ARE TROPHIC CASCADES ALL WET - DIFFERENTIATION AND DONOR-CONTROL IN SPECIOSE ECOSYSTEMS

Trophic cascades mean runaway consumption, downward dominance through the food chain, with autotrophs being particularly vulnerable. Standing crop and coverage of the plant community are reduced wholesale when one or a few species of potent herbivores are not suppressed. Primary carnivores or diseases, by suppressing herbivores, switch the substrate from open to well-occupied by plants. In true trophic cascades, pervasive top-down influence combines with the always strong bottom-up influence through the food chain to produce acute intertwining between population, community and ecosystem processes. True trophic cascades imply keystone species, taxa with such top-down dominance that their removal causes precipitous changes in the system. The author's premise is that true cascades in the community sense are a relatively unusual sort of food web mechanics. Over the full range of ecological communites, evidence is that these cascades are restricted to fairly low-diversity places where great influence can issue from one or a few species. Most examples of true trophic cascades have algae at the base and are aquatic. The author demonstrates the vulnerability of the turf of some algal ecosystems, emphasises that not all algal ecosystems cascade, examines reticulate webs in high-diversity systems, and considers the architecture depicted in true trophic cascades (reminiscent of a ladder) with trophic webs. -from Author