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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 involves: • hiding • mimicry • camouflage 3 Leaf Mimicry 4 Biston betularia (camo moth) Question: What does the previous example (Figure 6.16 in the text) have to do with behavior? Ans: It prevents eating behavior by the predator! (but also moths must choose appropriate background) 6 DIFFERENT TYPES OF CAMOUFLAGE Background matching (like the moths) Countershading – common in fish and birds Edge Disruption Form Disruption 7 VENTRAL COUNTERSHADING EDGE DISRUPTION Which image is more readily identified as a snake? 8 FORM DISRUPTION (DISRUPTIVE COLORATION) Zebra salad Vertical stripes = vertical grass Predators often cue on eyes (an attack releaser) 9 Using an anti-predator behavior to discuss the testing of hypotheses about behaviors… 10 Skipper butterfly caterpillars eject feces from their hiding spots.... A wasp preys on the caterpillars. Are the caterpillars harder to find by the wasps if feces are not present? Hypotheses: Fecal ejection (FE) removes a chemical cue that helps the wasp find the caterpillar. Set up experiment where caterpillar hiding spots fitted with added feces or dummy feces. 11 Set up experiment where caterpillar hiding spots fitted with added feces or dummy feces. ? 12 Results: Wasps do visit fecal nests more often and for longer times. The wasp’s interest: Be careful of interpretation. Did we “prove” the hypothesis? The fact that the wasps prefer hiding places with feces does not prove the caterpillar’s behavior is a wasp anti-predator strategy that removes a chemical cue. Other possibilities: 1. FE could have evolved for another reason, but happens to also work against wasps. 2. FE could have evolved to evade a different predator, but happens to work against wasps too. 3. Another trait could have been selected for, but FE is linked to it. 4. FE could be an anti-predator strategy that has nothing to do with chemical cues. (Maybe FE is a way to shoot down wasps…) This beetle blasts away at ants! A better approach is to try and disprove a hypothesis. Hypothesis #2: FE is for hygiene, not an anti-predator mechanism. Testable! Add or subtract feces and measure health (e.g. growth rate of caterpillars. Turns out there is no health benefit. Reject hypothesis #2. Make strong statement that FE is NOT for hygiene. (Eventually eliminate all alternative hypotheses) 17 MULTIPLE SELECTION PRESSURES – cryptosis behavior vs advertisement… There may be more than one selective force leading to apparently maladaptive or conflicting behaviors. 18 Tungara frog (Physalaemus pustulosus) gives a variable advertisement call. If multiple males heard (= more male competition for females), frog produces a call more attractive to females. … but the more attractive call makes the male frog more vulnerable to predation. So males balance need to attract females with need to stay alive! The bat Trachops can more easily localize the frog when it gives the whine+chuck call, the call more attractive to females. Squirrels calibrate their anti-predator behavior against snakes using a cost-benefit analysis. The more threatening the snake, the less aggressive is the squirrel! Mobbing by rock squirrel 23 PARASITE-HOST BEHAVIORAL INTERACTIONS Deception is also prevalent with parasitehost interactions. Consider the famous case of Oropendolas and Cow birds... 24 Oropendola … and nest Cowbird Bot flies and a squirrel with an infestation. Deceptive signal I am not who I appear to be. By being cryptic: You didn’t really hear a frog… By appearing more fierce: Are you sure I am not dangerous to you? Intimidation mimicry The caterpillar Hemeroplanes ornata 29 A deceptive mimic -- The fly mimics the very predator that is after it. fly jumping spider Honest (non-deceptive) signals also can 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. 32 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… … but is it confusion or unprofitability? 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. Is this an honest signal of unprofitabilty? Again, must be careful about interpretation. Do we know if snakes can make such a judgment? Do we know if a lizard with more endurance has a greater ability to avoid snakes? Maybe push-ups are just the residue of excitement. SOCIAL INSECTS AND GROUP DEFENSIVE BEHAVIOR 40 Social learning of predators vs. innate fear Monkeys have no innate fear of snakes, but if they are shown a video of another monkey being afraid of a snake, then they become afraid of snakes, too even if they have never seen a real snake before. This is also true for spiders, but not for clowns. (How would the amygdala learn to recognize a clown? ) 41 Summary So we see that in some cases there are structural aspects to anti-predator strategies, and the use of these requires particular behaviors. Sometimes these behaviors are minimal. In other cases, there is just a behavior. Anti-predator strategies include: o being cryptic o being confusing o being intimidating – typically with a deceitful signal o communicating poor value with an honest signal o being in a collective o the value of avoiding predation has to be balanced by the 42 cost of not being available for feeding, reproduction, etc.