greatest risk from parasites, had the greatest contact with feces and thus parasites, especially in low-N environments. We conclude that twin-bearing ewes accept the increased risk of parasitism in order to gain the nutrients required to support increased reproductive effort, thus increasing their investment in current offspring at the cost of increased risk of parasitism and thus future potential reproductive attempts. © The Author 2006. Published by Oxford University Press on behalf of the International Society for Behavioral Ecology. All rights reserved.

    Research areas

  • Feces avoidance, Fitness, Grazing, Maternal investment, Parasite risk

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