Some endangered species may face an extinction risk that is up to a hundred times greater than previously thought, according to a new study.   Past studies overlooked random differences between individuals in certain species and populations, thus underestimating their extinction risk.  There are more than 16,000 species worldwide threatened with extinction, according to the International Union for Conservation of Nature.  One in four mammals, one in eight birds and one in three amphibians are on the endangered species list.

The Very Rare Amur Leopard

In the new study released Nature, the current models used draw up such lists typically look only at two risk factors.  One is the individual deaths within a small population.  When a species’ numbers dwindle beyond a certain point, even the loss of a handful of individuals can have devastating long-term consequences because of the increased risk of genetic diseases, infertility, and incompatibility between individuals, concentrating the risk of these and other problems.  The second common factor is the environmental conditions that can influence birth and death rates, such as deforestation or fluctuations in temperature or rainfall, both of which are influenced by global warming.

The study argues that factors must be widened in order to give a fuller picture of extinction risk.  Other factors that must be figured into the equation, according to research leader Dr. Melbourne of the University of Colorado, include  male-to-female ratios in a species, and a wider definition of randomness in individual births and deaths. 

The new mathematical tool will be most useful for biologists who want to assess the survival prospects of species.  With these new complex variables, researchers can more precisely determine whether a fragile population can overcome a sudden decline in numbers, such as through habitat loss, or whether it will be wiped out.