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Extinction threshold
Extinction threshold is a term used in conservation biology to explain the point at which a species, population or metapopulation, experiences an abrupt change in density or number because of an important parameter, such as habitat loss. It is at this critical value below which a species, population, or metapopulation, will go extinct,〔Ovaskainen, O. and Hanski, I. 2003:Extinction Threshold in Metapopulation Models, Ann.Zool.Fennic.40:81-97.〕 though this may take a long time for species just below the critical value, a phenomenon known as extinction debt.
Extinction thresholds are important to conservation biologists when studying a species in a population or metapopulation context because the colonization rate must be larger than the extinction rate, otherwise the entire entity will go extinct once it reaches the threshold.〔Groom, M., Meffe, G. K., and Carroll, C.R. 2000:Principles of Conservation Biology, 3rd Ed, Sinauer Associates.〕
Extinction thresholds are realized under a number of circumstances and the point in modeling them is to define the conditions that lead a population to extinction.〔With, K.A. and King, A.W. 1999:Extinction Thresholds For Species in Fractal Landscapes, Conservation Biology: Vol 13, No.2,pp.314-326.〕 Modeling extinction thresholds can explain the relationship between extinction threshold and habitat loss and habitat fragmentation.〔Fahrig, Lenore. 2002:Effect of Habitat Fragmentation on the Extinction Threshold: A Synthesis, Ecological Applications: Vol.12, No.2, pp.346-353.〕
== Mathematical models ==
Metapopulation-type models are used to predict extinction thresholds. The classic metapopulation model is the Levins Model, which is the model of metapopulation dynamics established by Richard Levins in the 1960s. It was used to evaluate patch occupancy in a large network of patches. This model was extended in the 1980s by Russell Lande to include habitat occupancy.〔 This mathematical model is used to infer the extinction values and important population densities. These mathematical models are primarily used to study extinction thresholds because of the difficulty in understanding extinction processes through empirical methods and the current lack of research on this subject.〔Deredec, A. and Courchamp,F, 2003:Extinction Thresholds in Host-Parasite Dynamics, Ann. Zool. Fennic. 40:115-130.〕 When determining an extinction threshold there are two types of models that can be used: deterministic and stochastic metapopulation models.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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