TheIUCN Red List provides the public with information regarding the conservation status of animal, fungi, and plant species.[3] It divides various species into seven different categories of conservation that are based on habitat range, population size, habitat, threats, etc. Each category represents a different level of global extinction risk. Species that are considered to be critically endangered are placed within the "Threatened" category.[4]
As the IUCN Red List does not consider a species extinct until extensive targeted surveys have been conducted, species that are possibly extinct are still listed as critically endangered. IUCN maintains a list[5] of "possibly extinct" and "possibly extinct in the wild" species, modelled on categories used byBirdLife International to categorize thesetaxa.
To be defined as critically endangered in the Red List, a species must meetany of the following criteria (A–E):[6]
A) Reduction in population size based on any of the following:
1. An observed, estimated, inferred or suspected population size reduction of≥ 90% over the last 10 years or three generations, whichever is the longer, where thecauses of the reduction are reversible AND understood AND ceased, based on (and specifying) any of the following:
a. direct observation
b. an index of abundance appropriate for the taxon
c. a decline in area of occupancy, extent of occurrence or quality of habitat
2. An observed, estimated, inferred or suspected population size reduction of≥ 80% occurred over the last 10 years or three generations, whichever is the longer, where the reduction or itscauses may not have ceased OR may not be understood OR may not be reversible, based on (and specifying) any of (a) to (e) under A1.
B) Geographic range in the form of either B1 (extent of occurrence) OR B2 (area of occupancy) OR both:
1. Extent of occurrence estimated to beless than 100 km2, and estimates indicating at least two of a-c:
a.Severely fragmented or known to exist at only one location.
b.Continuing decline, inferred, observed or projected, in any of the following:
i. extent of occurrence
ii. area of occupancy
iii. area, extent or quality of habitat
iv. number of locations or subpopulations
v. number of mature individuals
c.Extreme fluctuations in any of the following:
i. extent of occurrence
ii. area of occupancy
iii. number of locations or subpopulations
iv. number of mature individuals
2. Area of occupancy estimated to beless than 10 km2, and estimates indicating at least two of a-c:
a.Severely fragmented or known to exist at only one location.
b.Continuing decline, inferred, observed or projected, in any of the following:
i. extent of occurrence
ii. area of occupancy
iii. area, extent or quality of habitat
iv. number of locations or subpopulations
v. number of mature individuals
c.Extreme fluctuations in any of the following:
i. extent of occurrence
ii. area of occupancy
iii. number of locations or subpopulations
iv. number of mature individuals
C) Population estimated to number fewer than 250 mature individuals and either:
1. An estimated continuingdecline of at least 25% within ten years or three generations, whichever is longer, OR
2. A continuing decline, observed, projected, or inferred, in numbers of mature individuals AND at least one of the following (a-b):
a. Population structure in the form of one of the following:
i. no subpopulation estimated to contain more than 50 mature individuals, OR
ii. at least 90% of mature individuals in one subpopulation
b. Extreme fluctuations in the number of older individuals
D) Population size estimated to number fewer than 50 mature individuals.
E) Quantitative analysis showing the probability of extinction in the wild is at least 50% within 10 years or three generations, whichever is the longer.
The Beluga sturgeon (Huso huso) is an example of a critically endangered species. Their wild populations have been reduced significantly due to overharvesting for itscaviar.
The current extinction crisis is witnessing extinction rates that are occurring at a faster rate than that of the natural extinction rate. It has largely been credited towards human impacts onclimate change and theloss of biodiversity. This is along with natural forces that may create stress on the species or cause an animal population to become extinct.[7]
Currently, the biggest reason for species extinction is human interaction resulting in habitat loss.[8] Species rely on their habitat for the resources needed for their survival. If the habitat gets destroyed, the population will see a decline in their numbers. Activities that cause loss of habitat include:pollution,urbanization, andagriculture. Another reason that plants and animals become endangered is due to the introduction ofinvasive species. Invasive species invade and exploit a new habitat for its natural resources as a method to outcompete the native organisms, eventually taking over the habitat. This can lead to either the native species' extinction or causing them to become endangered, which also eventually causes extinction. Plants and animals may also go extinct due to disease. The introduction of a disease into a new habitat can cause it to spread amongst the native species. Due to their lack of familiarity with the disease or little resistance, the native species can die off.
.jpg)
