Extinction debt
Encyclopedia
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. For instance, long-lived trees may survive for many years even after reproduction of new trees has become impossible, and thus they may be committed to extinction. Technically, extinction debt generally refers to the number of species in an area likely to go extinct, rather than the prospects of any one species, but colloquially it refers to any occurrence of delayed extinction.
In discussions of threats to biodiversity, extinction debt is analogous to the "climate commitment" in climate change
, which states that inertia
will cause the earth to continue to warm for centuries even if no more greenhouse gasses are emitted. Similarly, the current extinction may continue long after human impacts on species halt.
Extinction debt may be local or global, but most examples are local as these are easier to observe and model. It is most likely to be found in long-lived species and species with very specific habitat requirements (specialists). Extinction debt has important implications for conservation, as it implies that species may go extinct due to past habitat destruction, even if continued impacts cease, and that current reserves may not be sufficient to maintain the species that occupy them. Interventions such as habitat restoration may reverse extinction debt.
Immigration credit is the corollary to extinction debt. It refers to the number of species likely to immigrate to an area after an event such as the restoration of an ecosystem
.
. The most well-known drivers of extinction debt are habitat fragmentation
and habitat destruction
. These cause extinction debt by reducing the ability of species to persist via immigration to new habitats. Under equilibrium
conditions, species may go extinct in one habitat patch, yet continues to survive because it can disperse
to other patches. However, as other patches have been destroyed or rendered inaccessible due to fragmentation, this "insurance" effect is reduced and the species may ultimately go extinct.
Pollution
may also cause extinction debt by reducing a species' birth rate
or increasing its death rate so that its population slowly declines. Extinction debts may be caused by invasive species
or by climate change
.
Extinction debt may also occur due to the loss of mutualist species. In New Zealand, the local extinction of several species of pollinating birds in 1870 has caused a long-term reduction in the reproduction of the shrub species Rhabdothamnus solandri, which requires these birds to produce seeds. However, as the plant is slow-growing and long-lived, its populations persist.
10,000 years ago still appear to be losing species as a result. It has been shown that some bryozoa
ns, a type of microscopic marine organism, went extinct due to the volcanic
rise of the Isthmus of Panama
. This event cut off the flow of nutrients from the Pacific Ocean
to the Caribbean
3-4.5 million years ago. While bryozoan populations dropped severely at this time, extinction of these species took another 1-2 million years.
Extinction debts incurred due to human actions have shorter timescales. Local extinction of birds from rainforest fragmentation occurs over years or decades, while plants in fragmented grasslands show debts lasting 50 to 100 years. Tree species in fragmented temperate forests have debts lasting 200 years or more.
used the term "relaxation time" to describe a similar phenomenon in 1972. Tilman et al. demonstrated that extinction debt could occur using a mathematical model
of species metapopulations. Metapopulations are multiple populations of a species that live in separate habitat patches or islands but interact via immigration between the patches. In this model, species persist via a balance between random local extinctions in patches and colonization
of new patches. Tilman et al. al used this model to predict that species would persist long after they no longer had sufficient habitat to support them. When used to estimate extinction debts of tropical tree species, the model predicted debts lasting 50–400 years.
One of the assumptions underlying the original extinction debt model was a trade-off between species' competitive
ability and colonization ability. That is, a species that competes well against other species, and is more likely to become dominant in an area, is less likely to colonize new habitats due to evolutionary trade-offs . One of the implications of this assumption is that better competitors, which may even be more common than other species, are more likely to go extinct than rarer, less competitive, better dispersing species. This has been one of the more controversial components of the model, as there is little evidence for this trade-off in many ecosystems, and in many empirical studies dominant competitors were least likely species to go extinct. A later modification of the model showed that these trade-off assumptions may be relaxed, but need to exist partially, in order for the theory to work.
, or random fluctuation in populations, show extinction debt occurring over different time scales than classic models.
Most recently, extinction debts have been estimated through the use models derived from neutral theory
. Neutral theory has very different assumptions than the metapopulation models described above. It predicts that the abundance and distribution of species can be predicted entirely through random processes, without considering the traits of individual species. As extinction debt arises in models under such different assumptions, it is robust to different kinds of models. Models derived from neutral theory have successfully predicted extinction times for a number of bird species, but perform poorly at both very small and very large spatial scales.
