Trophic cascade

For example, it can be important for understanding the knock-on effects of removing top predators from food webs, as humans have done in many places through hunting and fishing.

Studies have shown that certain invasive species have begun to shift cascades; and as a consequence, ecosystem degradation has been repaired.

[5] This subsidy allowed native animal populations to increase, which then triggered powerful secondary ‘cascading’ effects on forest tree community.

Such cross-boundary subsidy cascades may be widespread in both terrestrial and marine ecosystems and present significant conservation challenges.

For example, a study was conducted to determine the cost of potential stored carbon in living kelp biomass in sea otter (Enhydra lutris) enhanced ecosystems.

[8] Aldo Leopold is generally credited with first describing the mechanism of a trophic cascade, based on his observations of overgrazing of mountain slopes by deer after human extermination of wolves.

[9] Nelson Hairston, Frederick E. Smith and Lawrence B. Slobodkin are generally credited with introducing the concept into scientific discourse, although they did not use the term either.

The green world hypothesis is credited with bringing attention to the role of top-down forces (e.g. predation) and indirect effects in shaping ecological communities.

Although Hairston, Smith and Slobodkin formulated their argument in terms of terrestrial food chains, the earliest empirical demonstrations of trophic cascades came from marine and, especially, aquatic ecosystems.

Additionally, well documented trophic cascades at that point in time all occurred in food chains with algae as the primary producer.

Trophic cascades, Strong argued, may only occur in communities with fast-growing producers which lack defenses against herbivory.

[23] In contrast, a study published in 2009 demonstrated that multiple species of trees with highly varying autecologies are in fact heavily impacted by the loss of an apex predator.

[24] Another study, published in 2011, demonstrated that the loss of large terrestrial predators also significantly degrades the integrity of river and stream systems, impacting their morphology, hydrology, and associated biological communities.

[25] The critics' model is challenged by studies accumulating since the reintroduction of gray wolves (Canis lupus) to Yellowstone National Park.

Healthy Pacific kelp forests, like this one at San Clemente Island of California's Channel Islands , have been shown to flourish when sea otters are present. When otters are absent, sea urchin populations can irrupt and severely degrade the kelp forest ecosystem.
This diagram illustrates trophic cascade caused by removal of the top predator. When the top predator is removed the population of deer is able to grow unchecked and this causes over-consumption of the primary producers.