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Ecological release occurs when a species expands its niche within its own habitat or into a new habitat where there is little competition for resources, which remain abundant.

Origin
The term “ecological release” first appeared in the scientific literature in 1972 in the American Zoologist Journal discussing the effects of the introduction of a sea snail on an isolated ecosystem, Easter Island. One of the first studies that linked niche shifts to the presence and absence of competitors was by Lack and Southern where habitat broadness of song birds was positively correlated to the absence of a related species.

Common Example
Invasive species are an excellent example of successful ecological release because low levels of biodiversity, an abundance of resources, and particular life history traits allow their numbers to increase dramatically. Additionally, there are few predators for these species.

Cascade effect
When a keystone species, such as a top predator, is removed from a community or ecosystem, a cascade effect can occur through which a series of secondary extinctions take place. Keystone predators are responsible for the control of prey densities, and their removal can result in an increase in one or a number of predators, consumers, or competitors elsewhere in the food web. Several prey or competitor species can consequently suffer a population decline and potentially be extirpated; the result of this would be a decrease in community diversity. Without the keystone species, prey populations can grow indefinitely and will, ultimately, be limited by resources such as food and shelter. Due to these secondary extinctions, a niche is left unfilled: this allows a new species to invade and exploit the resources that are no longer being used by other species.