Ecological release

Ecological release occurs when a species is introduced to an environment other than its native habitat The foreign species either flourishes into a local population or dies out. Not all released species will become invasive; most released species that don’t immediately die out tend to find a small niche in the local ecosystem. Ecological release also occurs when a species expands its niche within its own habitat or into a new habitat.^[1]

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.^[2] One of the first studies that linked niche shifts to the presence and absence of competitors was by Lack and Southern^[3] 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.

Causes and mechanisms

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.^[4] 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.^[4] 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.^[4]

Human causes ecological release

Ecological Release by human means, intentional on unintentional, has had drastic effects on ecosystems worldwide. The most extreme examples of Invasive Species include: Cane Toads in Australia,^[5] Kudzu in the Southeast United States,^[6] or Beavers in Tierra Del Fuego. But ‘’ecological release’’ can also be more subtle, less drastic and easily overlooked such as Mustangs and Dandelions in North America,^[7] Musk Oxen in Svalbard,^[8] Dromedaries in Australia, or Peaches in Georgia^[9]

References