TRADEOFFS BETWEEN PREDATION RISK AND FEEDING IN A LIZARD, THE BROAD-HEADED SKINK (EUMECES LATICEPS)

Foraging, feeding, and escape decisions may all be modified by threat of predation. Field experiments using a human simulated predator show that a lizard, the broad - headed skink, Eumeces laticeps, alters several aspects of feeding behavior in ways suggesting tradeoffs between predation risk and feeding. When food (cricket) was closer to the predator, the lizards more frequently did not attack it, and often retreated to safety before consuming it, reducing the duration of exposure to predation. The probability of attacking a cricket decreased with distance of the lizard from refuge, reflecting greater risk due to increased time required to reach refuge. Latency to attack increased with distance of the lizard from refuge, suggesting that lizards assessed the risk as acceptable after observing the predator's continued immobility. Large crickets were attacked with higher probability and shorter latency than small crickets, indicating that greater risk was acceptable for greater energetic benefit. The lizards more frequently carried large than small crickets to refuges before eating them, reducing duration of exposure because handling time was greater for larger crickets. Smaller crickets were consumed where captured, again indicating modification of feeding behavior in response to predation risk. The skinks also reduced risk by reducing handling time when closer to the predator. Escape was delayed until a predator approached closer when lizards were eating than when not eating. This delay may reflect a tradeoff between predation risk and acquisition of food.

Reactive and anticipatory display to deflect predatory attack to an autotomous lizard tail

Antipredation display is usually directed to predators that have been detected, but might be beneficial when predators are likely to be dangerously close, but undetected. Anticipatory display could be selectively favored if it increased the probability of escape sufficiently to outweigh the increased probability of being detected and captured by a previously unaware predator. This is especially likely if prey have adaptations permitting a high probability of escape when attacked, such as deflection of attack to dispensible parts. Deflective displays typically occur under threat of imminent attack by a predator detected within striking distance, but might also occur in circumstances reliably entailing a high risk of ambush by undetected predators, especially immediately after an animal stops following a bout of locomotion. Tail undulation was observed in the broad-headed skink (Eumeces laticeps), a lizard with a conspicuous, autotomous tail that enhances escape ability. Eumeces laticeps undulated its tail before fleeing from a looming predator and immediately after stopping in the absence of a detected predator. Undulation after stopping confirms predictions of anticipatory deflective display and contradicts alternative hypotheses. Undulation just before flight from a predator very close at hand is a form of reactive deflection.

Risk Factors and Emergence from Refuge in the Lizard Eumeces Laticeps

I studied effects of three risk factors, predator proximity, persistence in attacking, and speed, on latency to emerge after entering a refuge in the scincid lizard Eumeces laticeps. I simulated a predator by directly approaching a lizard until it took refuge, usually a tree hole. Costs per unit time of lost opportunities to forage or engage in other activities enhancing fitness did not vary with risk factors. Skinks remained in refuges longer when I stayed near the refuges than when I withdrew to a greater distance. At both distances, skinks monitored my presence visually from positions at or near refuge entrances. Skinks remained in refuges longer after the second of two successive similar approaches at the same speed than after the first, suggesting that they perceived increased risk due to persistence by an individual predator, but the assessment might have been based on attack rate without individual recognition. Latency to emergence increased with predator approach speed, giving another indication of response to higher risk. If lizards were approached twice in succession, latency to emergence was much greater when predator speed was faster during the second approach. When the second approach was slower, there was no significant difference in latency between trials. Risks associated with speed and persistence thus simultaneously affect risk assessment. A recent model (Sih, 1992) of emergence from refuge supposes that decisions affecting latency to emerge are based on a balance of costs of remaining in refuge (often predominantly costs of lost opportunities for feeding or mating) against risk of predation. All data are consistent with a generalized view of Sih's (1992) model, but studies are needed to assess effects of cost and limited information about predator presence.