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Multiple predators induce risk reduction in coexisting vole species


  • Katrine S. Hoset,

  • Elina Koivisto,

  • Otso Huitu,

  • Hannu Ylönen,

  • Erkki Korpimäki

K. S. Hoset (, E. Koivisto, O. Huitu and E. Korpimäki, Dept of Biology, Univ. of Turku, FI–20014 Turku, Finland. OH also at: Finnish Forest Research Institute, Suonenjoki Unit, Juntintie 154, FI–77600 Suonenjoki, Finland. – H. Ylönen, Dept of Biological and Environmental Science and Konnevesi Research Station, Univ. of Jyväskylä, PO Box 35, FI–40014 Univ. of Jyväskylä, Finland.


Large predators may affect the hunting efficiency of smaller ones directly by decreasing their numbers, or indirectly by altering their behaviour. Either way this may have positive effects on the density of shared prey. Using large outdoor enclosures, we experimentally studied whether the presence of the Tengmalm's owl Aegolius funereus affects the hunting efficiency of the smallest member of the vole-eating predator guild, the least weasel Mustela nivalis, as measured by population responses of coexisting prey species, the field vole Microtus agrestis and the sibling vole M. levis. We compared the density and survival probability of vole populations exposed to no predation, weasel predation or combined predation by a weasel and an owl. The combined predation of both owl and weasel did not result in obvious changes in the density of sibling and field vole populations compared to the control populations without predators, while predation by least weasel alone decreased the densities of sibling voles and induced a similar trend in field vole densities. Survival of field voles was not affected by predator treatment while sibling vole survival was lower in predator treated populations than in control populations. Our results suggest that weasels are intimidated by avian predators, but without changing the effects of predators on competitive situations between the two vole species. Non-lethal effects of intraguild predation therefore will not necessarily change competitive interactions between shared prey species.