Spatio-temporal species aggregations do not rule out interspecific competition in tree hollow spider assemblages

Abstract

A community's biological diversity reflects coexistence between species. This often depends, to some extent, on whether there is competition for resources and how it is dealt with. The nature of old-growth tree hollows is confined and relatively isolated, which makes them ideal for investigating the competition phenomena between their inhabitants, such as Araneae. The existence of interspecific competition in the structuring of tree hollow spider assemblages in Mediterranean forests was inferred by spatial co-occurrence pattern analyses with null models at both the community and pairwise levels. The analysis included 36 spider species collected monthly with emergence traps for 1 year. The distribution of four ecological traits, body size and phenology on the resulting pattern type was discussed. The analyses showed spatial segregation at the community level and spatial aggregations between species with different traits predominated at the pairwise level. Hunting strategy and body size were the main differential traits to facilitate these aggregations. In addition, only the aggregations led by Amaurobius scopolii–Scotophaeus scutulatus and Eratigena atrica–Liocranum majus also showed an overlap during their main activity period. Community segregation and spatio-temporal aggregations of species with differential traits suggest that interspecific competition is a very likely structuring factor of tree hollow spider assemblages. Instead, segregations at the pairwise level seem to result from other factors, for example, habitat preferences.