Lesson 11: Foraging Behavior pt. 2

Question 1

the concept of optimality

Answer 1

• this is the simple idea that there may be more than one way to accomplis a goal AND one of those ways just might be better than others, In other words, it is the OPTIMAL WAY
• IF in fact there is an optimal way AND it is heritable, then the optimal way should be selected for and the suboptimal ones should be selected against (even though they work to achieve the tsak)
• so the animal’s behavior should get sculpted by natural selection to be OPTIMAL

Question 2

optimality theory - rufous hummingbird migration - finding th eoptimal territory size

Answer 2

chart with 3 columns: day, territory size, and weight gain
- most weight gain came from the medium sized territories

Question 3

optimal foraging theory

Answer 3

in a model, we make assumptions about how things work, them we tru to figure out what logically follows from those assumptions in the hope that will help us choose what kind of studies to do

optimal foraging ttheory – assumes natural selection has favored feeding behaviors that maximize fittness (optimal behaiors)

• many optimal foraging moels assums that fittness inreases with energy intake rate ( that is the more calorie the animal can find the better , because it will funnel excess energy into reproduction)
  —- BUTTT also need to include the cost spent to obtain the energy so models look at some measure of the beneift - cost = net benefit

Question 4

the optimal diet model

Answer 4

tried to figure out what decions animals should make when selecting food items to eat. The model assumes:

• foragers maximize fittness by maximizing net energy intake rate
• food items are encountered one at a time in proportion to their abundance
• food items can be ranked by their profiability

Question 5

profitability

Answer 5

= energy/handling time

Question 6

handling time

Answer 6

= time to manipulate item prior to consumption

Question 7

in the table, if various foods have the same energy but different handling times (s), then

Answer 7

(J/S) is better with shorter handling times
J = joules

Question 8

specialists

Answer 8

using only a few types of food

Question 9

generalists

Answer 9

using most types of food

Question 10

in addition to handling time, you also need to consider ()

Answer 10

search time (that is the information is about abundance)

Question 11

apple snails - optimal diet

Answer 11

• few animals eat apple snails because they are large, hard to handle, and can seal themselves up with a trapped door (an operculum)
• Snail kites have adaptations which will change handling time
• have hooked beaks and huge talons ideal for opening apple snails
• are apple snail specialsists

Question 12

foraging by nrothwestern crows for WHELKS

Answer 12

northwester crows are generalists that feed on a lot of things, but have a specialized way of breaking shellfish aling the rocky shores of the pacific northwest – they drop shells onto hard surfaces in order to break them

1.) crows are picky – often skipping over severla whelks before selecting one

2.) once they start working on a shell, they don’t quit and try to find a different shell to break

3.) all the crows flew up to about the same height and dropped shells from about 5 meters

Question 13

tested to see if crow’s preferences were based on the size of the whelk

Answer 13

all whelks were gathered from the study beach and divided into size classes, then equal numbers were laid out on the beach and the numbers remained after several hours were counted

results:
Crows prefer large whelks and reject small ones

NEXT
- they dropped actual shells from various heights to determine how hard it was to open them
- they found that a preferred large whelk always had a 25% chance of breaking
—- explains why crows don’t give up and fetch another whelk – the new whelk would have same chance of breaking

Question 14

graph for whelk

Answer 14

• the graph shows that large whelks are the easiest to break and that the optimun height for dropping is about 5 m - which is the eight crows usually drop them from

Question 15

energy budget for the crows

Answer 15

crow’s trip to the beach – it costs 553 calories to break one large whelk

benefit for one large whelk: 1490 calories (so net is 937 calories)

a medium whelk is harder to break (cost = 900 calories) and the benefit is only 600 calories, so net is -300

Question 16

nutritional constraints – moose

Answer 16

• moose typically feed on low-salt grasses and shrubs
• moose periodically seek out salt aquatic plants (even though they are low in energy)

Question 17

ant foraging: the effect of nutrients

Answer 17

• for the northern populations of the ant, Tapinoma sessile, salt can be a limiting nutrient
  – they can get their salt from road salt put down in winter – the salt leaches from the road into the surrounding areas; but note – further way from the road, less salt there is

Question 18

ant foraging experiment

Answer 18

• examined recriutment to food vials by Tapinoma sessile along 4 transects
• half of the vials contained sucrose, half contained NaCl
• transects were 1, 10, and 1000 m from a road that was salted with NaCl each winter
• recorded the number of sucrose and NaCl vials that contained ants along each transect

RESULTS:
- close to the road, less than 10% of vials visted by ants were salt vials
- ants recruited to salt vials more strongly as distance to the road increases – even though those vials had less energy

Question 19

nurtirional constraints: tassel-eared squirrels

Answer 19

often reject many similar trees before accepting one; why spend so much energy??

