Chapter 8

Question 1

Research 8.1: Bees use Multiple Sense to Enhance Foraging Efficiency

Answer 1

a) All animals possess multiple sensory systems
b) Bees feed on nectar and pollen in flowers that differ in colour and shape, and odour

Question 2

BEES & MULTIPLE SENSES: Research Question

Answer 2

Is foraging more efficient when multiple senses are used?

Question 3

BEES & MULTIPLE SENSES: Methods

Answer 3

a) In a lab, a box was attached to the colony container
b) The box had a manual gate that allowed the researchers to release one individual at a time into the experimental arena
c) It contained eight artificial flowers, small circular wells with either 30% sucrose or water
d) During training, bees were exposed to two yellow flower shapes, circles or crosses, which surrounded the well
e) Bees were also exposed to two odours
f) There was three different treatments that varied in their cues associated with rewards
g) Training was deemed complete when an individual achieved 80% correct flower choices over the last 10 choices
h) Once trained, a bee enters the arena where all flowers are non-rewarding

Question 4

BEES & MULTIPLE SENSES: Results

Answer 4

a) Bees trained on two sensory modalities had significantly higher feeding performance than bees trained using only a single sensory modality
b) Two-modality bees made more correct choices and spent less time deciding where to feed
c) This suggests that the ability to use multiple sensory modes (vision and odour) facilitates efficient foraging in bumblebees

Question 5

Research 8.1: Grey Mouse Lemurs use Multiple Senses to Find Food

Answer 5

a) Grey mouse lemurs are very small nocturnal primates that feed on a variety of arthropods and fruits
b) Many small nocturnal mammals, like mice, rely on olfaction to locate pray while diurnal primates rely heavily on vision
c) Observations of wild mouse lemurs suggest that individuals might find insect arthropod prey both visually and by hearing their rustling movements
d) Given the diversity of sensory systems that grey mouse lemurs appear to use, they wanted to determine the relative importance of them all

Question 6

GREY MOUSE LEMURS & MULTIPLE SENSES: Research Question

Answer 6

How important are vision, hearing, and smell in prey detection by nocturnally foraging grey mouse lemurs?

Question 7

GREY MOUSE LEMURS & MULTIPLE SENSES: Hypothesis

Answer 7

Lemurs will detect prey more accurately with the use of multiple sensory modalities

Question 8

GREY MOUSE LEMURS & MULTIPLE SENSES: Methods

Answer 8

a) Used a choice test experimental design in which one mealworm was placed under one of two dishes, covered with cone lids
b) Manipulated sensory cues so that one, two, or three cues were present at each dish with food
c) Conducted experiments under low light levels, testing six lemurs on each treatment 14 times

Question 9

GREY MOUSE LEMURS & MULTIPLE SENSES: Results

Answer 9

a) Individuals used all three senses to locate prey successfully
b) Food detection probability increased with the number of sensory modalities used
c) Detection is the highest when a visual cue is present

Question 10

Research 8.2: Trout and Search Images

Answer 10

a) How do predators find difficult to locate cryptic prey?
b) Perhaps they learn a SEARCH IMAGE: the distinctive visual features of a single prey type
c) Brown trout often hunt diurnally and rely more on visual cues
d) They live in streams and are opportunistic feeders that eat a wide variety of invertebrate prey
e) Trout parr possess TETRACHROMATIC colour vision, meaning they have four different types of cone cells, allowing them to see in red, green, blue, and ultraviolet spectra, an ability that is thought to allow them to find cryptic prey

Question 11

TROUT & SEARCH IMAGES: Research Question

Answer 11

How does cryptic prey colouration affect trout predator foraging efficiency?

