Lying In Wait For Extinction

Scientists Robert Reed and Richard Shine say due to a lack of good data on the abundances and population trends of snakes, we may not realize that they are declining until populations have already crashed. It would be useful to have a way of predicting those species most likely to decline before they are in danger. Threatened snakes may share ecological characteristics that predispose them to population declines, especially in the face of human-caused habitat alteration. Reed and Shine examined the ecological correlates of conservation status among 75 species of Australian snakes of the family Elapidae. These elapid snakes are related to cobras, and include some of the most venomous snakes on earth. However, many species are small and relatively innocuous.

Data gleaned from examination of over 18,000 preserved Australian elapid snakes from museums all over the world found that typical predictors of threatened status (like large body size, being a dietary specialist, or low numbers of offspring) did not apply among Australian elapid snakes. Instead, aspects of a snake's mating system were important, as was its method of prey capture. Survival of females is vital to maintaining a population, but Reed and Shine found that females of threatened snake species are apparently highly visible to humans, and tend to be killed in high numbers relative to males. The most striking finding was that snakes that wait for their prey (ambush predators) are more likely to be threatened than are snakes that hunt for their prey (active foragers). An active forager can increase its hunting activity once a habitat is disturbed and the populations of prey animals decline, thus making up for the lower prey density. The ambush forager cannot make up this deficit, so it takes in less energy, ultimately decreasing the production of offspring. Long-term population declines may be the result.

The scientists identified about a half dozen snake species that are not officially considered to be threatened by Australian wildlife agencies, but which are ecologically similar to other threatened species. Most of these are ambush predators, and population declines have already been noticed in some of these species. Preventing these early declines before populations are decimated may greatly reduce the huge cost of saving species with extremely low population sizes.

The study emphasizes that the ghosts of snakes past may predict future conservation problems: the dead specimens collected over two centuries and deposited in museums comprise a vast repository of knowledge waiting to be tapped.