Seasonal patterns in species richness of herbivores: Macrolepidopteran larvae on Finnish deciduous trees

Abstract. 1. The seasonal distribution of macrolepidopteran species richness on Finnish deciduous trees vaned from positively skewed (peak in spring) to negatively skewed (peak in autumn). 2. The skewness values of species richness had a significant negative correlation ( r = ‐ 0.98) with the duration of the seasonal shoot‐growth period of the tree species. 3. Trees which complete their shoot growth early in the season ( Quercus type) produce new leaves only during spring, while trees whose shoot growth continues to autumn ( Populus type) do so throughout the summer. 4. Consequently, there is a difference in the number of available resources in the late summer foliage of different tree species, Trees ceasing leaf production early such as oak ( Quercus robur ) and bird cherry ( Prunus padus ) have one major resource type (mature leaves) in late‐season foliage while trees like birches and alders have two Ooung and mature leaves). 5. Because young leaves formed late in the season are preferred to mature ones by some species of herbivores and because other species prefer mature leaves at the same time, the species richness of Populus‐type trees is higher later in the season than the species richness of Quercus‐type of trees, which have just one type of resource available.