Mathematical models have also shown that extinction debt will last longer if it occurs in response to large habitat impacts (as the system will move farther from equilibrium), and if species are long-lived. Also, species just below their extinction threshold
, that is, just below the population level or habitat occupancy levels required sustain their population, will have long-term extinction debts. Finally, extinction debts are predicted to last longer in landscapes with a few large patches of habitat, rather than many small ones.
of insects living on moss habitats demonstrated that extinction debt occurs after habitat destruction. In these experiments, it took 6–12 months for species to die out following the destruction of habitat.
If one has information on species populations from the past in addition to the present, the magnitude of extinction debt can be estimated. One can use the relationshop between species and habitat from the past to predict the number of species expected in the present. The difference between this estimate and the actual number of species is the extinction debt.
This method requires the assumption that that in the past species and their habitat were in equilibrium
, which is often unknown. Also, a common relationship used to equate habitat and species number is the species-area curve
, but as the species-area curve arises from very different mechanisms than those in metapopulation
based models, extinction debts measured in this way may not conform with metapopulation models' predictions. The relationship between habitat and species number can also be represented by much more complex models that simulate the behavior of many species independently.
appears to be a remnant of more connected landscapes present 50 to 100 years ago. In alvar grasslands
in Estonia
that have lost area since the 1930s, 17-70% of species are estimated to be committed to extinction. However, studies of similar grasslands in Belgium
, where similar impacts have occurred, show no evidence of extinction debt. This may be due to differences in the scale of measurement or the level of specialization of grass species.
that occurred between 1775 and 1900. Detailed modeling of species behavior, based on similar forests in England
that did not experience deforestation, showed that long-lived and slow-growing species were more common than equilibrium models would predict, indicating that their presence was due to lingering extinction debt.
In Sweden, some species of lichens show an extinction debt in fragments of ancient forest. However, species of lichens that are habitat generalists, rather than specialists, do not.
and Muhu
- islands off the western coast of Estonia. Butterfly species distributions on these islands are better explained by the habitat in the past than current habitats.
On the islands of the Azores
Archipelago
, more than 95% of native forests have been destroyed in the past 600 years. As a result, more than half of arthropods on these islands are believed to be committed to extinction, with many islands likely to lose more than 90% of species.
than are thought to be able to be supported by current nature reserves.
Birds in the Amazon rain forest continued to go extinct locally for 12 years following logging that broke up contiguous forest into smaller fragments. The extinction rate slowed, however, as forest regrew in the spaces in between habitat fragments.
are estimated to have, on average, a local extinction debt of 30% for forest-dwelling primates. That is, they are expected to have 30% of their forest primate species to go extinct in the future due to loss of forest habitat
. The time scale for these extinctions has not been estimated.
. It implies that in the absence of further habitat destruction or other environmental impacts, many species are still likely to go extinct. Protection of existing habitats may not be sufficient to protect species from extinction. However, the long time scales of extinction debt may allow for habitat restoration
in order to prevent extinction, as occurred in the slowing of extinction in Amazon forest birds above. In another example, it has been found that grizzly bears in very small reserves in the Rocky Mountains
are likely to go extinct, but this finding allows the modification of reserve networks to better support their populations.
The extinction debt concept may require revision of the value of land for species conservation, as the number of species currently present in a habitat may not be a good measure of the habitat's ability to support species (see carrying capacity
) in the future. As extinction debt may last longest near extinction thresholds, it may be hardest to detect the threat of extinction in for species that conservation could the most.
Economic analyses have shown that including extinction in management decision-making process changes decision outcomes, as the decision to destroy habitat changes conservation value in the future as well as the present. It is estimated that in Costa Rica
, ongoing extinction debt may cost between $88 million and $467 million.
