Chapter 6

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Department
Biological Sciences
Course
BIOC54H3
Professor
Maydianne Andrade
Semester
Winter

Description
Chapter 6 Darwinian Puzzles • Some species make it known to themselves to predators o Traits that seem to exceed their benefits are darwnian puzzles • Monarch butterfly: orange and black spots make it easy to spot o Monarch larvae feed on poisonous milkweed o Dead individuals educate predators so genetically similar monarchas pass on shared genes to the next generation o Alternative hypothesis: monarchs are so bad tasting that birds will release monarch after grabbing it • Ephritid fly: waves banded wins as if trying to catch the attention of predators o Wing markings resemble the legs of jumping spiders (fly predators)  Wing movement produces a similar effect to spides o Test hypothesis o Swap wings with clear-winged houseflies  Clearwinged mutants got eaten  Houseflies got eaten – combo of pattern and wing movement • Thomson’s gazelle – stotting: leap into the air o To scan ahead for unseen enemies lying in ambush o Anti-ambush hypothesis: stotting does not occur in short grass but reserved for tall grass habitats  However, short grass gazelles stott o Alarm signal hypothesis: warn others that predator is near o Social cohesion: stotting enables gazelle to form groups and flee in a coordinated manner to make it hard to cut them o Confusion effect: individuals confuse and distract following predators o Pursuit deterrence: announce to predator individual is in good health and is unlikely to be captured o Single gazelles stott – eliminate signal hypothesis – no need to warn  Eliminate confusion hypothesis: does not confuse  Social cohesion theory: should head towards other gazelles, but the rump is towards predators • Announce to predator they are hard to capture o Comparative method: look at other species that stot o Honesty of method of uncatchability  Anolis lizard: push up display when it spots a snake • Time spend running was correlated with push ups done • Moth – produces loud ultrasonic clicks when the muscles pull the tymbals in o Bats can hear ultrasound o Other moths are poisonous  Bats associate clicking with poison o Egle does not have to invest in metabolic equipment to store toxic but can still educate bats with acoustic deception • Birds and rabbits – calls while in crutches of predator o Perhaps product of ability to feel pain o Scream may startle a predator to release its prey  However birds continue to scream long after caught o Screams may warn of danger  However, members of species ignore – if predator is occupied, then no risk for others o Capture animals scream to attract other predators to the scene  Confusion model – to enable prey to escape  Attract-competing predator hypothesis predict that birds in dense cover give more screams than open habitats • Dense cover require calls for others to locate  Sounds convey health and condition of the caller • Distress call show health to suggest whether recapture is likely to reevaluate catching it in the first place Optimality Theory and Antipredator Behaviour • Fitness costs and benefits o Net benefit of a trait rather than whether or not a trait provides a benefit  Adaptation has more to do than merely confer a benefit o Adaptation is better than alternatives – better = net benefit is greater than nonadaptive features • Optimality Theory o Adaptation = greatest benefit  Optimal trait o Strongly used in foraging behaviour since it is possible to measure both costs and benefit in the same units – calories from food vs. calories expended • Antipredator behaviour o Bobwhite quail in groups of coveys 2-22 – peak at 11  Covey are safer from attack (higher overall group vigilance)  Benefits are offset by competition for food • Large group move more than groups of 11 o Small groups move even more to find groups of 11 Chapter 7 • Animals are good at postponing their demise, so predators have to overcome a series of obstacles to get to food o Hunting skills are the product of pretty defenses Optimal Foraging Behaviour • Crows: clam, snail, mussel, whelk – picks it up into the air and drops it to eat exposed eat o Foraging crows have certain behaviours  Whelks only 3.5-4.4 cm long  Fly up to about 5 meters  Kept with chosen whelk until it broke o Predictions for observed behaviour  Large whelks are more likely to shatter  Drops less than 5 meters yield a reduce break rate  Probability of whelk breaking is independent of the times it has already dropped o Predictions tested  Large whelks required less 5 meter drops before breaking vs. medium or small ones  Probability of whelk improves as the height dropped, but beyond 5 meter does not increase  Probability of breaking a whelk is not better after on next attempt – finding new pray requires more energy  Net calorie gain of big whelk – 1.5 kilocalories, medium whelk is a net loss of 0.3 kilcalories • Fitness as a function of energy gained per unit time • Zebra finches: highest daily net caloric gains survived best o Decrease seed intake take longer to lay their first egg • Sandpiper: need horseshoe crab for food o Over harvest of horseshoe crab led to decline of population  Those that survive the migration are heavier to start to secure fat stores for later How to Choose an Optimal Mussel • Oystercaster: optimal calculation: bigger mussels should provide more net caloric gain – but they do not prefer the really large ones o Hypothesis 1: profitability of large mussel is reduced because some cannot be opened which reduces average return  However, optimization should be at 50mm mussels but 30-45 is more preferred. o Hypothesis 2: large mussels are covered with barnacles which makes them impossible to open  Larger mussels has higher chance to acquire impenetrable coats of barnacle • Prey opening time
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