Question 12

TROUT & SEARCH IMAGES: Hypotheses

Answer 12

Prey that match their background will be harder for predators to detect, and predator hunting efficiency will increase with experience

Question 13

TROUT & SEARCH IMAGES: Methods

Answer 13

a) Established two test aquaria, identical except for the colour of the aquarium bottom: one was brown and the other was green
b) Placed a single prey (maggot) in one of six different locations on the aquarium bottom, the maggot was cryptic on the brown background and conspicuous on the green background
c) Recorded the amount of time until test fish found the food item
d) Tested 42 parr, half with cryptic prey and half with conspicuous prey

Question 14

TROUT & SEARCH IMAGES: Results

Answer 14

Individuals found non-cryptic prey faster than cryptic prey. Search times to find prey decreased with experience

Question 15

TROUT & SEARCH IMAGES: Conclusion

Answer 15

Background colour matching can benefit prey by reducing predator hunting efficiency. Predator search efficiency for cryptic prey can increase over time

Question 16

Optimal Foraging Theory

Answer 16

a) Assumes that natural selection has favoured feeding behaviours that maximize fitness
b) Many OFT models assume that fitness while feeding is a positive function of an individual’s energy intake rate
c) These models describe the relationship between possible behaviours and the fitness they produce
d) Optimal Behaviour: the behaviour that produces the highest fitness
e) These models provide ultimate explanations about the function of behaviour

Question 17

Diet Model

Answer 17

a) Animals encounter food types that differ in size, energy content, and handling time
b) Given this diversity, individuals need to decide which food items to eat and which to reject
c) The Optimal Diet Model has three assumptions: (1) foragers maximize fitness by maximizing energy intake rate, (2) food items are encountered one at a time and in proportion to their abundance, and (3) all food items in the environment can be ranked according to their profitability
d) Profitability: the energy it contains divided by its handling time
e) Generalist: a forager that eats a wide variety of food types
f) Specialist: foragers with restricted diets, only consuming a small subset of potential food types
g) Forager’s average energy intake rate per item = (average energy obtained/item) / [(average search time/item) + (average handling time/item)]
h) As more food types are added to a diet, the average search time per item declines
i) Results: the model predicts that a forager should always eat A, B, and C but reject D and E because the cost in handling time of including them in the diet is greater than the benefit derived from reduced search time
j) Zero-one Rule: each food type should always be accepted or always be rejected

Question 18

Research 8.3: Diet Choice in Northwestern Crows

Answer 18

a) Optimal Diet Model used to understand the feeding behaviour of Northwestern Crows
b) They eat mainly Japanese littleneck clams but often reject clams that they have found
c) Clams on the island range in size
d) They open clams by dropping them onto rocks repeatedly to break them and then pry open the shells with their bills
e) Needed to measure handling times, the energy content of the clams, and encounter rates (search times)

Question 19

CROWS & DIET CHOICE: Research Question

Answer 19

Why do Northwestern Crows reject some clams while foraging?

Question 20

CROWS & DIET CHOICE: Hypothesis

Answer 20

Crows attempt to maximize energy intake rate according to the optimal diet model

Question 21

CROWS & DIET CHOICE: Methods

Answer 21

a) They observed crows feeding on clams of different sizes and recorded the time from the first drop until the clam was eaten (handling time)
b) Then they collected the empty shell to determine its size to see how handling times varied with clam size
c) Second, to increase their sample size and obtain handling time data on clams of all sizes, they dropped over 500 clams of different sizes onto rocks from heights similar to those used by crows
d) They measured the number of drops it took until the clam could be pried open with a fingernail
e) To measure energy content, they collected and dried the soft tissue from 100 clams of different sizes, they found that energy content and handling time both increased with clam size
f) They assumed that clams of different sizes represented different food types
g) They collected data on the abundance (encounter rates) of each clam size

Question 22

CROWS & DIET CHOICE: Results

Answer 22

a) The model predicted that crows should eat all clams greater than 29mm and reject all clams less than 29mm to maximize energy intake rate
b) They found that crows almost always ate clams that were larger than 30mm and always rejected clams that were less than 26mm
c) However, crows did not follow the zero-one rule, sometimes eating clams of intermediate size
d) The crows’ behaviour was quite similar to the predicted behaviour