– need to avoid a toxic compound called alpha-pinene

Question 20

chacma baboons: predation constraint

Answer 20

chacma baboons pass through high value foraging and choose the medium value ones instead.. WHY?

• there is risk associated with high-value areas

Question 21

salmon: competition and predation

Answer 21

• baby salmon are predators of insects by are prey for larger fish
• a brown trout- typical predator of baby salmon

Question 22

salmon competition and predation experiment

Answer 22

method for determining how much risk a baby salmon will take to get a fly: basically the bigger the fly, the bigger the risk the salmon will take

• can stimulate a predator by placing a picture of a brown trout against the glass of the tank
• can stimulate a competitor by holding a mirror up against the glass of a tank

RESULTS:
the baby trout will take a bigger risk the bigger tje fly is
AND the distance traveled: with competitor > normal > with predator

Question 23

optimal patch-use models predict how long an animal should use a food patch before moving on

Answer 23

• basically animals using a food patch reap DIMINISHING RETURNS as they use up the food patch
  – that is, when a forager enters a food patch, it initially harvests food at a high rate - but as the patch is depleted, its harvest declines
  – the decision to move on or not should logically depend on the value of staying at the patch versus the difficulty of finding a new patch

Question 24

patch use by fruit bats

Answer 24

• fruit bats are dinural animals than feed on fruit and nectar. in this study, researchers designed a feeder that provided diminishing returns - much like a patch of food in real life
• the researchers stimulated “diminishing returns” by placing bits of rubber in the feeder
• as the fluid was drawn down, the rubber started clustering around the feeding tube and made it harder to suck out the nectar
• the graph shows that the total amount of food harvested increases with time in the patch - as you would expect
  ‘BUT
• the rate of that increase slows down with time indicating that there were diminishing returns

Question 25

patch use by fruit bats experiment

Answer 25

bats in an outdoor flight cage were given 3 identical feeders that contained a protein-sugar mix, but the concentration of sugar was different in all 3 feeders
low, medium, and high

Graph

• shows that the bats quit using feeders at about the same GUD (giving up density), that is, when each one had about the same amount of sugar remaining in the feeder, (so in lower concentrations there was more liquid left)
  THUS
• the reward per feeding attempt would be the same

Question 26

conclusion for the bats

Answer 26

• illustrates a major finding in patch use research: animals need a certain level of reward to keep on using the same patch
  – if the reward is too low, then they “give up” and move to another patch
  – since the GUD was the same in all 3 feeders, it seems that the individuals agree on what the minimum rewrds is. — suggests that the animals optimize their behavior

Question 27

bayesian foraging in bumblebees

Answer 27

can bumblebees estimate food patch quantity in a bayesian mannar? (biernaskie, walker, and gegear 2009)

^^ that is – do they use prior knowledge to make decisions about patch use? Bayesian implies use of prior knowledge

Question 28

bayesian foraging experiment

Answer 28

• bumblebees were trained to forage from artificial flowers offered in patches
• half of the bees trained in a uniform environemnt (5 pf the flowers had nectar in each patch)
• half in a “high-variance) environment (1 or 9 of the flowers had nectar in each patch)

RESUTLS
- bees trained in the uniform environment had a low propensity to stay in one patch
- after a bee finds one “flower” it knows 4 out of 11 flowers remain (36%) so it then finds a second, so then there are 3 out of 10 left (30%), then 2 out of 9, then only 1 out of 8

^^ so for these bees, the other patches with 5 out of 12 (42%) rewards would be “richer”

• bees trained in the high variance environment had a higher propensity to stay in one patch
  – after a bee found a “flower” it knows there are either none or 8 more – if it finds a second flower then it knows that there are definatrly 7 out of 10 more flowers (70%), then 6/9… and so on

Question 29

what does bayesian refer to

Answer 29

using prior knowledge