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The mesopredator release hypothesis is an
ecological Ecology () is the study of the relationships between living organisms, including humans, and their physical environment. Ecology considers organisms at the individual, population, community, ecosystem, and biosphere level. Ecology overlaps w ...
theory used to describe the interrelated
population dynamics Population dynamics is the type of mathematics used to model and study the size and age composition of populations as dynamical systems. History Population dynamics has traditionally been the dominant branch of mathematical biology, which has a ...
between
apex predator An apex predator, also known as a top predator, is a predator at the top of a food chain, without natural predators of its own. Apex predators are usually defined in terms of trophic dynamics, meaning that they occupy the highest trophic lev ...
s and
mesopredator A Mesopredator is a mid-ranking predator in a trophic level, which typically prey on smaller animals. Mesopredators often vary in ecosystems depending on the food web. While there is no definitive measurement for mesopredators, they are usually ref ...
s within an
ecosystem An ecosystem (or ecological system) consists of all the organisms and the physical environment with which they interact. These biotic and abiotic components are linked together through nutrient cycles and energy flows. Energy enters the syst ...
, such that a collapsing population of the former results in dramatically increased populations of the latter. This hypothesis describes the phenomenon of
trophic cascade Trophic cascades are powerful indirect interactions that can control entire ecosystems, occurring when a trophic level in a food web is suppressed. For example, a top-down cascade will occur if predators are effective enough in predation to reduce t ...
in specific terrestrial
communities A community is a social unit (a group of living things) with commonality such as place, norms, religion, values, customs, or identity. Communities may share a sense of place situated in a given geographical area (e.g. a country, village, tow ...
. A mesopredator is a medium-sized, middle
trophic level The trophic level of an organism is the position it occupies in a food web. A food chain is a succession of organisms that eat other organisms and may, in turn, be eaten themselves. The trophic level of an organism is the number of steps it i ...
predator, which both preys and is preyed upon. Examples are
raccoon The raccoon ( or , ''Procyon lotor''), sometimes called the common raccoon to distinguish it from other species, is a mammal native to North America. It is the largest of the procyonid family, having a body length of , and a body weight of ...
s,
skunk Skunks are mammals in the family Mephitidae. They are known for their ability to spray a liquid with a strong, unpleasant scent from their anal glands. Different species of skunk vary in appearance from black-and-white to brown, cream or ginge ...
s,
snake Snakes are elongated, limbless, carnivorous reptiles of the suborder Serpentes . Like all other squamates, snakes are ectothermic, amniote vertebrates covered in overlapping scales. Many species of snakes have skulls with several more joints ...
s,
cownose ray The cownose ray (''Rhinoptera bonasus'') is a species of Batoidea found throughout a large part of the western Atlantic and Caribbean, from New England, United States to southern Brazil (the East Atlantic populations are now generally considered ...
s, and small sharks.


The hypothesis

The term "mesopredator release" was first used by Soulé and colleagues in 1988 to describe a process whereby mid-sized
carnivorous A carnivore , or meat-eater (Latin, ''caro'', genitive ''carnis'', meaning meat or "flesh" and ''vorare'' meaning "to devour"), is an animal or plant whose food and energy requirements derive from animal tissues (mainly muscle, fat and other so ...
mammals became far more abundant after being "released" from the control of a larger carnivore. This, in turn, resulted in decreased populations of still smaller
prey Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not kill the ...
species, such as birds. This may lead to dramatic prey population decline, or even
extinction Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and ...
, especially on islands. This process arises when mammalian top predators are considered to be the most influential factor on
trophic Trophic, from Ancient Greek τροφικός (''trophikos'') "pertaining to food or nourishment", may refer to: * Trophic cascade * Trophic coherence * Trophic egg * Trophic function * Trophic hormone * Trophic level index * Trophic level * Troph ...
structure and
biodiversity Biodiversity or biological diversity is the variety and variability of life on Earth. Biodiversity is a measure of variation at the genetic (''genetic variability''), species (''species diversity''), and ecosystem (''ecosystem diversity'') le ...
in terrestrial ecosystems. Top predators may feed on herbivores and kill predators in lower
trophic level The trophic level of an organism is the position it occupies in a food web. A food chain is a succession of organisms that eat other organisms and may, in turn, be eaten themselves. The trophic level of an organism is the number of steps it i ...
s as well. Thus, reduction in the abundance of top predators may cause the medium-sized predator population to increase, therefore having a negative effect on the underlying prey community. The mesopredator release hypothesis offers an explanation for the abnormally high numbers of mesopredators and the decline in prey abundance and diversity.Terborgh, J., Estes, J.A., Paquet, P., Ralls, K., Boyd-Heger, D., Miller, B.J. 1999. The role of top carnivores in regulating terrestrial ecosystems. In: Continental conservation: design and management principles for long-term, regional conservation networks. (eds Soulé, M. & Terborgh, J.). Island Press, Covelo, CA; Washington DC. pp. 39–64 The hypothesis supports the argument for conservation of top predators because they protect smaller prey species that are in danger of extinction. This argument has been a subject of interest within conservation biology for years, but few studies have adequately documented the phenomenon.


