SUCCESSIONAL TRENDS IN INSECT HERBIVORE POPULATION-DENSITIES - A FIELD-TEST OF A HYPOTHESIS

(1) Theory suggests that plants typical of early and late succession should possess qualitatively different anti-herbivore chemical defences. Differences in the structure, mode of action and effect of these chemicals should result in greater herbivore population levels on plants of early succession. (2) This theory was tested for three separate insect taxa over a successional gradient in southern England. (3) All taxa displayed greater population densities on short-lived plants of early succession than on birch, a plant of late succession. (4) Although the results support theories which suggest a dichotomy of effect of the chemical defences of early and late successional plants, difficulties remain in reconciling the theory of plant chemical defences with existing data.