Saturday, July 25, 2009

The Diamondback Rattlesnake’s Predatory Might

A new project at work has kept me in the field for the last couple of weeks and has severely dimensioned my time available for blogging; I should be freed up by the middle of next week and be able to get Ecographica back in gear then…

On the positive side of things, the abundance of recent fieldwork has resulted in several encounters with nature, and a slow starting Saturday has provided the opportunity to share one such wildlife sighting. However, before proceeding a warning must be forwarded; if you are lucky enough to stumble onto one of these herps in the wild, ensure that you’re stumbling is undertaken with the utmost caution – or your luck may run out very quickly! Although the below video and picture appear to be taken at close range, they in fact have been recorded at a distance and later edited from the safety of a desk.

Getting on with the tale (or, in this instance “tail”), while trudging through a chunk of palmetto flatwoods in north central Florida last week, a break in the radiating palmetto leaves underfoot caught my eye – a diamondback rattlesnake! And a big one at that!

Photo was taken by Charlie, a fellow ecologist that happens to be a little faster at drawing his camera.

The eastern diamondback rattlesnake Crotalus adamanteus is the largest pitviper in the Western Hemisphere and can achieve sizes (length) of more than seven feet. Fairly common here in Florida, their range extends north along the Atlantic seaboard to the Carolinas and westward to about New Orleans, Louisiana. They do well in habitats such as palmetto flatwoods due to the ample cover provided by the palmetto leaves (“palmetto” = Seronoa repens).

The leaves provide shade for regulating body temperatures, conceal them from fumbling ecologists, and offer excellent camouflage for setting ambushes – and setting ambushes is what they do best. They lay in wait for hours, motionless; then, when the radiating heat of an approaching rabbit, bird or other delicacy enters into range, OR when a savory molecule lands on the flicking tongue (vomeronasal organ or “Jacobson’s organ”), STRIKE!

Strike indeed! Strike with the largest fangs of any rattlesnake species and with a venom pact-full of proteins adapted to produce hemorrhaging and tissue necrosis.

Here's a quick video of the same specimen. He's on the move, so I paused the video a couple of seconds at the start; his head is near the upper right-hand corner - look for the curser.

Although the food capturing mode of Crotalus adamanteus can easily be described as “predatory,” their relative contribution, or “predatory influence,” within ecosystems is not especially clear. Typically, when viewing a system’s predator-prey functionality the response and feedback between prey availability (how many are present) is weighed against the number of predators acting antagonistically within the system.

For example, one question that could be posed in regards to the predator function of Crotalus is “how does a surge in rabbit numbers (prey) affect the longevity and reproductive success (population) of the eastern diamondback?” This may seem pretty much straight forward, however; the ability of reptiles to control or impact prey populations within a given environment may be somewhat different than those of endothermic predators; after all, the biology and physiology of ectotherms is considerably different – they posses a different metabolic scheme altogether.

In examination of predator function within the Viperidae (the Family to which the eastern diamondback is a member), Erika Nowak of the US Geological Survey and others concluded that in comparison to predator-prey models established for mammals, the ectothermic vipers contribute a lesser prey population regulating potential.

The reasons for the Viperidae’s decrease in predator functionality include:
1. Longer prey handling times due to a comparatively limited digestive capability
2. Increased tolerances for fasting
3. An increased ability to convert food into fitness currency (progeny)
4. A limited ability for rapid reproductive tracking of short-term prey abundance.

Their article (Functional and Numerical Responses of Predators: Where Do Vipers Fit in the Traditional Paradigms?) Strongly points to the need for additional research in several areas behavioral ecology. I fully agree with this assessment, but for whosoever takes on the task - watch your step!

Erika M. Nowak1, Tad C. Theimer, Gordon W. Schuett (2008). Functional and Numerical Responses of
Predators: Where Do Vipers Fit in the
Traditional Paradigms? Biological Reviews, 83 (4), 601-620

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