Effects of Isolation on the Occurrence of a Fungivorous Forest Beetle, Bolitotherus cornutus, at Different Spatial Scales in Fragmented and Continuous Forests

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Abstract
We investigated the effect of spatial isolation on the incidence of a fungivorous forest beetle in continuous and fragmented forests at three spatial scales, while controlling for confounding variables, such as patch size and duality. Isolation was measured using nearest-neighbour distances and we compared the usefulness of measuring multiple patches and considering either occupied or unoccupied patches. An effect of spatial isolation on beetle incidence was evident at all three scales: between fungal carps on a log (0 to 2 m), between carp clusters in a forest (1 to 71 m) and between woodlots in an agricultural matrix (25 to 2000 m). The magnitude of the isolation effect was stronger at the largest scale than at the smallest scale. However. isolation was most prevalent (i.e. significant for all measures of isolation) at the intermediate scale. The effect of isolation was not influenced by forest configuration type (continuous or fragmented) or by patch density, but there was a marginal compensatory effect of patch size on isolation. Isolation measures incorporating only occupied patches were not generally better predictors than isolation measures incorporating all patches. Little information would have been lost by using only the distance to the closest patch to measure isolation effects, rather than incorporating distances to multiple patches.