Getting to Know About the Extinction Threshold of Animal Populations

Getting an idea about the extinction threshold of endangered animals is very important for the wildlife manager. It is not an easy task. A new study by Dr John Drake, an ecologist at the University of Georgia, Athens, and Dr Blaine Griffen of the University of South Carolina, Columbia, provides a statistical alarm beeper for the manager.

The major causes of animal extinctions today are habitat loss and degradation, invasive species, poaching and pollution. But to say when an endangered population will become so endangered that it is doomed to extinction if nothing is done to help is an almost an impossible task.

The results of the new study are based on a simple laboratory experiment, but if the technique works in the wild, it could help wildlife managers know when they need to put in that extra effort.

Theoretical biologists have surmised that the tipping point toward extinction would be preceded by a phase of critical slowing down. This means that a population takes longer and longer to bounce back from small declines.

In the experiment the scientists set up 60 small tanks and put populations of water fleas (Daphnia magna) in each. After letting the Daphnia get settled for several months, Dr Griffen mimicked environmental degradation in half the tanks by gradually cutting back the blue-green algae he fed them. These nutrition deprived populations began to slowly shrink. After about 270 days, they passed a tipping point and died out within a year. The other 30 populations, which received a stable food supply, fluctuated in size but persisted.

Dr Drake then analyzed the trends in population size. Four statistical measures of abundance showed signs of critical slowing down in the degraded environments but not in the healthy ones. The slowing down lasted as long as eight generations before the populations crossed the tipping point to extinction.

The study has exciting prospects for the wildlife manager. Come on guys ,pay more attention to your environment and fine tune your filed observations.

The study by Dr Drake and Dr Griffen appear in the latest issue of Nature.