Vegetation complexity-The influence of plant species diversity and plant structures on plant chemical complexity and arthropods

Vegetation complexity is characterized by two major traits, i.e., plant chemical and plant structural complexity. Plant species diversity strongly determines these traits. Furthermore, plant structures affect microclimatic conditions, which in turn influence the emission and dispersion of plant volatiles (e.g., chemical complexity). Plant volatile chemical complexity may significantly affect orientation of herbivorous and carnivorous arthropods. Therefore, the way in which plant chemical and plant structural complexity act in concert may influence foraging and mating success of arthropods, and thus, finally, community composition. This review emphasizes an integrative view on the relationship between plant species diversity, plant structural complexity, plant volatiles (chemical complexity) and their effects on arthropods. Three new hypotheses are raised, which predict possible relations between plant volatile complexity and plant species diversity: ( 1) saturation-, (2) step-by-step, (3) incoherence-hypothesis. We conclude that arthropod orientation in natural environments is strongly determined by the relationship between plant volatile diversity and plant species diversity. Furthermore, we emphasize that structural complexity of the vegetation affects plant volatile diversity and thus, arthropod orientation. We review available information on how insects actually respond to complexity during olfactory and visual search and ask for both laboratory and field studies to further unravel the mechanisms of interactions between vegetation traits and their impact on arthropod orientation.