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Alcock Chapter 6 - “Behavioral Adaptations for Survival”. Really about predator/prey relationships. In the larger context, this is one aspect of Behavioral Ecology 1 There are different interactions between organisms -predator-prey parasite-host symbiosis mutualism The interactions relative to predatory-prey and parasite-host involve communication. It is often interesting to analyze whether the communication is honest or deceitful. 2 Cryptosis & mimicry. These anti-predator strategies may involve one or more forms of biological deceit -- that is, you attempt to portray yourself as something different from reality. cryptosis • hiding • mimicry • camouflage 3 Biston betularia (camo moth) Question: What does the previous example (Figure 6.16 in the text) have to do with behavior? 5 Skipper butterfly caterpillars that eject feces from their hiding spots.... 6 6.21 Personal hygiene by a skipper butterfly larva may be an antipredator adaptation Trachops finds dinner Deception is also prevalent with parasitehost interactions. Consider the famous case of Oropendolas and Cow birds... 22 Oropendola … and nest Cowbird Bot flies and a squirrel with an infestation. A deceptive mimic -- The fly mimics the very predator that is after it. fly jumping spider On the other hand, there can be honest signals used as anti-predator devices: Stotting in Springboks/ Gazelles Hypotheses for why stotting occurs: 1. Alarm signal: Warn neighbors who are related to you. 2. Social cohesion signal: Do it to bring group together. 3. Confusion effect: Predator will be confused by odd behavior and go after someone else in the group. 4. Honest signal of unprofitability: Anyone who can jump that high can outrun me, says the predator, I better pick a different target. 29 Predictions from each hypotheses You honestly communicate to the predator that you are the most costly prey item. Of course this strategy only works if you are in a group, and the predator has the sophistication to get the point! So the behavior works… For stotting to work, first there had to be herding. Why is there herding behavior? Or schooling behavior? Many individuals moving in a coordinated way become a large visual mass. That is, the predator doesn’t see many fish, the predator sees a large undulating “whale”. Hypothetically, a gene shows up that causes one individual to prefer hanging close to a con-specific. A predator eats your neighbor, and you leave more genes in the next generation. So the “grouping” gene becomes fixed. Everyone trying to hide behind everyone else makes an instant herd As a corollary, the most aggressive and strongest individuals should successfully compete for the best position in the herd (the center). Individuals in large groups have lower predation risk Anolis doing a push-up Smaller fish are more likely to be attacked From electric fish behavior study we learn that there is a preferred prey size. In one sense, this is obvious. You have to be physically adapted to capture, eat prey of a certain size, or toughness, etc. This begs the question, though, of whether predators forage optimally, or just settle for anything that is acceptable. The term “optimal” is not the best. It implies some animals or groups make bad choices if they are not optimizing their food selection. 47 Eat anything that vaguely resembles food. Continuous Range Very selective about what to grab, eat. Each strategy across range can be equally “optimal”. Being “efficient” as a predator is not always the best way to leave more genes in the next generation. Crows prefer large whelks The large ones only have to be dropped from 5 meters. Almost no drops of large whelks from > 5 m. A higher proportion of the smaller whelks are dropped from a higher point (more energy to fly higher). When there are multiple selection pressures, there is no one best strategy for foraging. Recall Tungara frog: There was no one best strategy for mate advertisement. Similarly, for foraging, skinks trade off the distance they will travel from shelter for good food vs the need to avoid snake predation… Also, what is optimal at one time of day (or season, etc) is not necessarily optimal at other times… 54 • The most efficient foraging by ants in colony with head sizes 2.2-2.6 mm. • These larger ants are more likely to be preyed upon by parasitic flies. • The flies are only active during the day. • So colony sends out smaller foragers during day, and “optimal” foragers at night. The classical prisoner's dilemma (PD; see text pg 469, 9th edition text):" Two accomplices, Fluffy and Prunella, are going to rob a bank. Beforehand, they agree that if they are caught each should remain silent and not rat out the other. Neither really trusts the other, however." Well Fluffy and Prunella are caught, and held in separate cells. The police have insufficient evidence for a conviction, but they offer each the same deal: " If one testifies for the prosecution against the other (rats), and the other remains silent, the betrayer goes free = the temptation. The silent accomplice receives the “sucker” payoff, a full 10-year sentence. " If both stay silent, both prisoners are sentenced to only six months in jail for a minor charge. " If each betrays or rats out the other, each receives a five-year (reduced) sentence for cooperating. " Each prisoner must make the choice of whether to betray the other or to remain silent. The dilemma is that neither prisoner knows for sure what the other prisoner will do. " Prunella Stays Silent Fluffy Stays Silent Prunella betrays or defects and rats out Fluffy Fluffy = Minor sentence, serves six months Fluffy = Sucker payoff, serves ten years Prunella = Minor sentence, serves six months Fluffy Betrays Fluffy = Temptation payoff, goes free or defects and rats Prunella = Sucker payoff, serves ten years out Prunella Prunella = Temptation payoff, goes free Fluffy = Reduced sentence of five years Prunella = Reduced sentence of five years Given these payoff values: Temptation > Minor > Reduced > Sucker What do you do? If you know your accomplice will remain silent, it is in your best interest to remain silent too. Since you are unsure, however, the best strategy is to defect, avoid the sucker payoff and accept the reduced sentence. Prunella Stays Silent Fluffy Stays Silent Prunella betrays or defects and rats out Fluffy Fluffy = Minor sentence, serves six months Fluffy = Sucker payoff, serves ten years Prunella = Minor sentence, serves six months Fluffy Betrays Fluffy = Temptation payoff, goes free or defects and rats Prunella = Sucker payoff, serves ten years out Prunella For Prunella = 50% chance of getting 6 months and 50% chance of worst sentence! Prunella = Temptation payoff, goes free Fluffy = Reduced sentence of five years Prunella = Reduced sentence of five years For Prunella = 50% chance of getting best deal (go free) and 50% chance of reduced sentence. No chance of worst sentence! Terns can either hunt for fish, or steal fish from their neighbors. If you know your neighbor will go and hunt, your best strategy is to save your energy, wait for your neighbor to return with a fish, and steal it.... but you don’t know. The neighbor is making the same assessment of you. So the “evolutionarily stable strategy” is for both to hunt and both to steal when they can, even though the payoff for hunting + stealing is less than for just stealing. tern B hunts tern B hunts & steals tern A hunts each tern gets two fish, but high energetic cost tern A gets zero fish tern B gets two fish tern A hunts & steals tern A gets two fish tern B gets zero fish Each tern gets one fish