1
Q
how do visual predators find cryptic prey effectively?
A
- by learning a search image
2
Q
what does a search image favour?
A
- the evolution of behavioural and morphological adaptations in prey to avoid detection
- counteradaptations in predators to better detect hidden or cryptic prey
3
Q
what is an evolutionary arms race?
A
back-and-forth process of adaptation and counter-adaptation in two species
4
Q
what do optimal foraging theory (OFT) models assume?
A
fitness while feeding increases with energy intake rate
5
Q
what is the behaviour that maximizes fitness called?
A
optimal behaviour
6
Q
what are the two well-known OFT models?
A
- diet model
- patch-use model
7
Q
what does the diet model assume?
A
- foragers maximize fitness by maximizing enerhgy intake rate
- Food items are encountered one at a time in proportion to their abundance
- foot items can be ranked by their profitability
8
Q
what is the formula for profitability?
A
energy/handling time
9
Q
what is handling
A
time to manipulate item prior to consumption
10
Q
what is the average energy intake rate/time formula?
A
(average energy obtained/item)/[(average search time/item)+(average handling time/item)]
11
Q
what are diminishing returns?
A
when a forager enters a food patch, it initially harvests food at a high rate, but as the patch is depleted, its harvest rate declines
12
Q
what does the optimal patch-use model assume?
A
- foragers attempt to maximize energy intake rate
- all patches are identical
- travel time between patches is constant
- the instantaneous harvest rate declines as a forager depletes a patch; the forager experiences diminishing returns in each patch
13
Q
what is the marginal value thereom?
A
for a fixed travel time, Tt, energy intake rate is maximized when the forager spends Tp time in patch
14
Q
what are the costs of the patch-use model?
A
when feeding, animals experience: energetic costs, predation risk costs, missed opportunity (food item missed out in patch) costs
15
Q
what changes does Brown’s updated patch-model have?
A
- incorporates costs
- model predicts that patches w/identical benefits and costs should be harvested down to the same quitting harvest rate
16
Q
what is give-up density?
A
the amount of food remaining in a patch after foraging
17
Q
what is the incomplete information and food patch estimation?
A
- optimal patch-use model assumes animals know the quality of encountered patches
- however, many foragers will need to estimate the quality of food patch
- animals can combine sample information from a patch w/prior knowledge about the distribution of patch types using the environment, using Bayesian estimation
18
Q
what do animals use when searching for food?
A
several sensory modalities
19
Q
what sensory modalities does natural selection the most?
A
sensory modalities that most efficiently and effectively provide information about the location of food
20
Q
what do fish used to detect their body position, and info about water pressure or movement?
A
mechanoreceptors
21
Q
what is a lateral line system?
A
used by fish for hearing, for detecting their body position and for info about water pressure or movement
22
Q
what is hydrodynamic information?
A
info about water always changing
23
Q
what does velocity describe?
A
the speed and direction of an object’s motion
24
Q
what does acceleration measure?
A
how the velocity of an object changes overtime
25
what is a lateral line system composed of?
neuromasts
26
why does the hunting success of gray mouse lemurs increase as more modalities they use?
use of all 3 sensory modalities provides complementary sensory information under a variety of environmental conditions
27
explain the gray mouse lemurs sensory modalities to find food experiment
- wanted to see the importantance of visual, acousti and olfactory cues in foraging behaviour
- had 2 plates, one w/mealworm one w/o
- covered with cone lids
- manipulated so that one, two or 3 sensory cues were present at the dish w/food
- did in low light conditions bc are nocturnal animals
- results showed when could use all 3 sensory modalities, greatest success in locating prey
- detection highest when visual cue present
- use vision, olfaction and hearing to locate prey
28
define search image
the distinctive visual features of a single prey type that, once learned, can enhance prey detection
29
what are juvenile brown trout called?
parr
30
describe juvenile trout
- hunt diurnally (heavily rely on visual cues for foraging)
- are opportunistic feeders and eat wide variety of invertebrate prey
- often have to learn to search for new prey as soon as become available bc of different emergence times of aquatic invertebrates over the year
- have ability to distinguish colours - thought to be adaptation that allows animals to find cryptic prey
31
conspicuous vs cryptic prey
conspicuous - clearly visisble
cryptic - camouflaged
32
explain what it means to say food is typically heterogeneously distributed in environment
most places have little food, while food patches may contain lots
32
define optimal foraging theory (OFT)
an approach to studying feeding behaviour that assumes that natural selection has favoured feeding behaviours that maximize fitness
33
define optimal behaviour
the behaviour that maximizes fitness in an optimal foraging theory model
34
what type of explanation do OFT models provide?
ultimate explanations - evolutionary
35
why are OFT models used?
produce testable predictions that can be applied to many species and behaviours
36
define profitability
for a food item, the energy it contains divided by the handling time - higher profitability means higher-ranked food item
37
define generalist
a forager that consumes a wide variety of items in its diet
38
define specialist
a forager that has a narrow diet
39
what is the average search time per food item?
