Bromeliad architectural complexity and vertical distribution predict spider abundance and richness

Habitat complexity is a main predictor of the distribution of arthropods on vegetation. However, it remains poorly known whether plant architecture and fine-scale spatial distribution affect the species richness and composition of associated arthropod guilds. In this study, we extensively sampled bromeliad species with a variety of rosette architectures in a megadiversity region. The aims were to investigate whether (i) possible differences in spider species composition among bromeliad species are related to the distinct architectures of the plants, and (ii) bromeliad architectural complexity (an intrinsic feature) and vertical distribution (an extrinsic feature) are good predictors of spider abundance and richness. Contrary to our expectations, spider species composition did not vary significantly among bromeliad species with different architectures. We found a positive effect of the mean number of leaves on spider abundance and species richness, but it occurred indirectly through spider abundance; factoring out the indirect effect revealed a negative effect of leaf number on species richness. Bromeliad species with wider vertical distributions harboured more spider species. Our results suggest that the dominance of a few spider species and reduced space for orb-web spiders to attach their webs are the main explanations for lower spider richness on bromeliad species with higher architectural complexity. Our findings highlight the importance of both intrinsic and extrinsic plant features as co-determinants of predator arthropod diversity.