Habitat use of coexisting Microtus vole species under competition and predation risk
​The experimental enclosure showing the boundary between short and tall grasses (photo Elina Koivisto)

​A trade-off between safety and food quality affected by nasty neighbours

The short grass habitat was kept sort by regular mowing, producing constantly new shoots but providing less cover against avian predators, thus creating a more productive but less safe habitat. The tall grass parts were left untouched as a safer but poorer habitat type. Our previous studies have shown that in the absence of predation sibling voles are competitively superior to field voles on a population level but more vulnerable to predation, which probably explains why field voles are more numerous in nature. Sibling voles have been found to inhabit more cultivated fields than field voles, so they have been thought to favour these habitats.
Somewhat contrary to our expectations, when the species occurred alone and without predation risk, sibling voles used less of the short grass habitat than what field voles did. When the interspecific competitor was added to the picture, field voles decreased and sibling voles increased their use of short grass habitat. When the habitat use patterns were studied under interspecific competition and natural predation risk, the species behaved as previously described: sibling voles used the low cover habitat proportionally more than field voles.
The use of low cover habitat observed in sibling voles in the absence of predators in single-species populations without competition and in mixed-species populations with competition suggests that sibling voles use more the safe habitat when there are no competitors, but are prone to use the more risky habitat when competitors are present, indicating that the fitness benefits of each habitat depend on the presence or absence of competitors. Our results thus highlight the importance of including effects of both predation risk and competition when interpreting the patterns of habitat distribution observed in nature among coexisting species and not take them solely as a result of one or the other

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-Elina Koivisto