SPECIALIZATION OF PHYTOPHAGOUS ARTHROPOD COMMUNITIES ON INTRODUCED PLANTS

Arthropod herbivore communities vary in the proportion of plant family specialists and broad generalists. Examination of the literature of 23 annual crop plant species and the associated feeding relations of 498 arthropod species in Japan revealed that contemporary cropping area was only weakly associated with current arthropod species richness, and that the proportion of plant family specialists was greater and the proportion of generalists was lower on plant species that had been in Japan for longer periods of time. These results suggest that arthropod communities become increasingly more specialized or less generalized the longer a plant coexists with the community, and that this process can occur over time periods of a few thousand years. Exotic arthropod species associated with these plants and known to have invaded Japan in the last 100-200 yr are more generalized than the native fauna, so species invasions could not contribute to the increased specialization or decreased generalization with time.