Mesopredator release hypothesis: Difference between revisions

The '''mesopredator release hypothesis''' is an [[ecology|ecological]] theory used to describe the interrelated [[population dynamics]] between [[apex predator]]s and [[mesopredator]]s within an [[ecosystem]], such that a collapsing population of the former results in dramatically-increased populations of the latter. This hypothesis describes the phenomenon of [[trophic cascade]] in specific terrestrial [[ecological community|communities]].

A mesopredator is a medium-sized, middle [[trophic level]] predator, which both predates and is predated upon. Examples are [[raccoon]]s, [[skunk]]s,<ref>{{IUCN2015.2|assessor=Reid, F.|assessor2=Helgen, K.|last-assessor-amp=yes|year=2008|id=41635|title=Mephitis mephitis|downloaded=22 September 2015}}</ref> [[snake]]s, [[cownose ray]]s, and small sharks.

The term "mesopredator release" was first used by Soulé and colleagues in 1988 to describe a process whereby mid-sized [[carnivorous]] 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]] species, such as birds.<ref name="Mesopredator">{{cite journal |first1=L.R. |last1=Prugh |first2=C.J. |last2=Stoner |first3=C.W. |last3=Epps |first4=W.T. |last4=Bean |first5=W.J. |last5=Ripple |first6=A.S. |last6=LaLiberte |first7=J.S. |last7=Brashares |title=The Rise of the Mesopredator |url=http://www.cof.orst.edu/leopold/papers/mesopredators.pdf |format=PDF |journal=BioScience |accessdate=22 September 2015 |volume=59 |issue=9 |pages=779–791 |date=October 2009 |issn=0006-3568 |doi=10.1525/bio.2009.59.9.9}}</ref><ref name="Sanicola 2007">{{cite web |last1=Sanicola |first1=S. |date=2007 |title=Mesopredator Release |url= http://www38.homepage.villanova.edu/jameson.chace/Urban%20Ecology/sanicole_files/v3_document.htm |accessdate=23 May 2007}}</ref><ref name="Courchamp et al. 1999">{{cite journal | last1 = Courchamp | first1 = F. | last2 = Langlais | first2 = M. | last3 = Sugihara | first3 = G. | year = 1999 | title = Cats protecting birds: modelling the mesopredator release effect | url = | journal = Journal of Animal Ecology | volume = 68 | issue = | pages = 282–292 | doi=10.1046/j.1365-2656.1999.00285.x}}</ref> This may lead to dramatic prey population decline, or even extinction, especially on islands. This process arises when mammalian top predators are considered to be the most influential factor on [[trophic level|trophic]] structure and [[biodiversity]] in terrestrial ecosystems.<ref name="Hebblewhite et al. 2005">{{Cite journal |last1=Hebblewhite |first1=M |last2=White |first2=CA |last3=Nietvelt |first3=CG |last4=McKenzie |first4=JA |last5=Hurd |first5=TE |last6=Fryxell |first6=JM |year=2005 |title=Human activity mediates a trophic cascade caused by wolves |journal=Ecology |volume=86 |issue=8 |pages=2135–2144 |url=http://scholarworks.umt.edu/cgi/viewcontent.cgi?article=1291&context=biosci_pubs |accessdate=22 September 2015 |format=PDF |doi=10.1890/04-1269}}</ref> Top predators may feed on herbivores and kill predators in lower [[trophic level]]s as well.<ref name="Palomares and Caro, 1999">{{cite journal | last1 = Palomares | first1 = E. | last2 = Caro | first2 = T.M. | year = 1999 | title = Interspecific killing among mammalian carnivores | url = | journal = Am. Nat. | volume = 153 | issue = | pages = 492–508 | doi=10.1086/303189}}</ref> 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.<ref name="Crooks and Soule, 1999">{{cite journal | last1 = Crooks | first1 = K.R. | last2 = Soulé | first2 = M.E. | year = 1999 | title = Mesopredator release and avifaunal extinctions in a fragmented system | url = | journal = Nature | volume = 400 | issue = | pages = 563–566 | doi=10.1038/23028}}</ref> The mesopredator release hypothesis offers an explanation for the abnormally high numbers of mesopredators and the decline in prey abundance and diversity.<ref name="Terborgh et al. 1999">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</ref> The hypothesis supports the argument for conservation of top predators because they protect smaller prey species that are in danger of extinction.<ref name = "Sanicola 2007"/> This argument has been a subject of interest within [[conservation biology]] for years, but few studies have adequately documented the phenomenon.<ref name="Elmhagen and Rushton, 2007">{{cite journal | last1 = Elmhagen | first1 = B. | last2 = Rushton | first2 = S. | year = 2007 | title = Trophic control of mesopredators in terrestrial ecosystems: top-down or bottom-up? | url = | journal = Ecology Letters | volume = 10 | issue = 3| pages = 197–206 | doi=10.1111/j.1461-0248.2006.01010.x}}</ref>

