Functional traits and community assembly of ground invertebrates in an experimental grassland

Background/Question/Methods

To assess functional diversity and functional community assembly, a first step is the identification of core functional traits for a group of organisms.  We used a process similar to what has been used for plants in order to, first, identify the principal challenges faced by ground-dwelling macroinvertebrates, and then, identify functional trait sets for characterizing abilities associated with meeting those challenges.  In addition, we created pragmatic analogs for the more difficult traits.  We identified challenges that included: (1) resource acquisition, (2) predator avoidance including movement/motility, defenses, camouflage/warning coloration, time of activity, (3) competition, (4) stress avoidance in terms of seasonality, dormancy, and diapause.  We chose a set of functional traits related to (1) body size, (2) motility, (3) perception of surroundings, (4) physical defenses against predators, (5) feeding/mouthparts, (6) color (camouflage/warning) that address many of the identified challenges.  We calculated their functional diversity as trait range, minimum spanning tree, neighbor distance, nearest-neighbor distance, sd of the former, and Simpson’s FD.  We calculated the standardized effect size (SES) to assess deviations from neutral assembly.  We also investigated the influence of historical treatments of nitrogen and fungcide on functional diversity.

 Results/Conclusions

We quantified 15 functional traits (other than color) in 45 taxa (mainly families) of terrestrial ground-dwelling macroinvertebrates to understand their functional diversity and community assembly.  Principal component analysis suggested the trait space was complex, in that five principal components were necessary to account for 75% of the variation in trait values.  The first two pcs separated arachnids from the other taxa, while subsequent pcs mainly extracted taxa with extreme morphologies (e.g., Opiliones, Myriapods). Patterns of functional diversity (trait dispersion) were consistent with neutral assembly processes.  SES values were consistently between -2 and +2 for both individual principal components and the five taken together.  In addition, we found no significant influence of historical chemical treatments (nitrogen, fungicide) on functional diversity, which further supports predominantly neutral assembly processes.  Our next step is to consider influences of vegetation, including its functional diversity.