Question 23

Research 8.3: Ant Foraging and the Effect of Nutrients

Question 24

ANTS’ FEEDING BEHAVIOUR & SODIUM LIMITATION: Hypothesis

Answer 24

Sodium limitation affects the feeding behaviour of ants

Question 25

ANTS’ FEEDING BEHAVIOUR & SODIUM LIMITATION: Predictions

Answer 25

a) They examined the recruitment of ants to two food baits: sucrose and sodium chloride
b) Hypothesized that to maximize energy acquisition, ants would recruit heavily to sucrose
c) However, if sodium is limited and essential, ants should also recruit heavily
d) They predicted that ants living far from salted roads would prefer NaCl baits than ants living nearer to salted roads

Question 26

ANTS’ FEEDING BEHAVIOUR & SODIUM LIMITATION: Methods

Answer 26

a) Established two sets of transects that ran parallel to a road that was salted during the winter
b) Each set had four transects located 1, 10, 100, and 1000m from the road
c) At 1m intervals along each transect, the researcher placed a single 2 mL vial on the ground that was half-filled with either sucrose or NaCl

Question 27

ANTS’ FEEDING BEHAVIOUR & SODIUM LIMITATION: Results

Answer 27

a) NaCl concentrations were about ten times higher 1m from the road compared to all other distances, indicating that road salt application does increase sodium availability near roads
b) Near the road, these ants strongly recruited to vials containing sucrose
c) As distance from the road increased, ant use of NaCl vials also increased
d) Sodium limitation affects the feeding behaviour of these ants, illustrating how nutrient requirements can affect diet choice

Question 28

Optimal Patch-Use Model

Answer 28

a) Predicts how long a forager should stay in a food patch to maximize its fitness
b) Based on four assumptions: (1) foragers attempt to maximize energy intake rate, (2) all patches are identical, (3) travel time between patches is constant, and (4) as a forager depletes a patch, its instantaneous harvest rate declines, experiencing diminishing returns
c) Marginal Value Theorem: predicts that a forager should stay in a patch until its marginal benefit of feeding declines to equal the average energy intake rate from the environment
d) Calculated by dividing the total energy acquired from all patches by the total time to travel to and then exploit the patches
e) The model predicts the amount of time a forager should spend in a path for any fixed travel time, this number depends on the travel time: as travel time increases, foragers should spend longer in each patch

Question 29

Research 8.4: Patch Use by Ruddy Ducks

Answer 29

a) They feed on aquatic invertebrates and vegetation on muddy lake bottoms
b) They repeatedly dive from the water’s surface to the lake bottom to find food

Question 30

RUDDY DUCKS & PATCH USE MODEL: Results

Answer 30

a) The harvest rate did indeed decline as ducks depleted the patch: the cumulative gain curve is steep when a bird enters the patch and levels off as the patch becomes depleted
b) In the second experiment, he found that the model accurately predicted patch use for the majority of ducks, concluding that most of the ducks were maximizing energy intake rate

Question 31

Optimal Patch Model with Multiple Costs

Answer 31

a) A new model that includes the energetic costs of foraging, predation risk costs, and missed opportunity costs
b) Energetic Costs of Foraging: include the energy used to exploit a patch and the metabolic costs incurred while feeding
c) Predation Risk Costs: involve the probability of being killed while feeding
d) Missed Opportunity Costs: the costs of forgoing other activities that might yield even higher fitness
e) Model predicts that if two patches have the same food and same costs, they should be harvested down to the same food density
f) This prediction holds even if patches differ in their initial food density

Question 32

Research 8.4: Fruit Bat Foraging on Heterogeneous Patches

Answer 32

a) Brown’s model predicts that patches will be harvested down to the same food density, regardless of initial food density, if foragers are maximizing their energy intake rate
b) Examined the behaviour of captive bats that exploited artificial feeders in a large outdoor flight cage

Question 33

FRUIT BATS & PATCH USE: Research Question

Answer 33

How do fruit bats exploit food patches that differ in initial food amount?

