Speed Kills. Or Does It?
In an eat or be eaten world, the survival of the fittest can come down to who the most physically able is. Today’s paper investigated the athletic ability of sidewinder rattlesnakes relative to their kangaroo rat prey. (Image Credit: Tigerhawkvok, CC BY-SA 3.0).
Determinants of predation success: How to survive an attack from a rattlesnake (2019) Whitford et al., Functional Ecology, https://dx.doi.org/10.1111/1365-2435.13318
In nature, many animals are part of the predator-prey cycle. One animal is subject to being eaten by the other, and must escape in order to avoid this fate. Despite what you may have seen on a variety of amazing nature documentaries, most predator-prey interactions don’t involve some flashy takedown and subsequent meal for the predator. Predators usually fail far more often than they succeed, with one of the most successful animals on the planet (the killer whale) only succeeding HALF of the time.
These interactions between predators and their prey depend on two things: the predator’s physical attack ability/performance and the prey’s escape ability. Basically, who is more athletic? There are many different ways that predators try and take down their prey, but the authors of today’s paper wanted to know what the key aspects of the predator-prey interaction are, and which of them is most important for each participant.
What They Did
An ideal system for studying the predator-prey interaction is that of the sidewinder rattlesnake (Crotalus cerastes) and desert kangaroo rat (Dipodomys deserti). Sidewinders are sit-and-wait predators, waiting outside of the burrows of their prey to ambush and (ideally) consume them. To monitor these predation events, the authors tracked sidewinders to the burrows of kangaroo rats and, once they determined which burrow the snake was going to use, they set up high-speed cameras to record the ambushes. In the event of successful ambushes, they also tracked the attacked rat and recorded its fate.
Using the recordings of the ambushes, the authors analyzed the time it took the rat to react/try to evade, how long the snake’s attack took, the length of the snake’s strike, the duration of the snake’s bite (the longer the better for a snake that injects venom), and the accuracy of the snake’s strike. All of these variables were used together to determine what was most important for a successful snake strike: the strike of the snake or the evasiveness of the rat?
Did You Know: Predation Types
The snakes used in this study are known as sit-and-wait predators because they (wait for it) sit and wait to ambush their prey. There are a variety of other animals that do the same thing, but two other major predator types are the sit-and-pursue and the active-pursuit predator.
Sit-and-pursue predators, like the cheetah, wait for when a prey animal gets close enough to them, at which point they will spring into action and chase down their prey. Active-pursuit animals, like the wolf, will simply look for and chase down any prey animal they can find, usually resulting in long chases where they exhaust their prey so much that they become an easier meal.
What They Found
Not surprisingly, the evasiveness of the rat influenced the likelihood of a successful strike. The distance and speed of the snake’s strike had no effect on how successful the strike was. This is in direct contrast to the classic idea that speed is the most important factor in predator-prey interactions.
In addition to their reaction speed, bitten kangaroo rats relied on body contortions and kicks to try and forcibly dislodge the fangs of the snakes from their bodies, reducing the time that the snake had to inject potentially lethal venom. These kicks and body twists meant that most of the rats that used them were able to survive their bite wounds.
In total, the authors used 23 strikes from 12 different snakes in their analyses. This may seem like a low number (and for some systems it is), but it is a testament to the hard work and dedication of these scientists that they were able to track and record even that many snakes. The only potential problem could be that these low numbers resulted in the unexpected finding that speed is not the most important aspect of successful predation events. Further studies may shed more light on this system and the subtle intricacies therein.
This study has highlighted aspects of the predator-prey relationship, accuracy and reaction times, that were previously thought to be not as important as speed. The authors note that these nuanced results may be specific to this system, but stress that more studies in the future should consider the various aspects of the specific predator-prey relationships studied, instead of simply noting how fast a given predator or prey species was.