Ecology
Ecology is the scientific study of the relations that living organisms have with respect to each other and their natural environment. Variables of interest to ecologists include the composition, distribution, amount , number, and changing states of organisms within and among ecosystems...
that describes the future extinction
Extinction
In 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...
of 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...
due to events in the past. Extinction debt occurs because of time delays between impacts on a species, such as destruction of habitat
Habitat
* Habitat , a place where a species lives and grows*Human habitat, a place where humans live, work or play** Space habitat, a space station intended as a permanent settlement...
, and the species' ultimate disappearance. For instance, long-lived trees may survive for many years even after reproduction of new trees has become impossible, and thus they may be committed to extinction. Technically, extinction debt generally refers to the number of species in an area likely to go extinct, rather than the prospects of any one species, but colloquially it refers to any occurrence of delayed extinction.
In discussions of threats to biodiversity, extinction debt is analogous to the "climate commitment" in climate change
Climate change
Climate change is a significant and lasting change in the statistical distribution of weather patterns over periods ranging from decades to millions of years. It may be a change in average weather conditions or the distribution of events around that average...
, which states that inertia
Inertia
Inertia is the resistance of any physical object to a change in its state of motion or rest, or the tendency of an object to resist any change in its motion. It is proportional to an object's mass. The principle of inertia is one of the fundamental principles of classical physics which are used to...
will cause the earth to continue to warm for centuries even if no more greenhouse gasses are emitted. Similarly, the current extinction may continue long after human impacts on species halt.
Extinction debt may be local or global, but most examples are local as these are easier to observe and model. It is most likely to be found in long-lived species and species with very specific habitat requirements (specialists). Extinction debt has important implications for conservation, as it implies that species may go extinct due to past habitat destruction, even if continued impacts cease, and that current reserves may not be sufficient to maintain the species that occupy them. Interventions such as habitat restoration may reverse extinction debt.
Immigration credit is the corollary to extinction debt. It refers to the number of species likely to immigrate to an area after an event such as the restoration of an ecosystem
Ecosystem restoration
Ecosystem restoration is the return of a damaged ecological system to a stable, healthy, and sustainable state, often together with associated ecosystem services-Rationale:There are many reasons to restore ecosystems. Some include:...
.
Causes
Extinction debt is caused by many of the same drivers as extinctionExtinction
In 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...
. The most well-known drivers of extinction debt are habitat fragmentation
Habitat fragmentation
Habitat fragmentation as the name implies, describes the emergence of discontinuities in an organism's preferred environment , causing population fragmentation...
and habitat destruction
Habitat destruction
Habitat destruction is the process in which natural habitat is rendered functionally unable to support the species present. In this process, the organisms that previously used the site are displaced or destroyed, reducing biodiversity. Habitat destruction by human activity mainly for the purpose of...
. These cause extinction debt by reducing the ability of species to persist via immigration to new habitats. Under equilibrium
Equilibrium
Equilibrium is the condition of a system in which competing influences are balanced. The word may refer to:-Biology:* Equilibrioception, the sense of a balance present in human beings and other animals...
conditions, species may go extinct in one habitat patch, yet continues to survive because it can disperse
Biological dispersal
Biological dispersal refers to species movement away from an existing population or away from the parent organism. Through simply moving from one habitat patch to another, the dispersal of an individual has consequences not only for individual fitness, but also for population dynamics, population...
to other patches. However, as other patches have been destroyed or rendered inaccessible due to fragmentation, this "insurance" effect is reduced and the species may ultimately go extinct.
Pollution
Pollution
Pollution is the introduction of contaminants into a natural environment that causes instability, disorder, harm or discomfort to the ecosystem i.e. physical systems or living organisms. Pollution can take the form of chemical substances or energy, such as noise, heat or light...
may also cause extinction debt by reducing a species' birth rate
Birth rate
Crude birth rate is the nativity or childbirths per 1,000 people per year . Another word used interchangeably with "birth rate" is "natality". When the crude birth rate is subtracted from the crude death rate, it reveals the rate of natural increase...
or increasing its death rate so that its population slowly declines. Extinction debts may be caused by invasive species
Invasive species
"Invasive species", or invasive exotics, is a nomenclature term and categorization phrase used for flora and fauna, and for specific restoration-preservation processes in native habitats, with several definitions....
or by climate change
Climate change
Climate change is a significant and lasting change in the statistical distribution of weather patterns over periods ranging from decades to millions of years. It may be a change in average weather conditions or the distribution of events around that average...