Question 34

FRUIT BATS & PATCH USE: Hypothesis

Answer 34

Bats will attempt to maximize their energy intake rate

Question 35

FRUIT BATS & PATCH USE: Methods

Answer 35

a) They housed bats in an outdoor flight cage that contained feeding stations
b) Each station contained three artificial feeders that differed only in the amount of food they contained
c) Recorded giving-up densities in all feeders each day for three days

Question 36

FRUIT BATS & PATCH USE: Results

Answer 36

Bats experienced diminishing returns when using the feeders, they equalized the giving-up densities of the three feeders at each station

Question 37

FRUIT BATS & PATCH USE: Conclusion

Answer 37

Bats maximize their energy intake rate when feeding on patches that differ in initial food amount

Question 38

Research 8.4: Kangaroo Rat Foraging with Variable Predation Costs

Answer 38

a) If foraging benefits are the same but costs differ between two patches, foragers should spend less time at the patch with higher costs, leaving it with a higher GUD
b) Nocturnal, seed-eating Kangaroo Rats
c) In the desert, individuals can search for seeds under shrub canopies or in the open between shrubs
d) They examined how fresh urine scent affected patch use by kangaroo rats feeding either under shrubs or in the open

Question 39

KANGAROO RATS & PATCH USE: Methods

Answer 39

a) Established 48 pairs of standardized food patches filled with sand and a fixed amount of seed
b) In each pair, one tray was placed under the canopy of a creosote bush and another was placed 4m away in the open
c) Next to each tray was a dowel that they’d add the scent of a predator to
d) Trays either had no urine, both had urine, or only one had urine

Question 40

KANGAROO RATS & PATCH USE: Results

Answer 40

a) They exhibited a preference for feeding at the shrub tray when predator scent was found at both trays, at neither tray, or only at the open tray
b) However, when predator scent was present only at the shrub tray, they no longer preferred to feed there
c) These Kangaroo rats perceive lower foraging costs (predation risk) under shrub canopies, except when predator urine is present only at the shrub

Question 41

Research 8.4: Bayesian Foraging Bumblebees

Answer 41

a)

Question 42

BUMBLEBEES & BAYESIAN FORAGING: Methods

Answer 42

a) Made artificial flowers using micro-centrifuge tubes that contained either sugar water or water
b) Created a foraging arena that contained ten food patches, with 12 artificial flowers
c) They trained individual bees to learn different distributions of patch types
d) This information became the bee’s prior knowledge
e) The location of the rewards was randomly assigned within each patch so bees could not memorize the exact location within patches
f) Patch variance in this distribution of patch types was zero
g) Predicted that the patch quality estimate of bees trained should decline each time the bees found a food reward since this indicated the presence of one less food reward

Question 43

BUMBLEBEES & BAYESIAN FORAGING: Results

Answer 43

a) Bees trained in the uniform environment had a lower probability of staying in the patch for each reward found
b) Bees in the high-variance environment showed a much higher probability of remaining in the patch after finding the second reward
c) The likelihood of patch departure did not decline for each reward found thereafter
d) They display adaptive learning regarding the distribution of resources in their environment

Question 44

Research 8.5: Spice Finch Producer-Scrounger Game

Answer 44

a) Some individuals within stable social groups often take food from conspecifics
b) Producers: individuals that search for and find food
c) Scroungers: those that usurp food from producers
d) As the proportion of scroungers increases in a group, fewer scrounging opportunities will exist

Question 45

SPICE FINCHES & PRODUCER/SCROUNGERS: Methods

Answer 45

a) Producer-Scrounger Game Theory Model was developed
b) It assumes that searching for and finding food is incompatible with searching for scrounging opportunities
c) Model assumes that the feeding rate (fitness) of scroungers decreases as the frequency of scroungers increases
d) Predicts that there is an equilibrium frequency of scroungers and producers at which their fitness is equal, meaning both behavioural strategies can persist

Question 46

SPICE FINCHES & PRODUCER/SCROUNGERS: Results

Answer 46

a) Feeding rate for scroungers was indeed lower when patches were covered
b) As expected, for both uncovered and covered patches, the feeding rate of scroungers declined as the proportion of scroungers increased
c) The feeding rate of producers was largely unaffected by the proportion of scroungers for both types of patches
d) For uncovered patches, producers and scroungers had equal fitness when they were equally common; for covered patches, scroungers and producers had equal fitness when a flock had one scrounger and five producers
e) In another experiment, individuals tended to adopt one or the other foraging strategy, although there was some switching of patch sides at the start
f) In a few days, flocks adjusted their scrounger frequency to the predicted values