The effect off sheep grazing on beetles and spiders in alpine ecosystem

Aaserud, Ragnar Mathias; Atle Mysterud

The effect off sheep grazing on beetles and spiders in alpine ecosystem

2006

Aaserud, Ragnar Mathias | Atle Mysterud

Invertebrate community responses to grazing were studied within a fully replicated,landscape scale experiment where densities of domestic sheep were manipulated in alpine ecosystems in Hol, Norway. I determined species richness and abundance of beetles and spiders with pitfall trapping in each of the enclosures with three different levels of sheep densities (no, low and high). Strong effects of sheep grazing on the species richness and abundance of beetles were found. Species richness was lower at high density of sheep compared to treatments with low density or no sheep. There was however no difference in species richness between enclosures with low density or no sheep present. The abundance of both of the two most common herbivore beetles was negatively affected by grazing. Byrrhus fasciatus (Byrrhidae) was negatively affected even at low densities of sheep. Only Patrobus assimilis (Carabidae) of the three predatory beetles were reduced in abundance due to grazing and then only at high sheep density. The abundance of the other two predator beetles species as well as the spider community, which are also predators, were not affected by sheep grazing to the same extent. The insight obtained from this study is thus that sheep grazing is affecting the invertebrate community, but that effects differ between different functional groups, being stronger for herbivores than predators. Although this is based on analyses of a limited number of species, it may suggest that the effect of sheep grazing diminishes further up the food chain.

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