How does plant diversity influence the function of a young coastal ecosystem as arthropod habitat?

Background/Question/Methods   While there is general agreement that species diversity influences ecosystem function, the mechanisms behind observed patterns and the relative importance of these relationships has been debated. Diversity-function relationships may change with ecosystem successional stage and focal function. Here, we determine the effects of plant diversity on the arthropod habitat function of a young coastal transition ecosystem by testing several diversity-function theories, including sampling effect, facilitation and complementarity effect. We sampled the canopy arthropods from each individual plant within each treatment plot, where treatment is plant species diversity level. Along with plant abundance, complexity and quality data, we explored whether arthropods were responding to one particular species in the mix (e.g., sampling effect), to physical attributes of one or more species (e.g., facilitation), and/or to a mix of trophic and physical attributes contributed by the various species (e.g., complementarity effect).

Results/Conclusions   We found that relationships varied with elevation, and taxonomic and functional groups. Total arthropod abundances and proportions of introduced species (mostly the Argentine ant) increased with the presence and abundance of particular species and milder physical condition (i.e, sampling effect and facilitation), while arthropod diversity increased with total plant complexity of the plot (i.e., facilitation). Proportions of several herbivores responded to a mix of plant complexity and the abundance and quality of particular species (i.e., complementarity), and proportions of predators increased mostly with increased plant complexity (i.e., facilitation). We see that multiple mechanisms are acting across space and trophic hierarchies. Our findings in this young system are informing current efforts to restore native plant and arthropod communities.