.
Extinction debt may also occur due to the loss of mutualist species. In New Zealand, the local extinction of several species of pollinating birds in 1870 has caused a long-term reduction in the reproduction of the shrub species Rhabdothamnus solandri, which requires these birds to produce seeds. However, as the plant is slow-growing and long-lived, its populations persist.
Time scale
The time to "payoff" of extinction debt can be very long. Islands that lost habitat at the end of the last ice ageIce age
An ice age or, more precisely, glacial age, is a generic geological period of long-term reduction in the temperature of the Earth's surface and atmosphere, resulting in the presence or expansion of continental ice sheets, polar ice sheets and alpine glaciers...
10,000 years ago still appear to be losing species as a result. It has been shown that some bryozoa
Bryozoa
The Bryozoa, also known as Ectoprocta or commonly as moss animals, are a phylum of aquatic invertebrate animals. Typically about long, they are filter feeders that sieve food particles out of the water using a retractable lophophore, a "crown" of tentacles lined with cilia...
ns, a type of microscopic marine organism, went extinct due to the volcanic
Volcano
2. Bedrock3. Conduit 4. Base5. Sill6. Dike7. Layers of ash emitted by the volcano8. Flank| 9. Layers of lava emitted by the volcano10. Throat11. Parasitic cone12. Lava flow13. Vent14. Crater15...
rise of the Isthmus of Panama
Isthmus of Panama
The Isthmus of Panama, also historically known as the Isthmus of Darien, is the narrow strip of land that lies between the Caribbean Sea and the Pacific Ocean, linking North and South America. It contains the country of Panama and the Panama Canal...
. This event cut off the flow of nutrients from the Pacific Ocean
Pacific Ocean
The Pacific Ocean is the largest of the Earth's oceanic divisions. It extends from the Arctic in the north to the Southern Ocean in the south, bounded by Asia and Australia in the west, and the Americas in the east.At 165.2 million square kilometres in area, this largest division of the World...
to the Caribbean
Caribbean
The Caribbean is a crescent-shaped group of islands more than 2,000 miles long separating the Gulf of Mexico and the Caribbean Sea, to the west and south, from the Atlantic Ocean, to the east and north...
3-4.5 million years ago. While bryozoan populations dropped severely at this time, extinction of these species took another 1-2 million years.
Extinction debts incurred due to human actions have shorter timescales. Local extinction of birds from rainforest fragmentation occurs over years or decades, while plants in fragmented grasslands show debts lasting 50 to 100 years. Tree species in fragmented temperate forests have debts lasting 200 years or more.
Origins in metapopulation models
The term "extinction debt" was first used in 1994 in a paper by David Tilman et al., though Jared DiamondJared Diamond
Jared Mason Diamond is an American scientist and author whose work draws from a variety of fields. He is currently Professor of Geography and Physiology at UCLA...
used the term "relaxation time" to describe a similar phenomenon in 1972. Tilman et al. demonstrated that extinction debt could occur using a mathematical model
Ecosystem model
An ecosystem model is an abstract, usually mathematical, representation of an ecological system , which is studied to gain a deeper understanding of the real system.Ecosystem models are formed by combining known ecological relations An ecosystem model is an abstract, usually mathematical,...
of species metapopulations. Metapopulations are multiple populations of a species that live in separate habitat patches or islands but interact via immigration between the patches. In this model, species persist via a balance between random local extinctions in patches and colonization
Colonisation (biology)
Colonisation is the process in biology by which a species spreads into new areas, regions, and continents. It is sometimes also referred to as immigration, but colonisation often refers to successful immigration with integration to a community, having resisted initial local extinction.One classic...
of new patches. Tilman et al. al used this model to predict that species would persist long after they no longer had sufficient habitat to support them. When used to estimate extinction debts of tropical tree species, the model predicted debts lasting 50–400 years.
