rarity

views updated May 17 2018

rarity The relative abundance of a species and, therefore, its vulnerability to extinction. The International Union for Conservation of Nature and Natural Resources measures the vulnerability of a species according to five criteria: (a)the rate at which its numbers are observed, inferred, or projected to be declining;(b)in association with (a), whether the species occurs as a single, small population or a few, small, fragmented ones;(c)in association with (a), whether the species occupies a small geographic range or area;(d)the size of the population;(e)a mathematical estimate of the predicted risk of extinction within a specified time. From this assessment, species are allocated a position on a continuum of increasing threat with three categories: as ‘critical’; ‘endangered’; or ‘vulnerable’. Species that are known to be at risk of extinction, but fail to qualify for any of the main categories, are classified as ‘susceptible’.

rarity

views updated Jun 08 2018

rarity The relative abundance of a species and, therefore, its vulnerability to extinction. The International Union for Conservation of Nature and Natural Resources measures the vulnerability of a species according to five criteria: (a) the rate at which its numbers are observed, inferred, or projected to be declining; (b) in association with (a), whether the species occurs as a single, small population or a few, small, fragmented ones; (c) in association with (a), whether the species occupies a small geographic range or area; (d) the size of the population; (e) a mathematical estimate of the predicted risk of extinction within a specified time. From this assessment, species are allocated a position on a continuum of increasing threat with three categories: as ‘critical’, ‘endangered’, or ‘vulnerable’. Species that are known to be at risk of extinction, but fail to qualify for any of the main categories, are classified as ‘susceptible’.

rarity

views updated May 17 2018

rar·i·ty / ˈre(ə)ritē/ • n. (pl. -ties) the state or quality of being rare: the rarity of the condition. ∎  a thing that is rare, esp. one having particular value as a result of this: to take the morning off was a rarity.