Abstract
Arboreal spiders in deciduous and coniferous trees were investigated on their distribution and diversity. Insecticidal knock-down was used to comprehensively sample spiders from 175 trees from 2001 to 2003 in the Białowieża forest and three remote forests in Poland. We identified 140 species from 9273 adult spiders. Spider communities were distinguished between deciduous and coniferous trees. The richest fauna was collected from Quercus where beta diversity was also highest. A tree-species-specific pattern was clearly observed for Alnus, Carpinus, Picea and Pinus trees and also for those tree species that were fogged in only four or three replicates, namely Betula and Populus. This hitherto unrecognised association was mainly due to the community composition of common species identified in a Dufrene-Legendre indicator species analysis. It was not caused by spatial or temporal autocorrelation. Explaining tree-species specificity for generalist predators like spiders is difficult and has to involve physical and ecological tree parameters like linkage with the abundance of prey species. However, neither did we find a consistent correlation of prey group abundances with spiders nor could differences in spider guild composition explain the observed pattern. Our results hint towards the importance of deterministic mechanisms structuring communities of generalist canopy spiders although the casual relationship is not yet understood.
Highlights
Spiders are a prominent group of predators in ecosystems and have received increasing interest in research during the last years [1,2,3,4]
In temperate forests, canopy spiders contribute between 4% and 12% to the arboreal arthropod fauna playing an important role in the regulation of insect populations [5,6]
Spiders are mostly generalist predators and canopy spiders are assumed to be little associated with their host trees, habitat structure and microclimatic conditions influence the distribution of many spiders [7,8,9]
Summary
Spiders are a prominent group of predators in ecosystems and have received increasing interest in research during the last years [1,2,3,4]. Considering the canopy in ecological research is expected to foster our understanding of the relationships and species interactions that govern ecosystem processes and ecosystem function. Understanding the assembly rules of spider communities can provide valuable information towards these processes and is an important issue in basic ecological research. Apart from that, spiders are not known to discriminate between tree species. Prey availability is another factor potentially influencing the distribution of spiders and community composition but the evidence is contradictory indicating positive as well as negative relationships [7,11,12,13]
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