Types of Species Extinction of Species IUCN Red List
The species according to their role are divided as:
• Dominant species
These are species with substantially higher abundance or biomass than other species in a community. They exert a powerful control over the occurrence and distribution of other species. For example: Tidal swamps in the tropics are usually dominated by species of mangrove (Rhizophoraceae).
• Keystone species
These are species that is not necessarily abundant in a community yet exerts strong control on community structure by the nature of its ecological role or niche. A small number of keystone species can have a huge impact on the environment.
A keystone species’ disappearance would start a domino effect. Other species in the habitat would also disappear and become extinct. The keystone species’ disappearance could affect other species that rely on it for survival. For example, the population of deer or rabbits would explode without the presence of a predator. The ecosystem cannot support an unlimited number of animals, and the deer soon compete with each other for food and water resources. Their population usually declines without a predator such as a mountain lion.
• Foundation Species
Foundation species play a major role in creating or maintaining a habitat that supports other species. Corals are one example of a foundation species in many islands in the South Pacific Ocean.
Corals produce the reef structures on which countless other organisms, including human beings, live. Umbrella Species An umbrella species is a large animal or other organism on which many other species depend.
• Umbrella species
Umbrella species are very similar to keystone species, but umbrella species are usually migratory and need a large habitat.
Protection of umbrella species is thought to automatically protect a host of other species. Tigers are an example of an umbrella species. Efforts to save wild tigers in forests in the Indian state of Rajasthan also accomplish the goal of saving other species there, such as leopards, boars, hares, antelopes, and monkeys.
• Critical Link Species
They are species that play an important role in supporting network species as pollinators, dispersal agents, absorption or circulation of nutrients, etc. Mycorrhizal fungi help the vascular plants in obtaining inorganic nutrients from soil and organic residues.
• Flagship species
Flagship species are species that have the ability to capture the imagination of the public and induce people to support conservation action and/or to donate funds.
These are popular, charismatic species that serve as symbols and rallying points to stimulate conservation awareness and action.
Examples of flagship species include the Bengal tiger, the giant panda, Asian elephant (Elephas maximus), etc.
Flagship species can represent an environmental feature (e.g. a species or ecosystem), cause (e.g. climate change or ocean acidification), organization (e.g. NGO or government department) or geographic region (e.g. state or protected area).
• Indicator species
An indicator species is an organism whose presence, absence or abundance reflects a specific environmental condition.
Indicator species can signal a change in the biological condition of a particular ecosystem, and thus may be used as a proxy to diagnose the health of an ecosystem. For example, plants or lichens sensitive to heavy metals or acids in precipitation may be indicators of air pollution.
Indicator species can also reflect a unique set of environmental qualities or characteristics found in a specific place, such as a unique microclimate.
• Edge species
The species which are found abundantly in ecotone boundary are known as edge species.
Extinction of Species is a natural process. Species have disappeared and new ones have evolved to take their place over the long geological history of the earth. It is useful to distinguish three types of extinction processes.
Natural extinction: With the change in environmental conditions, some species disappear and others, which are more adapted to changed conditions, take their place. This loss of species which occurred in the geological past at a very slow rate is called natural or background extinction.
Mass extinction: There have been several periods in the earth’s geological history when large number of species became extinct because of catastrophes. Mass extinctions occur in millions of years.
Anthropogenic extinction: An increasing number of species is disappearing from the face of the earth due to the human activities. This man-made mass extinction represents a very severe depletion of biodiversity, particularly because it is occurring within a short period of time.
The vulnerability of a species to extinction depends on a wide variety of factors, some of which are:
i. Species with narrow geographical ranges: They may be threatened if human activity affects the whole range. Such locally endemic species are highly susceptible to extinction, although they can be saved by protecting a small area. For example, the heath hen, endemic to the Martha’s Vineyard Island in USA, became extinct due to local natural disasters.
ii. Species with only one or a few populations: They are highly vulnerable to even natural disasters like earthquakes or floods. Species with many populations are less vulnerable to global extinctions.
iii. Seasonal migratory species: They depend on two or more distinct habitat types, and are unable to survive if either habitat is destroyed. Barriers for movement between the habitats like roads, dams, electric lines etc., may also affect them adversely.
iv. Species with specialized niche requirements: Some species have highly specialized dietary requirements, or some, like wetland plants, may be very specific about environmental changes, like water level changes. Any disruption in these conditions can threaten such species.