rate at which an individual encounters food in the diet
40
explain the diet choice in northwestern crows experiment
- used optimal diet model to understand why crows often reject clams that they have found
- needed to measure: handling times, energy content, and encounter rates (search times for each item) for clams
- measured handling times of different sized clams two ways; 1- measured time from first drop of clam to until it was eaten (defined as handling time), 2 - dropped dif. sized clams from similar height and measured # of drops until clam could be easily opened
- measured energy content of clams based on amnt of dry tissue from clams
- found energy content and handling time increased w/clam size, largest clam was most profitable, and profitability declined as size declined
- measured availability of dif. sized clams in specific quadrants to determine the encounter rate for each clam size
- model predicted crows to eat clams of specific size and reject those smaller than specific size to maximize energy intake
- colected data on clams being eaten and rejected by crows; saw crows did not follow zero-one rule, but had partial preference (sometimes ate clams of intermediate size)
- concluded diet model does not predict partial preferences, but does predict behaviour similar to exhibited behaviour
41
what are some explanations as to why animals exhibit partial preferences for some food types?
- model assumes foragers have perfect knowledge of abundance of food types and energy content and handling time of each type
- model assumes that there are no competitors and no predation risk
- these factors can lead animals to modify diet in ways that exhibit partial preferences
42
how do many herbivores fulfill sodium limitation?
are attracted to natural or artificial mineral licks that contain sodium
43
why do many herbivores have a lack of sodium?
plants contain low sodium concentrations
44
explain the ant foraging and the effect of nutrients experiment
- wants to see if sodium limitation affects the feeding behaviour of ants
- examined the recruitment of ants (attraction towards) to: sucrose (high energy) and salt
- hypothesized ants will be attracted to whichever source based on their need - environmental availability of sodium should affect the diet selection of ants
- made two sets of transects on different distances from salt road, in small intervals in every transect was vial w/cotton filled w/either sucrose or salt
- after some time, collected vials recorded # of ants inside and nearby soil samples to see concentration of salt in ant env.
- results showed soil closer to road had higher salt concentration, ants closer to road mostly chose sucrose and as distance from road increased ants chose more NaCl
- concluded sodium limitation affects the feeding behaviour of ants and how nutrient requirements can affect diet choice
45
define diminishing returns
a decline in instantaneous harvest food as a food patch is depleted
46
what does it mean for a food patch to be depleted
food to be finished in a patch and needing time to be replenished
47
what is the marginal benefit of feeding?
benefit a forager can gain by spending just a but more time in a patch
48
when is the marginal benefit of feeding high? low?
high - forager enters a patch w/abundant food bc the instantaneous harvest rate is high
low - as the patch becomes more depleted - bc of diminishing returns
very low - when patch contains little food - bc it takes a long time to find the next food item
49
define the marginal value theorem
an optimal foraging model that predicts how long an individual should exploit a food patch
50
explain the first part of the patch use by ruddy ducks experiment
- tested predictions of marginal value theorem - as travel time increases, foragers should spend longer in each patch
- build glass aquarium with artificial food patches at bottom (trays of sand containing wheat)
- trained ducks to look through sand to find food - kept trays in fixed location
- released duck and allowed to feed for various different times, collected wheat grains left - tells how much food eaten by duck in specific time
- results of 6 ducks showed that harvest rate did decline as ducks depleted the patch
51
explain the second part of the patch use by ruddy ducks experiment
- placed 2 identical trays at bottom of sand - trained birds to know location and quality of food
- now measured time until first patch sbandoned, travel time btn patches (time to go up breath and come back down)
- collected data on number of grains left in a patch for same six birds
- results showed model accurately predicted patch use of majority of ducks - most were maximizing energy intake rate
52
explain the second part of the patch use by ruddy ducks experiment
- tested prediction that forager should stay longer in a patch as travel time btn patches increases
- increased travel time by changing location of one of the plates
- collected data on how much food remaining
- results showed 5/6 birds ate significantly more food and spent more time at one food patch, as model predicts - ducks were attempting to maximize their energy intake rate, as assumed by marginal value theorem
53
what are some assumptions the optimal patch-use model makes?
- no foraging costs other than travel time
- forager has perfect info about the environment; it knows that all patches are identicak and travel time btn al patches is same
54
what costs did the new patch model include?
includes energetic costs of foraging, predation risk costs, and missed opportunities
55
define energetic costs of foraging
the energy used to exploit a patch and the metabolic costs incurred while feeding
56
define predation risk cost
the fitness cost associated w/being killed by a predator. often equated with the probability of being killed by a predator
- probability of being killed while feeding
57
define missed opportunity costs of foraging
the fitness costs of not engaging in other activities while feeding
58
who developed the new patch-use model?
