Apr. 2, 2002 Some species die out after their habitat is disturbed while others continue to thrive -- the big question is why? New research shows that part of the answer for threatened Australian snakes is that they ambush their prey instead of hunting actively. This work may help conservationists identify at-risk snakes before it's too late.
Currently, "declines may be difficult to assess until they have progressed to the point where remedial actions are difficult or impossible," say Bob Reed, who did this work while at the University of Sydney in Australia and is now at the Savannah River Ecology Laboratory in Aiken, South Carolina, and Rick Shine of the University of Sydney in Australia in the April issue of Conservation Biology.
Australia has a rich diversity of terrestrial reptiles -- about 700 species compared to fewer than 250 species in the U.S., which is about the same size. Most Australian reptiles are so little known that biologists can't even assess their conservation status.
To help find a simple way of identifying at-risk reptiles, Reed and Shine studied ecological and behavioral traits that correlate with vulnerability in about Australia's terrestrial elapid snakes, which are venomous and comprise about 75 species. The researchers assessed 19 traits based both on existing field observations and on data from measuring and dissecting more than 18,000 preserved specimens. The traits ranged from foraging behavior (ambush vs. active hunting) to reproduction type (egg-laying vs. livebearing) to use of 25 habitat types (such as grassland, forest and swamp).
Reed and Shine found two main behavioral differences between threatened and non-threatened elapid snakes in Australia: most of the threatened snakes both lack male-male combat and rely on ambush foraging. About 80% of the threatened snakes lack male-male combat. These species tend to have larger females, which would put them at risk if people killed a disproportionate number of reproductive females. This hypothesis is supported by the fact that museum collections of the threatened snake species have about 15% more females than males.
Half of the 8 ambush predator species are classified as threatened while fewer than a tenth of the active hunter species are threatened. Snakes that ambush their prey need to be able to hide in thick leaf litter and other particular ground covers. Land conversion often destroys these ground covers, which eliminates the snakes' ambush sites and often decreases the abundance of prey. Because these snakes sit and wait for their prey instead of searching for it, this means they don't get enough to eat -- and their reproductive rate and then their population declines. In contrast, snakes that actively hunt can more easily adapt to different types of ground cover as long as their prey remains abundant.
Reed and Shine's ecology-based analysis predicted the snakes' conservation status quite accurately, correctly identifying 90% of the species listed as threatened. The researchers also identified six species that are not listed as threatened but have the ecological traits associated with being endangered, and they recommend that managers study these six species more closely. Ecology-based analysis could help conservationists manage species "on a proactive rather than a reactive basis," say Reed and Shine.
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