Animal behavior exam 2

optimal foraging theory

- deciding what, where, and when to eat

- a collection of mathematical models predicting foraging behavior in animals

- example: foraging in great tits, humans

effects of risk on foraging behavior

- resource variability, predictability, and motivational state

- example: utility functions in yellow-eyed juncos

effects of sociality on foraging behavior

- group size, cooperation and public information

- example: bluegill sunfish, wolves, starlings

unique adaptations in foraging (5)

- caching/hoarding

- farming

- hunting

- planning

- innovation and learning

what two factors do many prey choice models say will affect the decision of prey choice

1. energy value (fitness benefit; B)

2 'handling' time (fitness cost; C); includes search time and pursuit time

define profitability

energy value/handling time

what ratio represents optimal behavior or highest profitability

B/C

what is an important and surprising factor that affects foraging

- encounter rate

- math suggests a critical threshold for encounter rate of most profitable prey item

- if you don't come across a profitable prey item a lot, you should find another food source since it is not common enough

explain the foraging example in the great tits

- gave same amount of small and large prey -> ate equal amount small and large

- next gave more large than small prey -> ate much more large

- next gave same amount small and large prey -> still ate much more large

- next gave more small prey -> still ate much more large

encounter rate is important because it directly influences __________

search time; the more time searching for food, the longer animal isn't eating

what is the optimality approach

• only pursue prey if pursuit time is less than average search time plus average pursuit time (P_i < S_avg + P_avg)

• a cheetah should only chase a gazelle if it would be quicker than and have higher chances than trying to catch something else

specialists

• restricted diet

• often display physiological and/or morphological adaptations

• examples: pandas and bamboo; koalas and eucalyptus

generalists

• broad diet

• allow adaptations to changes in prey availability

• examples: black bear, raccoons, rats

evidence of optimal foraging in humans

Ache people: indigenous tribes in Paraguay

• traditional hunter/gatherer tribe - spent as much as 50% of the day foraging

• vast majority of the diet (99%) was from about 9 vertebrates (of >500 possible prey items)

• the prey items taken match predictions of optimal foraging theory

what aspect other than calories do animals take into account when deciding what to eat

• specific nutrients; i.e. salt

• suggests various adaptive hungers

specific foraging example using the elk

• avoids the energy-rich, salt poor plants and goes for the salt-rich, energy-poor plants

• instead of favoring calories the elk chooses the plants that have more salt due to a dietary need for sodium

what two factors do models assume affect decisions on how long to forage in a certain area

1. rate of food intake in patch (fitness benefit, B)

   1. energy payoff decreases with time

2. travel between patches (fitness cost; C)

   1. includes time searching, risk of predation while moving, etc

profitability ratio for deciding where and when to eat

rate of food intake/travel

optimal behavior → animals demonstrate highest profitability (B/C) and ….

optimal ‘Giving up Time’ (GUT_opt)

this theory generates testable predictions or…

the marginal value theorem (a graphical solution)

longer travel time should result in…

longer time in the patch - more reluctant to leave

• if spacing of patches differ → move travel time only and not net energy gain curve

poorer quality patches should result in…

longer time in patch → other places are not great either

• change net energy gain only and not travel time

experimental test using great tits given choice of ‘patches’

put mealworms under a pile of sawdust in a container with a lid on it in a tree, then made the lids heavier to increase travel time → as travel time increased, time in the patches also increased

risk-sensitive optimal foraging theory

incorporates environmental variances into OFT → reveals importance of motivational state (hunger); foraging behavior based on how hungry the bird is

higher environmental variability =

higher risk

experimental test for the effects of risk using yellow-eyes juncos

• given choices of patches with different variability (risk) in food payoff

• patch 1: fixed number of food items → stable

• patch 2: ½ time no food items, ½ time many food items → higher risk, higher reward

• both patches have the same average reward / # of food items

if the birds were positive energy budget:

• utility/value of food

• risk prediction

• patch choice prediction

lots of food

• value of food remains same/decreases with each item

• risk-averse - prioritize stability and certainty

• patch 1 (low variability)

negative energy budget

• utility/value of food

• risk prediction

• patch choice prediction

food is more scarce

• value of food increases with each item

• risk-prone - embrace uncertainty for potential higher rewards

• patch 2 (high variability)

graph for negative energy budget

graph for positive energy budget

when it comes to group living and foraging, in general when group size increases…

foraging efficiency increases also

increased foraging efficiency when group size increases may not be a result of cooperation. what is an example where efficiency is not due to cooperation?

• the bluegill sunfish

• more individuals → faster at finding prey and more prey flushed from environment

what is an example where efficiency is due to cooperation?

