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Hopes up for species survival

By Gracie Valena - 23 May 2011 2:54:1 GMT
Hopes up for species survival

Two recent researches find that species extinction, while still very real, may not be as bad as it's been thought, calculated, and reported to be.

A report in the May 19th issue of Nature says that calculations used for determining extinction rates have been flawed, resulting in overestimation that can be greater than 160 percent, while a report in Trends in Ecology and Evolution gives the good news that species that were considered too rare to save, such as the Siberian Tiger, could be saved as long as conservation efforts can target key threats.

Wrong species-area relationship

This indirect method for estimating extinction rates considers the number of species found in a given area and then estimates how the number of species grows as the area expands. Then the calculation is reversed to estimate the loss of species due to habitat loss.

Stephen Hubbell, a distinguished professor of ecology and evolutionary biology at UCLA and co-author of the Nature paper explained about how large the margin of error of the method is ''The overestimates can be very substantial. The way people have defined 'extinction debt' (species that face certain extinction) by running the species-area curve backwards is incorrect.'' He adds however, ''but we are not saying an extinction debt does not exist.''

He asserts, ''I don't want this research to be misconstrued as saying we don't have anything to worry about when nothing is further from the truth.''

Hubbell says of the predictions in the 1980s that half of the species on Earth would be lost by 2000, ''Nothing like that has happened … However, the next mass extinction may be upon us or just around the corner. There have been five mass extinctions in the history of the Earth, and we could be entering the sixth mass extinction.''

Hubbell and co-author Fangliang He used data from the Center for Tropical Forest Science covering areas in Asia, Africa, South America and Central America involving 4.5 million trees and 8,500 tree species.

Mistaken MVP

Meanwhile, Philip Stephens of the School of Biological and Biomedical Sciences, Durham University and Greg Hayward of the U.S. Forest Service reported that the use of the minimum viable population (MVP - the size of a population that is thought to have a specified probability of persistence for a given period) numbers in conservation is wrong. They say that there is no single population size that can be used as a catch-all guideline to save endangered species and even species such as the mountain gorilla (about less than 1,000), tha Amur or Siberian tigers (about 450), the Philippine eagles (less than 500) and the Puerto Rican parrots (only 70 left) can still survive.

Stephens explained ''Populations usually show rapid declines as a result of human activities such as hunting and habitat conversion. The results of the study are encouraging and show that if we can remove the negative effects of human activities, even relatively small populations could be viable in the long term.''

The study finds that population sizes required for long-term viability changes, and depend on specific circumstances of each population. Its real impact is on policies. In the past, studies that called for larger numbers for a species to be viable tended to influence the allocation of funds away from what were considered hopeless cases.

The researchers are now saying that conservationists should not give up on saving an endangered species if its population is below an MVP figure, and they advise policy-makers to be cautious about setting guidelines for 'safe' population sizes.

However, the opposite scenario also works. Curt Flather, a research ecologist with the USFS Rocky Mountain Research Station in Colorado noted ''The enormous variability in estimates shows that many populations also need to be highly abundant to be viable. The extinction of the passenger pigeon, which numbered 3 to 5 billion individuals in North America during the 1800s, is a reminder that population size alone is no guarantee against extinction.''

Thus, there is really a need to think outside the box when it comes to conservation. Steve Beissinger, a Professor at the University of California, Berkeley, said ''Viability depends on the idiosyncrasies of the factors causing a species to decline, and there is no single population size that guarantees safety for all species. There's more that matters than just size.''

Top Image Credit: Philippine Eagle © Timclaire