Joel Brown
59
what does Brown's new model predict?
a forager will maximize its fitness when it remains in a patch until its marginal benefit of staying there (instantaneous harvest rate) declines to equal the marginal (instantaneous) cost of being in the patch
- if two patches have same food and same costs, they should be harvested down to the same food density - stays even if patches differ in initial food density (think assumptions)
60
define quitting harvest rate
the forager's instantaneous harvest rate when it leaves a food patch
61
explain the fruit bat foraging on heterogeneous patches experiment
- tested prediction that food patches will be left w/same GUD if foragers are attempting to maximize energy intake rate (Brown's model prediction)
- made artificial patches that differ in initial resource amount
- trained bats to feed from artificial feeders (cylinders with one opening containing mix of sugar water and protein)
- created diminishing returns by trying rubber band around cylinder so food is harder to get out as less remains
- before experiment, examined harvest rates of bats by letting them eat and recording the total time bat spent at a particular feeder and the amnt of food remaining at the end of night - GUD
- in experiment: placed 3 feeders w/different amounts of food nearby e/o in same environment - creates similar energetic, predation and missed opportunity costs
- had 5 different feeding stations - collected amnt remaining at end of night for few days
- results showed that bats did equalize GUDs as predicted by model - Brown's patch use model can be used to explain feeding behaviour in many organisms
62
define giving up density
the density of food items in a food patch after being exploited by a forager
63
explain a little about Egyptian fruit bats
- large
-nocturnal
- live in tropical Asia and Africa
- obtain juices and pulp from a variety of fruits and also feed on nectar
64
how does Brown's model differ from Charnov's original patch use model?
- can be applied to a wider range of ecological conditions because allows for differences in patch resource amounts and foraging costs
65
why might foragers spend slightly longer in food patches than predicted?
in nature, most animals can only estimate the number and quality of food items in each patch they encounter
66
how do animals estimate the quality of a patch?
individuals gain sample information about a patch from the quantity and quality of food they find
- may also have prior knowledge about frequency of food types (quality) in the environment from previous foraging events
- combining sample information w/prior knowledge
67
68
what is Bayesian estimation?
process of combining sample information and prior knowledge - done mathematically using Bayes' theorem
69
what is a kleptoparasite?
a forager that obtains food from other individuals
70
explain the research on kleptoparasites that steal food from the sea star
- echinoderm extracts large buried clams to eat - long process
- lots of opportunistic carnivores unable to extract rely on it to obtain food
- documented interactions among these species and measured mass of clam before and after kleptoparasites to see how much of it they obtain
- after initiation of eating by sea star, kleptoparasites arrived within some time and began contacting the feeding sea star and successfully obtained food (the clam) - sea star lost some of prey to kleptoparasites
71
define producers
an individual in a group that searches for food
72
fine scrounger
individuals in a group that exploit the food discoveries of others
73
define usurp
take forcefully
74
explain the relationship between scroungers and producers in a group
- need at least one producer
- as proportion of scroungers increases, fewer scrounging opportunities
- foraging success (fitness) of scroungers should be high when they are rare relative to producers in a group
- foraging success of scroungers should decline as frequency of scroungers in a group increases
75
which model developed to answer what frequency of scroungers should be found in a foraging group
producer-scrounger game theory
76
what does the producer-scrounger game theory model assume?
- searching for (and finding) food is incompatible w/searching for scrounging opportunities (true bc finding food head down vs scrounging head up)
- feeding rate (fitness) of scroungers decreases as the frequency of scroungers in the group increases - fitness of scroungers high when scroungers rare but low when scroungers common
77
what does the producer-scrounger game theory model predict?
there is an equilibrium frequency of scroungers and producers at which their fitness is equal: both behavioural strategies can persist in a population at this stable equilibrium
78
explain the spice finch producer-scrounger game experiment
- can behave as both producers and scroungers in captivity
- trained birds to feed from an artificial food patch w/2 sides - one side trained as producers (by pulling string) other side trained as scroungers (everyone who ate)
- created multiple flocks of 6 birds - ranged from 1 producer and 5 scroungers to 6 producers and 0 scroungers
- when patch uncovered, easy for scroungers to get food, when covered, less food for scrounger
- each trial focused on focal individual and its feeding rate
- results found feeding rate for scroungers was lower when patches covered
- for uncovered and covered, feeding rate of scroungers declined as proportion of scroungers increased
- feeding rate of producers unaffected for both patch types
- covered: producers and scroungers equal fitness (when 1 scrounger and 5 producers)
Experiment 2
- kept patch covered for some days and uncovered for some
- individuals could either be scrounger or producer - tested foraging strategy of focal individuals in different flocks
- results showed individuals adopted one or other role and adjusted scrounger frequency to the predicted values: for covered, less scrounger, for uncovered: more scroungers
- conclude: foraging spice finches able to make small adjustments in behaviour based on current environmental condition and behaviour of others
- within stable groups of conspecifics, some find food others usurp, but within the group, producers and scrounger obtain similar feeding rates
LifeSci 2D03
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