• hunting in chimps and african wild dogs

• in areas with low individual foraging success, cooperation in group foraging evolves → the more animals in the pack, the more food you get

curve shape of individual benefits to living in a group

bell shaped curve

curve shape of individual benefits to solitary living

straight line

what does theory and experimental evidence suggest about there being an optimal group size

it suggests that group size is generally larger than ‘optimal’

• animals often live and forage in groups that are larger than the group size that would provide the greatest benefit to each individual

insider vs outsider

• insider: an animal already living in the group; benefits most when the group is at its optimal size; adding more animals can increase competition for food and decrease individual benefits

• outsider: an animal currently living alone that wants to join the group; even if the group is already past its optimal size, joining may still provide more benefits than living alone

an additional benefit of group foraging is access to…

public information

how can individuals use foraging success of others to help their own foraging success

helps them learn about patch quality, variability, and travel time

access to public information results in…

‘information centers’

experimental test in starlings - public information

• given patches with no seeds or few seeds

• tested alone (B1) or with a partner (B2)

• partner (B2) could sample few or all cups

• measured for time to leave empty patch

• results showed that you give up faster with a partner that sampled all cups because you gain public info

what animals do caching/hoarding (food storage)

• corvids (crows, jays and relatives)

• parids (chickadees, tits and relatives)

• rodents (mice, gerbils and relatives)

• carnivores (felines, canines and relatives)

there is a correlation between _____ and _____ in relation to caching/hoarding

memory and caching ability

how was caching tested experimentally

• chickadees

• birds collected from different latitudes and altitudes; tested for caching ability

• northern birds cached more often, had better memory, and larger hippocampus

what animals do ‘farming’

• leaf cutter ants - fungus

• damselfish - algae

• farmer ants - aphids

explain the farmer ant and aphid symbiotic mutualistic relationship

the ant protects the aphids from predators and then the aphids secrete “milk” for the ants to eat → the act of the ants’ antennas touching the aphids makes them secrete the milk

hunting techniques that are unique adaptations in foraging behavior

• pursuit (chase)

• stalk

• ambush (sit and wait)

• group/pack hunting

• scavenging

to demonstrate planning, ethologists must demonstrate what two things

• behavior is novel or learned (not innate action like migration)

• behavior is tied to future, not current, motivational state

what animals are a good model system to study this and why

scrub jays - show remarkable episodic memory, not only remember where they cache food, but remember if they were watched and who was watching

scrub jays experiment

• exposed to alternating compartments every other day

  • crushed pine nuts (can’t be cached)

  • no food

• given whole pine nuts to cache and access to both compartments with caching board

• result: cached more pine nuts in ‘no food’ compartment

scrub jays follow up experiment

• exposed to alternating compartments

  • peanuts

  • dog food

• given both foods to cache and access to both compartments

• cached dog food in peanut compartment and vice versa

• suggests they prefer a varied diet

innovation and social learning is important for animals who…

encounter a wide variety of new food items

• scavengers (rats, mice, pigeons)

experiment using pigeons for innovation and social learning

• required pigeons to pierce red paper to access food in a box

• control; no model → no learning

• local enhancement; observed model eating from box → learn - took some time

• blind imitation; observed model pierce red paper, but not eat → no learning

• observational learning; observed model pierce red paper, and eat → learn - quicker

second experiment using pigeons and innovation/social learning

• required pigeons to remove rubber stoppers from test tubes to access food

• pigeons exposed to row of test tubes with stoppers

• some test tubes contained food (which birds couldn’t see)

• when birds opened tube with food, seed spread for others to feed

results of second experiment

• only 2/16 birds learned to remove stoppers (producers)

• other birds followed producers and ate when food was present (scroungers)

• when producers were removed, scroungers couldn’t solve task

what questions does the second pigeon experiment raise

• are scroungers or producers fixed phenotypes - lack of phenotypic plasticity

• why so many more scroungers than producers

• does scrounging inhibit social learning? or does poor social learning lead to scrounging behavior

follow up experiment to the second pigeon experiment

• same task with a single demonstrator paired with a single observer

• all individuals were able to learn task - when they didn’t automatically receive food

• however, if food was released to observer when demonstrator opened the tube, observers didn’t learn

  • if they get the food, why would they need to learn

define coevolution

reciprocal influence of two interacting species on each other

mutualistic vs antagonistic (coevolution)

• mutualistic: both benefit (plants/pollinators)

• antagonistic: one benefits at the cost of the other (predator/prey)

life/dinner principle

unsuccessful predator goes hungry; unsuccessful prey doesn’t go anywhere

predators can switch _____, prey can’t switch _____

prey; predators

generation time of ____ < generation time of _____

prey; predators

3 lines of defense

1. avoid detection

2. avoid capture

3. fight back

three types of camouflage

1. crypsis: blending in with the environment

2. mimicry: presence of similar appearances and behavior between multiple species

3. aposematism: highly obvious signal of unpalatable organism

examples of animals that do morphological crypsis

• pepper moths

  • natural selection changed moths to black while tree was covered in ash, then back to white after some time when the tree turned back to original color

