Spatio-temporal variation in Lepidopteran larval assemblages associated with oak, Quercus crispula:: the importance of leaf quality

1. Lepidoptera larval abundance and diversity in the canopies of oak (Quercus crispula) trees and saplings were surveyed in a cool-temperate, deciduous broadleaf forest in northern Japan. 2. In general, newly developed leaves were soft, rich in water and nitrogen, and low in tannin, whereas they became tough, poor in water and nitrogen, and high in tannin as the season proceeded. Leaf quality also varied among forest strata, such variations resulting in seasonal and among-strata differences in the structure of the Lepidoptera larval assemblage. 3. The greater Lepidoptera larval abundance and species richness may related to the higher leaf quality on spring foliage compared with summer foliage. On the other hand, diversity (Shannon's H') and evenness (Pielou's J') were greater on summer foliage than on spring foliage. Strengthened defences of the host plants against herbivory may cause these differences by filtering the larvae of Lepidoptera species and by constraining the super-dominance of a few species on summer foliage. 4. Canonical Correspondence Analysis (CCA) ordination also revealed a stratified structure of the Lepidoptera larval assemblage in the forest. In both spring and summer, the assemblage composition was more similar between sunlit and shaded canopies than between canopies and saplings. Such assemblage stratification was highly correlated with toughness and tannin content (in spring and summer) or water content (in summer). 5. This study emphasised the importance of spatio-temporal variations in leaf quality, even within the same host plant species, for promoting herbivore diversity in forests.