v. Species that are not effective dispersers: Organisms, which poorly adapt to changing conditions, can survive if they have the ability to migrate to more favourable environments. Species that are unable to cross structures and disturbed habitats created by human activity face the threat of extinction.
vi. Species low in genetic variability: Adapting to new environments and changing conditions depend on the availability of genetic diversity.
vii. Species with small population sizes.
viii. Species in which the population is declining due to natural causes.
ix. Species with low population densities.
x. Species that need large home range, like the Bengal Tiger. Usually, large-sized animals require larger ranges.
xi. Species living in rather stable environments: Since.-disturbance is minimal, these species show very little adaptability and any large scale disruption of the environment can be dangerous for them.
xii. Species those are hunted and harvested by people.
IUCN Red List
The IUCN Red List is a rich compendium of information on threats, ecological requirements, and habitats of species; and on conservation actions that can be taken to reduce or prevent extinctions. It is based on an objective system for assessing the risk of extinction of a species based on past, present, and projected threats.
The IUCN Red List Index (RLI) reveals trends in the overall extinction risk of species and provides an indicator that is used by governments to track their progress in achieving targets that reduce biodiversity loss. The Red List Index has been adopted by the United Nations as one of the indicators for the 2015 Millennium Development Goal 7 on environmental sustainability.
The different categories of existing plants and animal species based on the International Union for Conservation of Nature and Natural Resources (IUCN) are –
• Extinct (EX)
A taxon is Extinct when there is no reasonable doubt that the last individual has died. A taxon is presumed extinct when exhaustive surveys in known and/or expected habitat, at appropriate tim es (diurnal, seasonal, annual), throughout its historic range have failed to record an individual. Surveys should be over a time frame appropriate to the taxon’s life cycle and life form.
• Extinct in the Wild (EW)
A taxon is Extinct in the Wild when it is known only to survive in cultivation, in captivity or as a naturalized population (or populations) well outside the past range. A taxon is presumed Extinct in the Wild when exhaustive surveys in known and/or expected habitat, at appropriate times (diurnal, seasonal, annual), throughout its historic range have failed to record an individual. Surveys should be over a period appropriate to the taxon’s life cycle and life form.
• Critically Endangered (CR)
A taxon is Critically Endangered when the best available evidence indicates that it is not Extinct and it is considered to be facing an extremely high risk of extinction in the wild. Survey should be over a time appropriate to the taxon’s life cycle and life form.
• Endangered (EN)
A taxon is endangered when the best available evidence indicates that it is not Critically Endangered but is considered to be facing a very high risk of extinction in the wild in the near future, as defined by any of the criteria.
• Vulnerable (VU)
A taxon is Vulnerable when the best available evidence indicates that it is not Critically Endangered or Endangered but is therefore considered to be facing a high risk of extinction in the wild in the medium-term future, as defined by any of the criteria.
• Near Threatened (NT)
A taxon is Near Threatened when it has evaluated against the criteria but does not qualify for Critically Endangered, Endangered or Vulnerable now, but is close to qualifying for or is likely to qualify for a threatened category in the near future.
• Least Concern (LC)
A taxon is Least Concern when it has been evaluated against the criteria and does not qualify for Critically Endangered, Endangered, Vulnerable or Near Threatened. Widespread and abundant taxa are included in this category.
• Data Deficient (DD)
A taxon is Data Deficient when there is inadequate information to make a direct, or indirect, assessment of its risk of extinction based on its distribution and/or population status. A taxon in this category may be well studied, and its biology well known, but appropriate data on abundance and/ or distribution are lacking. Data Deficient is therefore not a category of threat. Listing of taxa in this category indicates that more information is required and acknowledges the possibility that future research will show that threatened classification is appropriate. It is im portant to make positive use of whatever data are available. In many cases great care should be exercised in choosing between DD and a threatened status. If the range of a taxon is suspected to be relatively circumscribed, and a considerable period of time has elapsed since the last record of the taxon, threatened status may well be justified.
• Not Evaluated (NE)
A taxon is Not Evaluated when it has not yet been evaluated against the criteria.
The Uses of the Red Lists are:
(1) Developing awareness about the importance of threatened biodiversity;
(2) Identification and documentation of endangered species;
(3) Providing a global index of the decline of biodiversity;
(4) Defining conservation priorities at the local level and guiding conservation action.