• pocket mice

• mantids

example of an animal that does behavioral crypsis

gulf toadfish

• toadfish go quiet when dolphins are hunting and pops are heard

batesian mimicry

harmless organism mimics harmful one

• king and coral snake

• moray eel and spotted plesiops: plesiops tail looks like the head of an eel

• parrot snake and hawkmoth larva

• zebra spider and snowberry fly

Müllerian mimicry

two (or more) harmful species mimic each other

• monarch and viceroy butterflies

• Heliconius butterflies

• yellow jacket and cuckoo bee

aposematism

highly obvious signal of unpalatable organism

• poison dart frog

• coral snake

• nudibranchs

• polychaetes

effects/benefits for living in a group

• dilution effect

• confusion effect

• vigilance effect

dilution effect

the reduction in an individual’s risk of predation as group size increases, because the predator’s attention is spread over more individuals

• sea turtles hatching on shore and all moving towards the ocean

confusion effect

hard to pick out a single prey item due to colors, patterns, outlines

• example: zebras

vigilance

the more eyes (prey), the less close predators can get

pigeon flocks and goshawks (avoid detection)

hawks had a higher success attack rate when the group of pigeons was smaller

fleeing

• a second line of defense - avoiding capture

• asian carp jumping out of water; early hatching in tree frog embryos due to snake attack

three main factors that affect if and when to flee (flight initiation)

1. distance to refuge

2. predatory effects: pred speed, size, type, starting distance, pred intent, number

3. prey experience: predator density, sequential approaches

approach behavior

• Thompson gazelles and cheetahs

• gazelles approach cheetahs

• allows the gazelle to gather info on the cheetah

• also removes element of surprise: cheetah knows it has been spotted, so harder to sneak up on gazelle

signaling/alarm calls (avoid capture)

• stotting in gazelles

• tail-flagging in deer: warns other deer that a predator is nearby

• alarm calls in prairie dogs

deception (avoid capture)

• thanatosis (feigning death) in bean beetles

• heritable trait: some are good at playing dead, some are not - if better at playing dead then not as good at getting away

physical defenses (fight back)

• armadillo: hard outer shell

• porcupine: sharp quilles

• polychaetes (bristle worms): pointy little hairs

chemical defenses (fight back)

• skunks noxious spray

• poison dart frog’s toxins

• annelid bioluminescent ‘bombs’: sacs break off from the body and glow and the animals can get away

• bombardier beetle’s acidic spray: boiling acid; 2 chemical secretions mix together

group defenses (fight back)

• muskoxen ‘circle of horns’

• ground squirrel and otter mobbing behavior

simple definition of communication

transfer of info from a signaler to a receiver

more complete definition of communication

process in which a sender uses a specially evolved signal to modify the behavior of the receiver

• ‘specially evolved signal’ implies fitness benefit to signaler

  • also differentiates between signals (shaped by natural selection) and cues (incidental by-product)

what 3 things does the study of animal communication require

1. observation and description of signal

2. analysis of info conveyed/transferred

3. analysis of mechanism(s) and selection pressures on signal

different types of communication modalities

• chemical

• acoustic

• visual

• tactile

chemical modality

requires chemical signal from sender and specific olfactory receptor in receiver; most ancient form of communication

• examples: pheromones, cuticular hydrocarbons, territorial scent markings

acoustic modality

requires generation of vibrational signal in sender and mechanoreceptor(s) in receiver; can travel long distances

• examples: whale song, cricket chirps, gorilla chest drumming

visual modality

requires movement of body or body parts to reveal specific patterns and/or colors

• examples: birds-of-paradise displays; stotting; bioluminescence

tactile modality

requires direct contact between signaler and receiver

why would 3 nocturnal insects use 3 different communication modalities as their primary means to attract mates (moths, crickets, and fireflies)

Moths

• active flier, can easily travel to locate mates

• high predation risk from bats

• use least detectable signal (chemical)

Crickets

• ground dwellers living in tall grass; more difficult to locate mates

• use signal that travels around barriers and long distances (acoustic)

Fireflies

• active flier

• chemically toxic and distatseful

• light producing organ evolved in larvae as aposematism signal to predators

• use fast, energetically low-cost signal (visual)

direct vs indirect signaling

face-to-face confrontation vs scent mark

immediate vs gradual signaling

• firefly courtship elicits immediate response from partner

• ring dove courtship elicits physiological/behavioral cascade

discrete vs graded signals

all or nothing (fireflies) or varying intensity (honeybees)

signals as language

• combining two or more signals to indicate new meaning

• context dependent signals

benefits of group foraging ______ with communication

increase

example of how communication helps group foraging

honeybees will share food location via ‘dances’ → the type of dance indicates distance (round<sickle<waggle)

another group activity where the benefits increase with communication

defense

example of how benefits of group defense increase with communication

selfish alarm calls in ground squirrels

• sex and age bias in sounding alarms

• can learn to ignore calls of unreliable individuals

graph showed that adult females are much more likely to give alarm calls than others

learned alarm calls in meerkats example

adults show stronger behavioral response to alarm calls than pups