The waiting game: a "battle of waits" between predator and prey

Many prey respond to the presence of a predator by retreatinginto a shell or burrow, or by taking refuge in some other waythat guarantees their safety but restricts further informationfrom being obtained about the predator's continued presence.When this occurs, the individual predator and prey involvedbecome opponents in a "waiting game." The prey must decide howlong to wait for the predator to depart before re-emerging andpotentially exposing itself to attack. The predator must decidehow long to wait for the prey to re-emerge before departingin search of other foraging opportunities. I use a numericalapproach to determine the evolutionarily stable waiting strategyof both players and examine the effects of various parameterson the ESS. The model predicts that each player's waiting distribution—thedistribution of waiting times one would expect to observe forindividuals in that role—will have a characteristic shape:the predator's distribution should resemble a negative exponentialfunction, whereas the waiting time of the prey is predictedto be more variable and follow a positively skewed distribution.The model also predicts that very little overlap will occurbetween the players' waiting distributions, and that the predatorwill rarely outwait the prey. Empirical studies relating tothe model and comparisons between the waiting game and the asymmetricwar of attrition are discussed.     

Visual predators impose correlational selection on prey color pattern and behavior

Several lines of indirect evidence suggest that selection imposedby predators may favor certain combinations of prey colorationand behavior at the expense of other combinations, but thishypothesis has never been tested experimentally. We manipulatedcolor pattern and behavior of pygmy grasshoppers (Tetrix subulata)and exposed them to predation from domestic chickens. We paintedgrasshoppers either uniformly black or striped and manipulatedtheir behavior by changing the ambient temperature. We foundthat the striped pattern enhanced grasshopper survival whenreaction distance was short and jumping performance poor, butit decreased survival when reaction, distance was long and performancehigh, relative to uniformly black individuals. To our knowledge,this is the first experimental demonstration that selectionmediated by visual predators acts on the combination of preycolor pattern and behavior. Further studies are necessary, however,to clarify how widespread correlalional selection is in coevolvedpredator-prey relationships. Correlational selection may resultin genetic coupling between traits, influence the dynamics ofpolymorphisms, and promote the evolution of sexual dichromatismin animals exhibiting sexual differences in behavior. Our resultsalso illustrate the potential importance of visual illusionscreated by moving objects and suggest that it may be dangerousto make inferences about the relative survival value of differentcolor patterns from the outcome of experiments that do not takeinto account prey behavior.     

Corticosterone manipulation reveals differences in hierarchical organization of multidimensional reproductive trade-offs in r-strategist and K-strategist females

Life history trade-offs are often hierarchical with decisions at one level affecting lower level trade-offs. We investigated trade-off structure in female side-blotched lizards (Uta stansburiana), which exhibit two evolved strategies: yellow-throated females are K-strategists and orange-throated are r-strategists. Corticosterone treatment was predicted to differentially organize these females' reproductive decisions. Corticosterone-treated yellow females suppressed reproduction but survived well, and augmented egg mass without decreasing clutch size. Conversely, corticosterone enhanced mortality and reproductive rates in orange females, and increased egg mass only after lengthy exposure. Corticosterone did not affect post-laying condition, suggesting that corticosterone increased egg mass through enhanced energy acquisition (income breeding). Corticosterone enhanced survival of lightweight females, but decreased survival of heavy females, introducing a foraging vs. predation trade-off. We conclude that rather than being a direct, functional relationship, observed trade-offs between offspring size and number represent evolved differences in hierarchical organization of multidimensional trade-offs, particularly in response to stress.