Extinction threshold
Encyclopedia
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, 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 then extinction rate, otherwise the entire entity will go extinct once it reaches the threshold.
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. Modeling extinction thresholds can explain the relationship between extinction threshold and habitat loss and habitat fragmentation
.
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. When determining an extinction threshold there are two types of models that can be used: deterministic and stochastic metapopulation models.
dp/dt = chp (1-p)-ep
Where p= occupied patches , e= extinction rate, c= colonization rate, and h= amount of habitat.
A species will persist only if h> δ
where δ=e/c
δ= species parameter, or how successful a species is in colonizing a patch.
The complex nature of these models can result in a small metapopulation that is considered to be above the deterministic extinction threshold, but in reality has a high risk of extinction .
explained with an empirical example that when factors such as Allee effect
or Rescue effect were included in modeling the extinction threshold, there were unexpected extinctions in a high number of species. A more complex model came up with different results, and in practicing conservation biology this can add more confusion to efforts to save a species from the extinction threshold. Transient dynamics, which are effects on the extinction threshold because of instability in either the metapopulation or environmental conditions, is also a large player in modeling results. Landscapes that have recently endured habitat loss and fragmentation may be less able to sustain a metapopulation than previously understood without considering transient dynamics. Finally, environmental stochasticity, which may be spatially correlated, can lead to amplified regional stochastic fluctuations and therefore greatly affect the extinction risk.
Conservation biology
Conservation biology is the scientific study of the nature and status of Earth's biodiversity with the aim of protecting species, their habitats, and ecosystems from excessive rates of extinction...
to explain the point at which a species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
, population
Population
A population is all the organisms that both belong to the same group or species and live in the same geographical area. The area that is used to define a sexual population is such that inter-breeding is possible between any pair within the area and more probable than cross-breeding with individuals...
or metapopulation
Metapopulation
A metapopulation consists of a group of spatially separated populations of the same species which interact at some level. The term metapopulation was coined by Richard Levins in 1970 to describe a model of population dynamics of insect pests in agricultural fields, but the idea has been most...
, 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, though this may take a long time for species just below the critical value, a phenomenon known as extinction debt
Extinction debt
Extinction debt is a concept in ecology that describes the future extinction of species due to events in the past. Extinction debt occurs because of time delays between impacts on a species, such as destruction of habitat, and the species' ultimate disappearance...
.
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 then extinction rate, otherwise the entire entity will go extinct once it reaches the threshold.
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. Modeling extinction thresholds can explain the relationship between extinction threshold and habitat loss and habitat fragmentation
Habitat fragmentation
Habitat fragmentation as the name implies, describes the emergence of discontinuities in an organism's preferred environment , causing population fragmentation...
.
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 LevinsRichard Levins
Richard "Dick" Levins is a mathematical ecologist, and political activist. He is best known for his work on evolution in changing environments....
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
Russell Lande
Russell Lande is an American evolutionary biologist and ecologist, and a Royal Society Research Professor at Imperial College London, in Silwood Park.-Education and career:...
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. When determining an extinction threshold there are two types of models that can be used: deterministic and stochastic metapopulation models.
Deterministic
Deterministic metapopulation models assume that there are an infinite number of habitat patches available and predict that the metapopulation will go extinct only if the threshold is not met.dp/dt = chp (1-p)-ep
Where p= occupied patches , e= extinction rate, c= colonization rate, and h= amount of habitat.
A species will persist only if h> δ
where δ=e/c
δ= species parameter, or how successful a species is in colonizing a patch.
Stochastic
Stochastic metapopulation models take into account stochasticity, which is the non-deterministic or random processes in nature. With this approach a metapopulation may be above the threshold if determined that it is unlikely it will go extinct within a certain time period.The complex nature of these models can result in a small metapopulation that is considered to be above the deterministic extinction threshold, but in reality has a high risk of extinction .
Other Factors
When using metapopulation-type models to predict extinction thresholds there are a number of factors that can affect the results of a model. First, including more complicated models, rather than relying solely on the Levins model produces different dynamics. For example, in an article published in 2004, Otso Ovaskainen and Ilkka HanskiIlkka Hanski
Ilkka A. Hanski FRS is a Finnish scientist, working in the field of ecology, at Helsinki University, Finland. The Metapopulation Research Group led by Hanski has been nominated as a Center of Excellence by the Academy of Finland...
explained with an empirical example that when factors such as Allee effect
Allee effect
The Allee effect is a phenomenon in biology characterized by a positive correlation between population density and the per capita population growth rate in very small populations.-Description:...
or Rescue effect were included in modeling the extinction threshold, there were unexpected extinctions in a high number of species. A more complex model came up with different results, and in practicing conservation biology this can add more confusion to efforts to save a species from the extinction threshold. Transient dynamics, which are effects on the extinction threshold because of instability in either the metapopulation or environmental conditions, is also a large player in modeling results. Landscapes that have recently endured habitat loss and fragmentation may be less able to sustain a metapopulation than previously understood without considering transient dynamics. Finally, environmental stochasticity, which may be spatially correlated, can lead to amplified regional stochastic fluctuations and therefore greatly affect the extinction risk.
See also
- extinctionExtinctionIn biology and ecology, extinction is the end of an organism or of a group of organisms , normally 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 recover may have been lost before this point...
- habitat fragmentationHabitat fragmentationHabitat fragmentation as the name implies, describes the emergence of discontinuities in an organism's preferred environment , causing population fragmentation...
- ecological extinctionEcological extinctionEcological extinction is defined as “the reduction of a species to such low abundance that, although it is still present in the community, it no longer interacts significantly with other species.”...
- extinction vortexExtinction VortexExtinction vortices are a class of models through which conservation biologists, geneticists and ecologists can understand the dynamics of and categorize extinctions in the context of their causes. Developed by M. E. Gilpin and M. E...
- small population sizeSmall population sizeSmall populations behave differently from larger populations. They often result in population bottlenecks, which have harmful consequences for the survival of that population.-Demographic effects:...
- population geneticsPopulation geneticsPopulation genetics is the study of allele frequency distribution and change under the influence of the four main evolutionary processes: natural selection, genetic drift, mutation and gene flow. It also takes into account the factors of recombination, population subdivision and population...
- endangered speciesEndangered speciesAn endangered species is a population of organisms which is at risk of becoming extinct because it is either few in numbers, or threatened by changing environmental or predation parameters...
- wildlife conservationWildlife conservationWildlife conservation is the preservation, protection, or restoration of wildlife and their environment, especially in relation to endangered and vulnerable species. All living non-domesticated animals, even if bred, hatched or born in captivity, are considered wild animals. Wildlife represents all...
- environmentalismEnvironmentalismEnvironmentalism is a broad philosophy, ideology and social movement regarding concerns for environmental conservation and improvement of the health of the environment, particularly as the measure for this health seeks to incorporate the concerns of non-human elements...
- ecological thresholdEcological thresholdEcological threshold can be described as the point at which a relatively small change in external conditions causes a rapid change in an ecosystem. When an ecological threshold has been passed, the ecosystem may no longer be able to return to its state...
External links
- http://www.k-state.edu/withlab/publications/With&King1999b.pdf
- http://www.helsinki.fi/~ihanski/Articles/AnnZool%202003%20Ovaskainen%20&%20Hanski.pdf
- http://www.ese.u-psud.fr/epc/conservation/PDFs/Thresholds.pdf
- http://www.princeton.edu/~keymer/Teaching/EEB324/AmNat2000.pdf
- http://www.peripatus.gen.nz/paleontology/extinction.html
- http://www.helsinki.fi/~ihanski/