According to Assistant Professor Brett Melbourne of CU-Boulder's ecology and evolutionary biology department, who led the research, current mathematical models used to determine extinction threat, or "red-listed" status, of species worldwide overlook random differences between individuals in a given population.
Such differences, which include variations in male-to-female sex ratios as well as size or behavioral variations between individuals that can influence their survival rates and reproductive success, have an unexpectedly large effect on extinction risk calculations, according to the study.
"When we apply our new mathematical model to species extinction rates, it shows that things are worse than we thought," said Melbourne.
"By accounting for random differences between individuals, extinction rates for endangered species can be orders of magnitude higher than conservation biologists have believed," he added.
Currently, extinction risk models are based primarily on two factors, according to Melbourne.
One is the number of random events adversely affecting individuals within a population.
"While a sequence of such random events in a small population can have a big impact, such events are far less likely to affect larger populations," said Melbourne.
The second risk factor used widely in extinction risk models is the impact of external, random events like temperature and rainfall fluctuations that can influence birth and death rates of individuals in a population.
But two additional factors highlighted by the researchers in a new study - sex ratio variations and physical variation between individuals within a population - have been ignored or mischaracterized by most extinction risk modelers.
"There has been a tendency to misdiagnose randomness between individuals in a population by lumping it with random factors in the environment, and this underestimates the extinction threat," said Melbourne.
For the study, the researchers monitored populations of beetles in lab cages and the results were used to test the new mathematical models.
"The results showed the old models misdiagnosed the importance of different types of randomness, much like miscalculating the odds in an unfamiliar game of cards because you didn't know the rules," said Melbourne.
According to the study's authors, "We suggest that extinction risk for many populations of conservation concern need to be urgently re-evaluated with full consideration of all factors contributing to stochasticity, or randomness."