Feeding Behaviour

Question 1

feeding behaviour

Answer 1

• enables us to survive, gives us energy to grow and reproduce
• What is eaten (and how much, and when) is of critical importance for survival, health, and reproductive success (ie. We can’t eat too much)
• acted upon strongly by natural selection

Question 2

optimal foraging theory

Answer 2

• predicts that animals will make foraging decisions that are “optimal” and that maximize fitness of decision-maker
• energy gained should be much more than energy spent

Question 3

optimal foraging: crows and whelks

Answer 3

• crows eat whelks by picking up large whelks, flying 5m up, and then dropping them on the beach -> how do we know this is optimal foraging?
• large whelks need fewer drops, probability of breakage increases sharply until 5m
• Opening whelk costs them 0.5kcal but gives them 2.0kcal -> net gain of 1.5kcal (med or small whelks always give net loss)

Question 4

calorie maximization hypothesis

Answer 4

fitness benefit (calories obtained) should outweigh fitness cost (calories spent)

Question 5

problems with optimal foraging theory

Answer 5

• What if caloric intake is not the whole story?
• Many factors other than calories
• Crows living near bald eagles drop large whelks from less than 5m, even though they need to drop the whelks many times

Question 6

honeybee foraging

Answer 6

• How does a colony of specialized individuals maximize foraging to feed the entire colony?
• Interface between foraging and communication
• • Maximizing energy gained over energy spent
• • Dance communication -> returning foragers “dance” and others follow them closely in the dark
• • Longer dance = longer energy spent (usually longer distance) to get to food source

Question 7

honeybee dances

Answer 7

• The round dance – no directional information, food within 50m of hive
• The waggle dance – food is beyond 50m, returning forager communicates direction and distance of food
  – If done outside of hive, uses sun’s position to orient waggle run toward food
  – If done inside hive, deviation of waggle run from gravity = deviation of food from the sun (ex. 20 degrees to the right of
  vertical is 20 degrees to the right of the sun)

Question 8

von Frisch’s bee experiments

Answer 8

• Caught bees at feeding station, colour marked them, watched what they did when they returned to hive, and how others responded
• Put one open feeder at the hive, bee found it and returned to hive, then opened other feeders at different angles to hive to see how many went to original feeders vs. New feeders
• • Majority went to original feeder
• • Similar experiment done with feeders at different distances, same results

Question 9

cumulative selection

Answer 9

small changes accumulate over time; each step has to confer an advantage, even slight, or it won’t be selected for

Question 10

evolution of bee dances

Answer 10

• evolved due to cumulative evolution
• possible evolutionary sequence:
• • Simple agitated behaviour, recruits search for similar flower odor (direction)
• • Forager leaves scent trail (direction) and buzzes
• • Use of sound to indicate distance, short dance outside to indicate direction (distance and direction)
• – Sun (direction), x-axis (distance)
• • Waggle dance inside hive
• – Sun (direction), y-axis (distance)

Question 11

bee dances and convergent evolution

Answer 11

bees didn’t have common ancestor with those traits; developed independently

Question 12

human feeding behaviour

Answer 12

• Humans subject to same cost-benefit analysis of feeding behaviour
• Not adapted to deal with overabundance of processed foods (ie. sugar)

Question 13

adult brain and energy

Answer 13

• requires 20% of body’s energy, although it only takes up 2% of body mass
• Why is our brain so energy hungry?
• • Brain got bigger as humans evolved
• • Expensive tissue hypothesis: if overall consumption doesn’t increase, must compensate by diverting energy from other tissues (ex. Gorillas are bigger, but brains are smaller and need less energy -> with this diet, they could either have big body or big brain)

Question 14

how can we sustain our big brains and eat so little?

Answer 14

• cooking food! (raw food diet wouldn’t support us)
• • Kills pathogens
• • Reduces spoilage -> save food for longer -> less energy spent looking for it (less time spent foraging)
• • Increasing energy availability (only get 30-40% raw, almost 100% cooked)
• • Decreases energy used to digest
• Catch 22: in order to have a bigger brain, you need to cook food (but you need to be smart enough to cook it in the first place)

Question 15

mice moms and sugar study

Answer 15

• Mice moms given either glucose (fairly normal) vs. Sucrose (not good) during pregnancy
• Sucrose mom had way more fat droplets in liver (potentially dangerous levels)
• babies had to press lever increasing amount of times to get sugar pellets, looked for “break point” in motivation (where they decided it was no longer worth it)
• sucrose babies had higher break point (differences in motivation to gain access to sugar)
• Could be through this type of behaviour that obesity is passed down transgenerationally