One of the main criticisms of the mesopredator release hypothesis is that it argues in favor of the [[top-down#Ecology|top-down control]] concept and excludes the possible impacts that bottom-up control could have on higher [[trophic level]]s.<ref name = "Elmhagen and Rushton, 2007"/> This means that it supports the argument that top predators control the structure and [[population dynamics]] 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.<ref name="Mesopredator" /> Another problem is that the hypothesis is offered as an explanation after large predators have already become rare or [[extinct]] in an ecosystem. Consequently, there is no data on the past ecosystem structure and the hypothesis cannot be tested.<ref name="Saether, 1999">{{cite journal | last1 = Sæther | first1 = B.E. | year = 1999 | title = Top dogs maintain diversity | url = | journal = Nature | volume = 400 | issue = | pages = 510–511 | doi=10.1038/22889}}</ref> 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]].<ref name="Bergstrom et al, 2009">{{cite journal | last1 = Bergstrom | first1 = D.M. | last2 = Lucieer | first2 = A. | last3 = Kiefer | first3 = K. | last4 = Wasely | first4 = J. | last5 = Belbin | first5 = L. | last6 = Pedersen | first6 = T.K. | last7 = Chown | first7 = S.L. | year = 2009 | title = Indirect effects of invasive species removal devastate world heritage island | url = | journal = Journal of Applied Ecology | volume = 46 | issue = | pages = 73–81 | doi=10.1111/j.1365-2664.2008.01601.x}}</ref>

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.<ref name="Lariviere, 2004">{{cite journal | last1 = Larivière | first1 = S | year = 2004 | title = Range expansion of raccoons in the Canadian prairies: review of hypotheses | url = | journal = Wildl. Soc. Bull | volume = 32 | issue = | pages = 955–963 | doi=10.2193/0091-7648(2004)032[0955:reorit]2.0.co;2}}</ref> Possible bottom-up effects on an ecosystem can be from [[bioclimatic]] impacts on ecosystem productivity and from anthropogenic habitat alterations.<ref name = "Elmhagen and Rushton, 2007"/> 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]]. It also does not mention that trophic interactions operate at different strengths according to the ecosystem.<ref name="Oksanen and Oksanen, 2000">{{cite journal | last1 = Oksanen | first1 = L. | last2 = Oksanen | first2 = T. | year = 2000 | title = The logic and realism of the hypothesis of exploitation ecosystems | url = | journal = Am. Nat. | volume = 155 | issue = | pages = 703–723 | doi=10.1086/303354}}</ref> Therefore, the roles of predation and food/nutrient processes in influencing ecosystem structures remain open to controversy and further testing.<ref name="Pace et al. 1999">{{cite journal | last1 = Pace | first1 = M.L. | last2 = Cole | first2 = J.J. | last3 = Carpenter | first3 = S.R. | last4 = Kitchell | first4 = J.F. | year = 1999 | title = Trophic cascades revealed in diverse ecosystems | url = | journal = Trends Ecol. Evol. | volume = 14 | issue = | pages = 483–488 | doi=10.1016/s0169-5347(99)01723-1 | pmid=10542455}}</ref>