Density-dependent foraging behaviour of sheep on alpine pastures: effects of scale

• Published in: Journal of zoology (1987) 2006-09, Vol.270 (1), p.63-71
• Main Authors: Kausrud, K., Mysterud, A., Rekdal, Y., Holand, Ø., Austrheim, G.
• Format: Article
• Language: English
• Subjects: Animal behavior; Animal populations; Deschampsia flexuosa; non-linear effects; Population density; population processes; Sheep; ungulates; vegetation types; Zoology
• ISSN: 0952-8369; 1469-7998
• DOI: 10.1111/j.1469-7998.2006.00118.x

Foraging patterns of large herbivores may give important clues as to why their life history varies depending on population density. In this landscape‐scale experiment, domestic sheep Ovis aries were kept at high (80 sheep km−2) and low (25 sheep km−2) population densities during summer in high mountain pastures in Hol, Norway. We predicted an increasing use of less preferred plant species or habitat types with increasing sheep population density. Foraging behaviour was investigated by direct observations of individually marked sheep on different spatial scales, and diet composition was also assessed with microhistological analysis of faecal samples from known individuals. We found that the effects of density on foraging behaviour depended on scale and were only detected at the scale of diet choice. Use of the common grass species Deschampsia flexuosa, which provided the bulk forage (10–65% of the diet), remained constant throughout the season at low densities, but increased significantly over time at high densities. On a coarser spatial scale, neither within vegetation type nor between vegetation types, selection was affected by density, but vegetation type selection differed depending on whether the sheep were grazing or resting. Our study provides evidence of density dependence in foraging behaviour, but only at the finest spatial scale (diet choice).