One of the assumptions underlying the original extinction debt model was a trade-off between species' competitive
Competition (biology)
Competition is an interaction between organisms or species, in which the fitness of one is lowered by the presence of another. Limited supply of at least one resource used by both is required. Competition both within and between species is an important topic in ecology, especially community ecology...
ability and colonization ability. That is, a species that competes well against other species, and is more likely to become dominant in an area, is less likely to colonize new habitats due to evolutionary trade-offs . One of the implications of this assumption is that better competitors, which may even be more common than other species, are more likely to go extinct than rarer, less competitive, better dispersing species. This has been one of the more controversial components of the model, as there is little evidence for this trade-off in many ecosystems, and in many empirical studies dominant competitors were least likely species to go extinct. A later modification of the model showed that these trade-off assumptions may be relaxed, but need to exist partially, in order for the theory to work.
Development in other models
Further theoretical work has shown that extinction debt can occur under many different circumstances, driven by different mechanisms and under different model assumptions. The original model predicted extinction debt as a result of habitat destruction in a system of small, isolated habitats such as islands. Later models showed that extinction debt could occur in systems where habitat destruction occurs in small areas within a large area of habitat, as in slash-and-burn agriculture in forests, and could also occur due to decreased growth of species from pollutants. Predicted patterns of extinction debt differ between models, though. For instance, habitat destruction resembling slash-and-burn agriculture is thought to affect rare species rather than poor colonizers. Models that incorporate stochasticityStochastic process
In probability theory, a stochastic process , or sometimes random process, is the counterpart to a deterministic process...
, or random fluctuation in populations, show extinction debt occurring over different time scales than classic models.
Most recently, extinction debts have been estimated through the use models derived from neutral theory
Unified neutral theory of biodiversity
The unified neutral theory of biodiversity and biogeography is a hypothesis and the title of a monograph by ecologist Stephen Hubbell...
. Neutral theory has very different assumptions than the metapopulation models described above. It predicts that the abundance and distribution of species can be predicted entirely through random processes, without considering the traits of individual species. As extinction debt arises in models under such different assumptions, it is robust to different kinds of models. Models derived from neutral theory have successfully predicted extinction times for a number of bird species, but perform poorly at both very small and very large spatial scales.
Mathematical models have also shown that extinction debt will last longer if it occurs in response to large habitat impacts (as the system will move farther from equilibrium), and if species are long-lived. Also, species just below their extinction threshold
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...
, that is, just below the population level or habitat occupancy levels required sustain their population, will have long-term extinction debts. Finally, extinction debts are predicted to last longer in landscapes with a few large patches of habitat, rather than many small ones.
Detection
Extinction debt is difficult to detect and measure. Processes that drive extinction debt are inherently slow and highly variable (noisy), and it is difficult to locate or count the very small populations of near-extinct species. Because of these issues, most measures of extinction debt have a great deal of uncertainty.Experimental evidence
Due to the logistical and ethical difficulties of inciting extinction debt, there are few studies of extinction debt in controlled experiments. However, experiments microcosmsMicrocosm: Model / experimental ecosystem
Microcosms are artificial, simplified ecosystems that are used to simulate and predict the behaviour of natural ecosystems under controlled conditions. Open or closed microcosms provide an experimental area for ecologists to study natural ecological processes. Microcosm studies can be very useful...
of insects living on moss habitats demonstrated that extinction debt occurs after habitat destruction. In these experiments, it took 6–12 months for species to die out following the destruction of habitat.
Long-term observation
Extinction debts that reach equilibrium in relatively short time scales (years to decades) can be observed via measuring the change in species numbers in the time following an impact on habitat. For instance, in the Amazon forest, researchers have measured the rate at which bird species disappear after forest is cut down. As even short-term extinction debts can take years to decades to reach equilibrium, though, such studies take many years and good data are rare.Comparing the past and present
Most studies of extinction debt compare species numbers with habitat patterns from the past and habitat patterns in the present. If the present populations of species are more closely related to past habitat patterns than present, extinction debt is a likely explanation. The magnitude of extinction debt (i.e., number of species likely to go extinct) can not be estimated by this method.If one has information on species populations from the past in addition to the present, the magnitude of extinction debt can be estimated. One can use the relationshop between species and habitat from the past to predict the number of species expected in the present. The difference between this estimate and the actual number of species is the extinction debt.
