Behavioural Adaptations for Survival cont. and Evolution of Feeding Behaviour

1. Behavioural Adaptations for Survival cont.andEvolution of Feeding Behaviour BIOL 3100

2. Tephritid flies habitually wave their banded wings as if trying to attract the attention of predators. Any guesses as to why?

3. One possibility is that the wing markings resemble the legs of jumping spiders (important fly predators). The visual effect may be similar to the aggressive leg-waving displays in the spiders. Thus, flies may be using sensory exploitation to induce escape behaviour in the predator.

4. Feeding

5. Novel feeding behaviour in crows

6. Observation: Northwestern crows pick up large whelks (3.5-4.4cm) Fly up 5m to drop the chosen whelk Crows keep trying with the chosen whelk until it breaks

7. What is the optimal solution? Optimal foraging theory states that crows should behave in an optimal (fitness-maximizing) manner. If optimal,we can hypothesize: • Large whelks should be more likely than small ones to shatter after a drop of 5m • Drops of less than 5m should have lower breakage rate. Drops of more than 5m should not greatly improve chances of breakage • Probability that a whelk will break should be independent of number of times it has been dropped

8. 15m Drop whelks from a bunch of different heights and see if these predictions hold 10m 5m

9. 15m Large whelks take fewer drops and have a much higher caloric content Large whelk: 0.5kcal to open, 2.0kcal gain(net gain of 1.5kcal) Medium whelk: net loss of 0.3kcal 10m 5m Assumption: More calories ultimately results in increased fitness

10. Example 2: Oystercatchers

11. Observation: Eurasian Oystercatchers eat mussels that are smaller than the prey available. Optimality would suggest that they should be eating the largest possible mussels.

12. Hypothesis 1: Profitability of very large muscles is reduced because some cannot be opened at all, reducing the average return from handling prey Pure optimality Optimality with the consideration that large muscles must be abandoned after attack because they are impossible to open

13. Hypothesis 1: Profitability of very large muscles is reduced because some cannot be opened at all, reducing the average return from handling prey Problem is that the numbers don’t match. Oystercatchers are still taking prey 35-45mm instead of the 50mm they should be taking.

14. Hypothesis 2: Large mussels are not even worth attacking because they are covered in barnacles, which makes them impossible to open. So, our optimal solution didn’t fit reality. We refined the model (added the fact that really large mussels are impossible to open), but still didn’t fit. Finally, looked more closely at the ecology of the system (mussels cover big shells) and refined the optimality model again – and it worked!

15. How is feeding behaviour influenced by the presence of predators?

16. Dugongs alter their foraging tactics when dangerous sharks are likely to be present. Time spent excavating sea grass declines in relation to the probability that tiger sharks will be present.

17. Indirect effects from predators can also influence reproductive output. After wolves were re-introduced to Yellowstone, elk spent more time foraging in woodlands than in exposed meadows, resulting in decreased calf production and decreased calf survival.

18. Game theory and feeding When two or more distinctive phenotypes are present (e.g., garter snakes and slug-eating), we can ask why the type associated with higher fitness hasn’t replaced its rival over evolutionary time.

19. Feeding tactics can also be subject to frequency-dependent selection When resources are scarce for fruit fly larvae, the fitness of a sedentary sitter (red line) versus a wandering rover (purple line) depends on which of the two types is rarer.

21. Proportion of sinistral forms oscillates around 0.5 because whenever it is more common, it is selected against (and then becomes less numerous); whenever it is rarer, it becomes selected for

22. In spiders, web crypsis is presumably an advantage. If so, why do some orb-weaving spiders incorporate four thick, conspicuous, zigzagging lines of UV-reflecting silk which radiate out from the central resting point?

23. In spiders, web crypsis is presumably an advantage. If so, why do some orb-weaving spiders incorporate four thick, conspicuous, zigzagging lines of UV-reflecting silk which radiate out from the central resting point? Hypothesis 1: Decorations act as lures (sensory exploitation?), drawing victims into the webs Hypothesis 2: Spiders are actually dealing with their predators and the zigzags obscure the spider’s body or make the spider look larger and more dangerous

24. In spiders, web crypsis is presumably an advantage. If so, why do some orb-weaving spiders incorporate four thick, conspicuous, zigzagging lines of UV-reflecting silk which radiate out from the central resting point? Hypothesis 1: Decorations act as lures (sensory exploitation?), drawing victims into the webs Hypothesis 2: Spiders are actually dealing with their predators and the zigzags obscure the spider’s body or make the spider look larger and more dangerous