Chapter 6 Behavioral adaptations for survival

1. Chapter 6 Behavioral adaptations for survival • Evolutionary success is measured in offspring produced or genetic contribution to the next generation, but to reproduce it is necessary to survive long enough to do so. • Consequently, organisms have evolved a diverse variety of strategies to enhance their ability to avoid or deter predators.

2. Anti-predator strategies • Defensive adaptations include: • Predator avoidance • Hiding and camouflage • Group defense • Fleeing • Signal unprofitability • Warnings, deception and honest signals

3. Costs and benefits of camouflage • Many organisms avoid predators by the use of cryptic coloration. • A requirement of camouflage in many cases is that the individual choose an appropriate background.

4. Peppered moths • Classic example of evolution in action is that of the peppered moth, which occurs in two forms a typical white/speckled form and a melanic or black form. • In early 1800’s dark form very rare. • Dark form caused by dominant mutation that occurs spontaneously.

5. Peppered moths rest on trees and depend on camouflage for protection.

6. Peppered moth • In unpolluted areas trees are covered in lichens and the light form of the moth is hard to see. • In mid 1800’s air pollution in British cities covered trees with soot. • In cities dark form became common and light form rare.

8. Peppered moth • In mid 1950’s pollution controls were introduced in Britain and frequency of melanic form has declined since then.

10. Peppered Moth • Kettlewell carried out famous experiment in which he placed moths on dark and pale tree trunks and showed that background strongly influenced survival. • In wild, however, moths take much more care about where they settle and rarely settle on tree trunks.

11. Instead moths usually choose to rest in shady areas where branches join the trunk. • If moth’s choice of site is adaptive then moths in these positions should be taken less often by predators than those on tree trunks.

12. In an experiment in which dead moths were pinned to open tree trunks or the underside of branches birds consumed fewer of those on the undersides of branches.

13. 6.17

14. Other moths also make very specific choices about where to rest. • The whitish moth usually perches head up with its forewings covering its body. • When given a choice of resting site these moths prefer birch trees.

16. Pietrewicz and Kamil (1977) tested whether these chocies by moths were selectively advantageous. • Trained blue jays to respond to slides of moths by pecking a button for a food reward whenever they spotted a moth.

17. Results showed that blue jays spotted moths less often on birch trees and especially when moth was oriented with its head up. • Thus, moths choices appear to reduce the risk of detection by visually hunting predators.

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19. Costs and benefits of anti-detection behavior

20. Hiding from predators has costs. If you’re hiding can’t be doing something else.

21. Belding’s Ground Squirrels, trapped six days running. Held in trap and fed either peanut butter or lettuce. Lettuce eaters lost weight.

22. Subsequently, lettuce eaters when foraging less likely to stop feeding when predator alarm call made. Squirrels trade off risk of predation against need to feed.

23. Trinidadian guppies and predation risk Males must display to attract females. But, predators can spot them when they display.

24. A major predator is most active at high light intensities. Male guppies risk is increased in bright light. Expect males to reduce displays.

26. Big males most conspicuous and vulnerable. Expect large males to be most likely to cease displaying in bright light.

28. Vigilance and groups. Flocking and herding behavior widespread. Several potential advantages. 1. More eyes increase chance of predator detection. 2. Better defense in a group 3. Dilution effect

29. 1. More eyes increase chance of predator detection.

30. Experiments by Kenward using a trained Goshawk showed that as flock size increased woodpigeons detected an approaching bird at greater distances.

33. 2. Better defense possible as member of a group.

34. Many animals actively defend themselves against predators. E.g. Musk oxen form defensive circle facing outwards with calves on inside when attacked by wolves. Musk Ox

35. Wasps whose nest is disturbed swarm out and attack the intruder.

36. Sawfly larvae form clusters and defend themselves using drops of eucalyptus oil, which they regurgitate and apply to their enemy.

37. Many colonially nesting birds harass predators who enter the colony. E.g. Gulls and terns dive bomb intruders.

38. Such attacks are effective at deterring intruders. In experiment artificial nests placed in middle of colony less likely to be destroyed by predators than nests on the edge.

40. Non-colonial birds also “mob” predators. In mobbing behavior perched hawks and owls are surrounded by groups of birds that call loudly and harass the predator.

41. Mobbed bird often flies away to avoid harassment. Why does mobbed bird leave?

42. Probably because predator’s chance of catching prey is low once discovered by potential prey.

43. Mobbing a predator potentially is dangerous. Why do small birds take the risk?

44. Because mobbing may cause predator to move far away. European kestrels after being mobbed moved on average a distance more than twice the territory diameter of birds doing the mobbing.

45. 3. Dilution effect. Increasing group size reduces chance that a particularindividual will be chosen by a predator. E.g. bird in flock of 100 has only 1% chance of being picked by predator.

46. Extreme example of dilution effect seen in “swamping strategies” Many prey synchronize behavior in attempt to overwhelm predators ability to consume them.

47. E.g. Almost all Wildebeest give birth in about a 2-week period.

48. Hyenas and other predators cannot eat all the babies, so most survive.

49. E.g. Mayflies emerge to breed over a period of only a few days. Predation risk is lowest for those individuals that emerge with most others.