Criticism

One of the main criticisms of the mesopredator release hypothesis is that it argues in favor of the top-down control concept and excludes the possible impacts that bottom-up control could have on higher
trophic level The trophic level of an organism is the position it occupies in a food web. A food chain is a succession of organisms that eat other organisms and may, in turn, be eaten themselves. The trophic level of an organism is the number of steps it i ...
s. This means that it supports the argument that top predators control the structure and
population dynamics Population dynamics is the type of mathematics used to model and study the size and age composition of populations as dynamical systems. History Population dynamics has traditionally been the dominant branch of mathematical biology, which has a ...
of an ecosystem, but it does not take into account that prey species and primary producers also have an effect on the ecosystem's structure. Furthermore, populations of smaller predators do not ''always'' increase after the removal of top predators; in fact, they sometimes decline sharply. Another problem is that the hypothesis is offered as an explanation after large predators have already become rare or
extinct Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and ...
in an ecosystem. Consequently, there is no data on the past ecosystem structure and the hypothesis cannot be tested. As a result, information on the past conditions has been inferred from studies of the present conditions. However, contemporary examples of mesopredator release exist, such as the culling of cats on
Macquarie Island Macquarie Island is an island in the southwestern Pacific Ocean, about halfway between New Zealand and Antarctica. Regionally part of Oceania and politically a part of Tasmania, Australia, since 1900, it became a Tasmanian State Reserve in 19 ...
. The hypothesis is sometimes also applied to humans as apex predators that produce top-down effects on lower trophic levels. However, it fails to recognize bottom-up effects that anthropogenic land transformations can have on landscapes on which primary producers, prey species, and mesopredators dwell. Possible bottom-up effects on an ecosystem can be from
bioclimatic Green building (also known as green construction or sustainable building) refers to both a structure and the application of processes that are environmentally responsible and resource-efficient throughout a building's life-cycle: from planni ...
impacts on ecosystem productivity and from anthropogenic habitat alterations. Examples of anthropogenic habitat change include agriculture, grazing land, and urbanization. More importantly, the hypothesis does not take into account that higher trophic levels are affected by
primary productivity In ecology, primary production is the synthesis of organic compounds from atmospheric or aqueous carbon dioxide. It principally occurs through the process of photosynthesis, which uses light as its source of energy, but it also occurs through c ...
. It also does not mention that trophic interactions operate at different strengths according to the ecosystem. Therefore, the roles of predation and food/nutrient processes in influencing ecosystem structures remain open to controversy and further testing.


Other release hypotheses

The mesopredator release hypothesis has also inspired other "release hypotheses". For example, the "mesoscavenger release hypothesis", which proposes that when large, efficient, scavenger populations decline (such as vultures), small, less efficient, mesoscavenger populations increase (such as rats). However, this type of release is different. In the mesoscavenger release hypothesis, mesoscavengers are being released from competition for food, whereas, in the mesopredator release hypothesis, mesopredators are being released from direct predation from the apex predators.


See also

*
Biodiversity Biodiversity or biological diversity is the variety and variability of life on Earth. Biodiversity is a measure of variation at the genetic (''genetic variability''), species (''species diversity''), and ecosystem (''ecosystem diversity'') le ...
* Enemy release hypothesis *
Trophic cascade Trophic cascades are powerful indirect interactions that can control entire ecosystems, occurring when a trophic level in a food web is suppressed. For example, a top-down cascade will occur if predators are effective enough in predation to reduce t ...
*
Trophic level The trophic level of an organism is the position it occupies in a food web. A food chain is a succession of organisms that eat other organisms and may, in turn, be eaten themselves. The trophic level of an organism is the number of steps it i ...


References


External links


Spatial heterogeneity of mesopredator release within an oceanic island system

Trophic cascades in a complex terrestrial community

Wolves drive trophic cascade in Banff National Park
{{modelling ecosystems, state=expanded Ecological theories Population dynamics Predation