Trophic Cascades.

In many ecosystems, apex consumers (top predators) play a crucial role in food web dynamics. Their top-down impacts are known to spread downwards through the food webs in a cascading fashion. Trophic cascades manifest when top predators are excluded from an ecosystem or introduced into a system lacking them. Two such case studies are described here. Trophic cascades are generally more pronounced in the aquatic than in the terrestrial ecosystems, which in turn is related to the differences in the average body sizes of herbivores relative to the plant resources they feed upon and in the structure of their food webs. Scientists express concern that human activities have been leading to planet-wide trophic downgrading (loss of apex consumers) which could affect vital ecological processes of the biosphere. [ABSTRACT FROM AUTHOR]