Prey are pressed to make quick decisions once they’ve potentially been detected by an opposing predator. In a trial of life–or–death, prey animals juggle anti–predator decisions when approached. I’ve become fascinated with this topic since starting my graduate work on spot–tailed earless lizards (Holbrookia lacerata), my theory is that these behaviors affect our detection of the species as well as other lacertillians. Lizards have been subjects of ethological study in the past, and have been observed “gambling” in different ways by ethologists and herpetologists (Lizard Ecology, 1994). We can use a few examples from this clade of reptiles to further expand different gambling strategies.
Let’s say you’re a slow lizard, a Texas horned lizard (Phrynosoma cornutum). You feed on harvester ants (Pogonomyrmex spp.), and you’ve made your way to an ant–colony to forage. You wait patiently for ants to come out of their colony. While you’re waiting, a coyote is walking towards your direction. What is the best route to take? Run or stay? Which one should you choose?
It’s a matter of which gamble is optimal. Texas horned lizards are highly cryptic and difficult for surveyors to detect (Sherbrooke, 2003). That being said, the lizard is also very slow. This plays a massive role in the way this lizard’s strategy is made. Depending on the distance of the coyote from your location, the risk of fleeing compared to the risk of staying motionless shifts. The farther away the coyote, the favorable decision (not being eaten) biases towards staying still. You’re a lizard that is hard to see, even more so at a distance, given your similar coloration to the surrounding environment. The closer the coyote gets the favorable decision begins to bias towards fleeing. You’re a slow lizard, so you better run now if the coyote starts to get close to you.
The zebra–tailed lizard (Callisaurus draconoides) adopts a different strategy. These reptiles are lighting fast, can move bipedally, and are well adapted for quick movements (Irschick and Jayne, 1998). Their bodies are sleek, and reserve longer limbs and tails compared to the Texas horned lizard. Though, they aren’t nearly as cryptic given their distinctly black and white patterned tail. As a consequence of the lizard’s conspicuous morphology, the favorable decision biases fleeing earlier during the same predatory approach – it is more likely the coyote has detected the lizard from farther out. The quick zebra–tailed lizard, adapted for this, gladly darts away sooner than the Texas horned lizard (Bulova, 1994; Cooper, 2010).
Ethologists have coined the term “approach distance” or “flight initiation distance”, the distance at which a prey animal chooses to flee from a predator during an approach (Ydenberg and Dill, 1968). The approach distances between the two lizards described here are different, manifested by the “tipping point” between the decisions of fleeing or staying still. When the risk associated with staying still becomes less optimal than fleeing, they do so. Each lizard’s approach distance is the literal point in space at which this shift occurs.
Before learning about anti–predator behavior I never thought that lizards could “think” this way. Who knows if lizards are conscience, or actually think – but the shear fact that they perform this act in the wild boggles my mind. Honestly, it isn’t a surprise I ended up studying and researching this sort of thing for my MSc here at Texas Tech University. I remember trying to catch five–lined skinks (Plestiodon fasciatus) during camping trips. Little did I know that their strategy of escaping a 10 year old boy was much more sophisticated than the boy’s efforts. They had this strategy down to a T, established over eons of evolution.
Bulova, S. J. 1994. Ecological Correlates of Population and Individual Variation in Antipredator Behavior of Two Species of Desert Lizards. Copeia.
Cooper, W. 2010. Initiation of Escape Behavior by the Texas Horned Lizard (Phrynosoma cornutum). Herpetologica.
Irschick, D. J., and B. C. Jayne. 1998. A Field Study of the Effects of Incline on the Escape Locomotion of a Bipedal Lizard, Callisaurus draconoides. Physiological and Biochemical Zoology.
Sherbrooke, W. 2003. Introduction to Horned Lizards of North America. University of California Press. USA.
Vitt, L. J. and E. R. Pianka. 1994. Lizard Ecology: Historical and Experimental Biology. Princeton University Press.
Ydenberg, R. C. and L. M. Dill. 1986. The Economics of Fleeing from Predators. Advances in the Study of Behavior.