W. E. Jr Cooper’s research while affiliated with Indiana University – Purdue University Fort Wayne and other places

Because time spent in refuge may be costly if prey lose opportunities to forage, fight, or mate, prey allow predators to approach closer before beginning to flee when opportunity costs are high. Because the same opportunity costs may apply to refuge use as to escape, prey should make similar trade-offs between risk of emerging and cost of remaining in refuge. In the Iberian rock lizard, Lacerta monticola, we studied the effects of sex, reproductive season, speed of predator approach, and potential loss of mating opportunities on time spent in refuge following simulated predatory attacks. Lizards of both sexes adjusted refuge use to the level of risk by spending more time in refuge when approached rapidly than slowly. Females remained in refuge for equal times in the mating and postreproductive seasons, but males emerged sooner during the mating season, suggesting adjustment to a cost of lost opportunity to search for mates during the mating season. When a tethered female was nearby, males emerged from refuge earlier than if no female was present, indicating a trade-off between risk and mating opportunity. Approach speed affected emergence time when females were absent, but not when a female was present. Approach speed did not affect the probability that, after emerging, a male would return to court the female. For males that courted females intensely (bit them) before entering refuge, approach speed did not affect latency to emerge, but males that courted less intensely emerged sooner if approached slowly than rapidly. These findings show that males adjust the length of time spent in refuge to both risk of predation and reproductive cost of refuge use.

Optimal emergence theory predicts decisions by prey about when to emerge from refuge based on the assumption that optimal time to emerge is determined by the balance between predation risk and costs of the response to it. Tests have verified the predictions for a variety of risk and cost factors, but have focused on single factors, whereas prey must be able to assess the overall risk and cost based on several factors acting simultaneously. In a factorial experiment in which two of us simulated predators, we tested effects of three simultaneous factors, predator approach speed, directness of approach, and individual differences between predators, on time spent in refuge after escaping by the Iberian rock lizard, Lacerta monticola. Effects of approach speed and directness were significant, the lizards delaying emergence more when the predator approached rapidly and directly. There was a significant interaction between directness and individual predator. Emergence times were similar for the two predators under low risk (indirect approach), but differed under high risk (direct approach). Experiments should use single predators or designs that control for differences among individual predators. All three risk factors affected emergence from refuge. Prey may be challenged by multiple risks and costs at a given time, and must be able to gauge at least the major ones with some degree of accuracy to make appropriate antipredatory decisions. Directness of approach, but neither approach speed nor individual predator, increased the likelihood that a lizard would emerge from refuge at a site other than the point where it entered the refuge. This suggests that lizards assessed directly approaching predators as more likely to have observed the entry point into refuge, and therefore as posing a greater threat upon emergence at the entry point.

A laboratory experiment with the broad-headed skink (Eumeces laticeps) involving staged agonistic encounters demonstrates that larger males have an advantage over smaller ones in agonistic bouts. Field data on head wounds produced by intraspecific fighting during the breeding season show a much higher frequency of new wounds among males over 100 mm in snout-vent-length than in smaller males. The significant difference in new-wound frequency strongly suggests avoidance of fights by the small males, which is corroborated by laboratory and field observations. Access by males to reproductively active females depends on the ability to defeat other males in aggressive contests virtually always involving head biting if the males are of nearly equal size. Because the probability of winning agonistic encounters increases with size, young males avoid fights with older males. Aggressive contests with larger males and reproductive attempts other than courtship in the absence of larger males are deferred. Aggressive behavior in E. laticeps may be employed in direct defense of females, but might also be expressed in defense of specific sites and/or territories. In the laboratory, males in their home cages were significantly more likely to win encounters with males of similar size than were males fighting in the home cages of opponents. This suggests that encounter site could be important in determining encounter outcome and that field study of possible site defense or territoriality is needed.