Primary Productivity and Trophic Dynamics Investigated in a North Derbyshire, UK, Dale

Trophic interactions were investigated on herbaceous communities in a limestone dale in Northern England. Manipulative experiments involved the application of molluscicides and foliar and soil insecticides along natural productivity gradients. The results supported the theories of Fretwell and Oksanen in which trophic dynamics are predicted to be dependent upon primary productivity. Furthermore, the results extend the Fretwell-Oksanen model by the inclusion of invertebrates, and the applicability of the model to the small, individual habitat scale. At very low productivity, the vegetation was dominated by slow-growing, unpalatable species and did not experience a detectable amount of herbivory. In circumstances of high productivity, 'top-down' control of herbivores by carnivores appeared to protect the resident fast-growing and relatively palatable perennials from herbivory. Vegetation of intermediate productivity responded strongly to the removal of herbivores; here we conclude that herbivore pressure is high because productivity is insufficient to sustain a high intensity of 'top-down' control from carnivores.