This method requires the assumption that that in the past species and their habitat were in equilibrium
Equilibrium
Equilibrium is the condition of a system in which competing influences are balanced. The word may refer to:-Biology:* Equilibrioception, the sense of a balance present in human beings and other animals...
, which is often unknown. Also, a common relationship used to equate habitat and species number is the species-area curve
Species-area curve
In ecology, a species-area curve is a relationship between the area of a habitat, or of part of a habitat, and the number of species found within that area. Larger areas tend to contain larger numbers of species, and empirically, the relative numbers seem to follow systematic mathematical...
, but as the species-area curve arises from very different mechanisms than those in 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...
based models, extinction debts measured in this way may not conform with metapopulation models' predictions. The relationship between habitat and species number can also be represented by much more complex models that simulate the behavior of many species independently.
Comparing impacted and pristine habitats
If data on past species numbers or habitat are not available, species debt can also be estimated by comparing two different habitats: one which is mostly intact, and another which has had areas cleared and is smaller and more fragmented. One can then measure the relationship of species with the condition of habitat in the intact habitat, and, assuming this represents equilibrium, use it to predict the number of species in the cleared habitat. If this prediction is lower than the actual number of species in the cleared habitat, then the difference represents extinction debt. This method requires many of the same assumptions as methods comparing the past and present.Grasslands
Studies of European grasslands show evidence of extinction debt through both comparisons with the past and between present-day systems with different levels of human impacts. The species diversity of grasslands in SwedenSweden
Sweden , officially the Kingdom of Sweden , is a Nordic country on the Scandinavian Peninsula in Northern Europe. Sweden borders with Norway and Finland and is connected to Denmark by a bridge-tunnel across the Öresund....
appears to be a remnant of more connected landscapes present 50 to 100 years ago. In alvar grasslands
Alvar
An alvar is a biological environment based on a limestone plain with thin or no soil and, as a result, sparse vegetation. It is also known as a pavement barren although this term is also used for similar landforms based on sandstone. In the United Kingdom the exposed landform is called a limestone...
in Estonia
Estonia
Estonia , officially the Republic of Estonia , is a state in the Baltic region of Northern Europe. It is bordered to the north by the Gulf of Finland, to the west by the Baltic Sea, to the south by Latvia , and to the east by Lake Peipsi and the Russian Federation . Across the Baltic Sea lies...
that have lost area since the 1930s, 17-70% of species are estimated to be committed to extinction. However, studies of similar grasslands in Belgium
Belgium
Belgium , officially the Kingdom of Belgium, is a federal state in Western Europe. It is a founding member of the European Union and hosts the EU's headquarters, and those of several other major international organisations such as NATO.Belgium is also a member of, or affiliated to, many...
, where similar impacts have occurred, show no evidence of extinction debt. This may be due to differences in the scale of measurement or the level of specialization of grass species.
Forests
Forests in Vlaams-Brabant, Belgium, show evidence of extinction debt remaining from deforestationDeforestation
Deforestation is the removal of a forest or stand of trees where the land is thereafter converted to a nonforest use. Examples of deforestation include conversion of forestland to farms, ranches, or urban use....
that occurred between 1775 and 1900. Detailed modeling of species behavior, based on similar forests in England
England
England is a country that is part of the United Kingdom. It shares land borders with Scotland to the north and Wales to the west; the Irish Sea is to the north west, the Celtic Sea to the south west, with the North Sea to the east and the English Channel to the south separating it from continental...
that did not experience deforestation, showed that long-lived and slow-growing species were more common than equilibrium models would predict, indicating that their presence was due to lingering extinction debt.
In Sweden, some species of lichens show an extinction debt in fragments of ancient forest. However, species of lichens that are habitat generalists, rather than specialists, do not.
Insects
Extinction debt has been found among species of butterflies living in the grasslands on SaaremaaSaaremaa
Saaremaa is the largest island in Estonia, measuring 2,673 km². The main island of Saare County, it is located in the Baltic Sea, south of Hiiumaa island, and belongs to the West Estonian Archipelago...
and Muhu
Muhu
Muhu , is an island in the Baltic Sea. With an area of 198 km² it is the third largest island belonging to Estonia, after Saaremaa and Hiiumaa....
