Did you ever check out what measures are used to define how much species are threatened? Since I have been using the terms repeatedly in my photo essays, I thought it wouldn’t hurt to summarize them.
Café Discovery has been, after all, mostly about words and phrases and meaning. Or at least, it has tried to be.
The International Union for Conservation of Nature maintains a Red List. of threatened species. The categorization they used ranks species as, from worst on down, extinct, extinct in the wild, critically endangered, endangered, vulnerable, conservation dependent, near threatened, or least concern. Of course, there are also situations in which there is not enough data and also cases where species have just not been evaluated.
Conservation dependent (CD) is a category no longer used except for species who were previously in that category and have yet to be re-evaluated. A taxon was considered CD if it was “dependent on conservation efforts to prevent the taxon becoming threatened with extinction.” (Wikipedia entry) So one will still encounter the label, as with giraffes, for instance.
The first two categories are quite clear:
EXTINCT (EX): A taxon is Extinct when there is no reasonable doubt that the last individual has died.
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.
So is the last one. A taxon is LEAST CONCERN (LC) when it has been evaluated against the criteria and does not qualify for anything else.
The others are trickier.
CRITICALLY ENDANGERED (CR): A taxon is Critically Endangered when the best available evidence indicates that it meets any of the criteria A to E for Critically Endangered (see Section V), and it is therefore considered to be facing an extremely high risk of extinction in the wild.
The devil is often in the details. Section V is chock full of details. If someone finds my summary misses the point, I will stand corrected. 🙂 If we get this one, the others are easy, since it is mostly a change of numbers in an algorithm.
Criterion A is about population reduction. It makes sense to consider population afer all. If a species has had its population reduced by 90% (80% if we don’t know why it is happening) over the last ten yeats or three generations, whichever is less, it is critically endangered. If it is even suspected that this is happening, it is considered to be the same as having proof that it is happening as long as there is data to back up the suspicion. That is, it takes evidence of some sort and the rules for what constitutes evidence are laid out in Section V.
Criterion A differs for ENDANGERED (EN), where the rate of reduction is 70% (50% if we don’t know why), and VULNERABLE (VN), where the rate is 50% (30%).
Criterion B concerns habitat. If its range is less than 100 square kilometers, fragmented and declining, or is less than 10 square kilometers and is the only location or the number of locations is in rapid decline or those locations are becoming seriously fragmented, a species is considered CR. For EN, the numbers are 5000 and 50. For VU, they are 20,000 and 2,000.
Criterion C is population size. Any species with less than 250 mature members is considered CR provided either there is an estimated continued decline of 25% or greater over the next three years or one generation, whichever is greater (up to 100 years) or something more complicated: if the population is in decline and no subpopulation exceeds 50 individuals or at least 90% of all adults are in one population or there is extreme fluctuation in the population structure in general (i.e. the entire population has a reasonable chance of dying off as a matter of “bad luck”). For EN, the numbers change to 2500 mature individuals, decline of 20% over the next five years or two generations (whichever is greater, up to 100), or no subpopulation over 250 or 95% in one subpopulation. For VU: 10,000 mature individuals, continued decline of over 10% over 10 years or three generations or all mature individuals in one subpopulation.
Criterion D: Population size is less than 50 mature individuals for CR (250 for EN). For VU: 1,000 mature individuals or
Population with a very restricted area of occupancy (typically less than 20 [square kilometers]) or number of locations (typically five or fewer) such that it is prone to the effects of human activities or stochastic events within a very short time period in an uncertain future, and is thus capable of becoming Critically Endangered or even Extinct in a very short time period.
Criterion E: If quantitative analysis show that the probability of moving into the category EW is at least 50% within the next 10 years or three generations (up to 100 years), the species is CR. If we substitute 20%, five years and two generation, the species is EN. If a species has a probability of becoming EW of 10% over the next 100 years, it is considered VU.
Now we can escape Section V and return to the last of the categories.
A taxon is NEAR THREATENED (NT) when it has been 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.
Confused yet? Looking for loopholes?