Abstract
The evolutionary split between gymnosperms and angiosperms has far‐reaching implications for the current communities colonizing trees. The inherent characteristics of dead wood include its role as a spatially scattered habitat of plant tissue, transient in time. Thus, local assemblages in deadwood forming a food web in a necrobiome should be affected not only by dispersal ability but also by host tree identity, the decay stage and local abiotic conditions. However, experiments simultaneously manipulating these potential community drivers in deadwood are lacking. To disentangle the importance of spatial distance and microclimate, as well as host identity and decay stage as drivers of local assemblages, we conducted two consecutive experiments, a 2‐tree species and 6‐tree species experiment with 80 and 72 tree logs, respectively, located in canopy openings and under closed canopies of a montane and a lowland forest. We sampled saproxylic beetles, spiders, fungi and bacterial assemblages from logs. Variation partitioning for community metrics based on a unified framework of Hill numbers showed consistent results for both studies: host identity was most important for sporocarp‐detected fungal assemblages, decay stage and host tree for DNA‐detected fungal assemblages, microclimate and decay stage for beetles and spiders and decay stage for bacteria. Spatial distance was of minor importance for most taxa but showed the strongest effects for arthropods. The contrasting patterns among the taxa highlight the need for multi‐taxon analyses in identifying the importance of abiotic and biotic drivers of community composition. Moreover, the consistent finding of microclimate as the primary driver for saproxylic beetles compared to host identity shows, for the first time that existing evolutionary host adaptions can be outcompeted by local climate conditions in deadwood.
Highlights
Understanding how organisms interact with their local environment and what determines changes in species composition in space and time is a central goal of ecology (Dornelas et al 2014)
Variation partitioning for community metrics based on a unified framework of Hill numbers showed consistent results for both studies: host identity was most important for sporocarp-detected fungal assemblages, decay stage and host tree for DNAdetected fungal assemblages, microclimate and decay stage for beetles and spiders and decay stage for bacteria
We found that for taxa closely associated with dead wood, i.e. beetles, bacteria and fungi, more of the variance was explained by biotic factors, such as decay stage and host species, than by microclimate
Summary
Understanding how organisms interact with their local environment and what determines changes in species composition in space and time is a central goal of ecology (Dornelas et al 2014). The relative contribution of rare, common and dominant (i.e. based on abundances) species in local communities is thought to be important in determining such dissimilarities (Norden et al 2009, 2017, Thorn et al 2020). While stochastic factors will always hinder exact predictions, important deterministic controls on community composition do exist and, following the work of Diamond (1975), much attention has been given to elucidating the rules of community assembly (Weiher and Keddy 1999, Temperton et al 2004, Friedman et al 2017, Pearson et al 2018). The relative importance and permeability of these filters may be highly dynamic, depending on the environmental context and the specific taxon
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