- islands off the western coast of Estonia. Butterfly species distributions on these islands are better explained by the habitat in the past than current habitats.
On the islands of the Azores
Azores
The Archipelago of the Azores is composed of nine volcanic islands situated in the middle of the North Atlantic Ocean, and is located about west from Lisbon and about east from the east coast of North America. The islands, and their economic exclusion zone, form the Autonomous Region of the...
Archipelago
Archipelago
An archipelago , sometimes called an island group, is a chain or cluster of islands. The word archipelago is derived from the Greek ἄρχι- – arkhi- and πέλαγος – pélagos through the Italian arcipelago...
, more than 95% of native forests have been destroyed in the past 600 years. As a result, more than half of arthropods on these islands are believed to be committed to extinction, with many islands likely to lose more than 90% of species.
Birds
Based on historical species-area relationships, Hungary currently has approximately nine more species of raptorsBird of prey
Birds of prey are birds that hunt for food primarily on the wing, using their keen senses, especially vision. They are defined as birds that primarily hunt vertebrates, including other birds. Their talons and beaks tend to be relatively large, powerful and adapted for tearing and/or piercing flesh....
than are thought to be able to be supported by current nature reserves.
Birds in the Amazon rain forest continued to go extinct locally for 12 years following logging that broke up contiguous forest into smaller fragments. The extinction rate slowed, however, as forest regrew in the spaces in between habitat fragments.
Primates
Countries in AfricaAfrica
Africa is the world's second largest and second most populous continent, after Asia. At about 30.2 million km² including adjacent islands, it covers 6% of the Earth's total surface area and 20.4% of the total land area...
are estimated to have, on average, a local extinction debt of 30% for forest-dwelling primates. That is, they are expected to have 30% of their forest primate species to go extinct in the future due to loss of forest habitat
Habitat
* Habitat , a place where a species lives and grows*Human habitat, a place where humans live, work or play** Space habitat, a space station intended as a permanent settlement...
. The time scale for these extinctions has not been estimated.
Applications to conservation
The existence of extinction debt in many different ecosystems has important implications for conservationConservation 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...
. It implies that in the absence of further habitat destruction or other environmental impacts, many species are still likely to go extinct. Protection of existing habitats may not be sufficient to protect species from extinction. However, the long time scales of extinction debt may allow for habitat restoration
Restoration ecology
-Definition:Restoration ecology is the scientific study and practice of renewing and restoring degraded, damaged, or destroyed ecosystems and habitats in the environment by active human intervention and action, within a short time frame...
in order to prevent extinction, as occurred in the slowing of extinction in Amazon forest birds above. In another example, it has been found that grizzly bears in very small reserves in the Rocky Mountains
Rocky Mountains
The Rocky Mountains are a major mountain range in western North America. The Rocky Mountains stretch more than from the northernmost part of British Columbia, in western Canada, to New Mexico, in the southwestern United States...
are likely to go extinct, but this finding allows the modification of reserve networks to better support their populations.
The extinction debt concept may require revision of the value of land for species conservation, as the number of species currently present in a habitat may not be a good measure of the habitat's ability to support species (see carrying capacity
Carrying capacity
The carrying capacity of a biological species in an environment is the maximum population size of the species that the environment can sustain indefinitely, given the food, habitat, water and other necessities available in the environment...
) in the future. As extinction debt may last longest near extinction thresholds, it may be hardest to detect the threat of extinction in for species that conservation could the most.
Economic analyses have shown that including extinction in management decision-making process changes decision outcomes, as the decision to destroy habitat changes conservation value in the future as well as the present. It is estimated that in Costa Rica
Costa Rica
Costa Rica , officially the Republic of Costa Rica is a multilingual, multiethnic and multicultural country in Central America, bordered by Nicaragua to the north, Panama to the southeast, the Pacific Ocean to the west and the Caribbean Sea to the east....
, ongoing extinction debt may cost between $88 million and $467 million.