Assessing climatic and intrinsic factors that drive arthropod diversity in bird nests

Bird nests are specialized structures that act as microrefuge and a source of food for arthropods. Nest arthropod richness and composition may vary according to the nest builder, geographical location and nest size. Because information on nest arthropods is scarce, there are even fewer studies on the drivers of nest arthropod diversity. We characterized arthropod diversity in cup- and dome-shaped nests along a 130 km latitudinal gradient in the mediterranean-type region of Central Chile and, we assessed whether nest dimensions and climatic factors explain richness (alpha-diversity). Then, we evaluated whether climatic differences between sites explain arthropod nest composition (beta-diversity). All collected nests hosted at least one arthropod specimen. We identified 43 taxonomic entities (4.2 entities per nest ± 0.5, mean ± SE, n = 27 nests) belonging to 18 orders and five classes: Arachnida, Diplopoda, Entognatha, Insecta and Malacostraca. We observed differences in nest arthropod richness and composition related to sites but not bird species. Larger nests supported greater arthropod richness. Furthermore, we observed that climatic differences explain the variation in arthropod composition between sites. Nests in the northern region (drier and warmer) mainly hosted Hemipterans and Hymenopterans. Contrary, nests in the southern region (humid and colder) hosted species of Collembola, Dermaptera, and Diplopoda. Positive relationship between nests surface area with arthropod richness suggests us that larger nests may keep more resources. Our study sheds light on a crucial interaction which may have potential consequences for insect assemblage composition and bird reproductive biology.