Community Assembly and Spatial Ecology of Saproxylic Coleoptera

Abstract: Community assembly is the process deciding inclusion/exclusion of species in a developing community. Spatial ecology integrates spatial habitat factors with local biotic interactions within a given patch.I used standardized tree bolts (0.35-1 m long) to sample saproxylic (wood living) beetles in natural and managed forest types.Density-dependent effects were more intense in old-growth coniferous forest than in burnt forest. The final-state assemblages in these two forest types diverged regarding species composition but converged regarding community structure. The communities also followed forest-type specific assembly trajectories.Order of arrival can influence the species assemblage, I found priority effects when comparing the reproductive success of two cerambycid species. A two-week head start had a positive effect on fitness in both species. Different fitness components were affected in the two species: offspring number in Acanthocinus aedilis and offspring quality in Rhagium inquisitor.In birch-living Coleoptera a large part of variance in species composition could be explained by habitat variables (22.9 %), such as forest type, or spatial variables (15.8 %), such as distance apart. The assemblages in deciduous sites responded to distance apart and showed positive spatial autocorrelation up to a distance of 80 km. For assemblages in deciduous sites a metacommunity perspective is warranted – on a surprisingly large scale.I compared two regions, one more fragmented and one less fragmented, (with 2.2 % more deciduous forest in the landscape). The effects of habitat fragmentation was primarily found in mature coniferous forest. Host-tree patches in this matrix forest were perceived as matrix by the Coleoptera in the more fragmented region but as habitat in the less fragmented region.Some of my study sites consisted of protected old-growth forest. These were embedded in a landscape dominated by forestry. These protected areas were invaded by generalist species, thriving in managed forests.