Transcript Bystander effects

Bystander effects
• Ok, lots of support for winner and loser effects
• How about bystanders?
• What affect does seeing another win or lose
have on YOUR chances of winning or losing?
• What does watching give you?
Swordtail fish
• If you see an aggressive encounter, you can
learn valuable information for the future.
• Test for these effects with control where
bystander could not see outcome of combat
• Treatment where bystander could see but
combatants couldn’t
What happens when you now pit bystander
against winner or loser?
Outcomes
• Where bystander could see outcome, tended
to avoid contest with winner more than
bystander that could not see contest.
• AND not escalate
as often,
Outcomes
• Bystanders that saw outcomes and those that
did not, treated losers about the same way.
• But length of aggressive encounter made a
difference.
• Initiated more against
losers that left contest
quickly.
What does this mean?
• Bystander can use information to its
advantage.
• Judges fighting skills of both combatants
based on not only on who wins or loses but
how escalated the fight becomes.
• Future aggressive actions then affected by this
information.
Audience Effects
• Here we are looking at how onlookers affect
the outcome of the conflict.
• Chimpanzees: Aggressor screams and victim
screams.
• In mild encounters, victims don’t scream any
longer with or without audience
• In severe encounters, victims scream longer
and louder with an audience.
Outcome
• Who is in the audience makes a difference!
• If there was an equal or higher ranking
individual to the
aggressor, was
present.
Why?
intervenes and
breaks up fight.
Summary
• In this case combatants seem aware of who is
in the audience and adjust their behavior
accordingly.
• Area rich in research possibilities to see not
just how they may adjust behavior but how
audience might alter outcome.
• Would you fight harder depending on who is
watching??
Aggression summary
• Aggression behavior is over resources
• Is linked with testosterone and various other
hormones.
• Can be modeled with game theory where
outcome depends on value of the resource and
the costs associated with trying to get that
resource.
• Outcomes often decided on physical advantage
but also depends on how each combatant values
the resource.
Aggression summary
• Can result in an “ordering” of society but not a
peaceful one.
“Pure behavior”
• Before we move on to behavioral ecology, a
few other behavioral categories to cover.
• First of these is disease and animal behavior.
(Chap 16).
• As we will see with other “threats” to health
and life, many animals have developed
behaviors aimed at reducing their chances of
catching diseases.
• Here we will look at a few of them.
Avoidance of disease
• Avoidance of habitats
-Tree frogs: were able to determine presence of
snails (intermediate host of trematode
parasite) and avoid laying eggs in these ponds.
Avoidance of individuals
• Bullfrogs: In tadpole stage, evidence that
uninfected individuals preferred to associate
with other uninfected ones, avoided inflected
individuals.
• How did they tell?
• Seems chemical cues were used.
• Others? Often see avoidance of “unhealthy”
individuals. Part of the sexual test is a health
check!
Self - medication
• Seems we are not the only ones who like to
self medicate!
• Two broad categories
• 1) Preventative
• 2) Therapeutic
Preventative medicine
• Many species use potentially anti-bacterial
plant substances in their nests.
- Starlings add fresh herbs – led to higher body
weight of fledglings.
- Many primate species eat clay, dirt, and rocks
to reduce indigestion, as an antidiarrheal
agent, absorb dangerous plant compounds
Preventive medicine
• “Anting” by birds and mammals: rubbing
crushed ants on feathers and fur. Formic acid
aids against tick infections
• “Fur rubbing”: many primates rub fruits,
leaves, and vines on their fur, which have
antimicrobial effects.
Therapeutic self-medication
• Use of leaves by Chimpanzees against
tapeworms.
• Other primate
do the same.
- Dogs and cats
eating grass.
Summary
• Growing evidence that many species self
medicate,
• Obvious evolutionary advantage to individuals
who “discover” the use of these medicines.
• Often with similar substances we commonly
use today. In fact, starting to try and identify
others that are being used that we might be
able to use!
Next: Personalities!
• Used to consider people who thought animals
had “personalities” were them selves
“personalities”!!!
• But more and more research is demonstrating
that indeed there are individual differences in
behaviors or personalities.
• Not surprising in that we have been talking
about natural variation in most behaviors.
How do personalities differ?
• One common way is Boldness vs Shyness
• Boldness: tendency to take risk in familiar and
unfamiliar situations
• Shyness: reluctance to take such risks or
reluctance to engage in unfamiliar activities at
all.
Why would we find both?
• IF we think of evolution as the survival of the
fittest, often hard to see why we would have a
range of any trait.
• IF we consider survival of the adequate, then
in some cases being shy has advantages and
some cases being bold.
Evidence for boldness and shyness
• Do we really find these personality
differences?
• Pumpkinseed sunfish:
• Trapped vs seined
• Trapped bolder
willing to investigate
Were they?
• Trapped adjusted more quickly
Guppies
•
•
•
•
•
Boldness and predator inspection:
Found there were consistent differences
Always bold
Always shy
Bold are colorful
Why be bold?
• It seems to impress the females!
Is she really??
• Will mate with bold males regardless of color
Other than boldness and shyness?
•
•
•
•
•
•
•
What other traits vary regarding personalities?
Gosling (1998) found five aggregate traits in Hyenas:
1) assertiveness
2) excitability
3) Human-directed agreeableness
4) sociability
5) curiosity
Octopus??
•
•
•
•
Turns out they have personalities!
1) Active vs inactive
2) anxious vs calm
3) bold vs inhibited.
Ruffs
•
•
•
•
•
Personalities related to physical differences.
“independent” males vs “Satellite” males
Dark and larger vs light and smaller
Independent set up territories.
Satellites needed to
attract females.
Last: Coping styles
• Related to bold and shy but relative to how
they respond to stress in the environment.
• Proactive vs reactive
• Proactive: likely to remove negative stimuli
from their environment
• Reactive; more likely to hide from new
negative stimuli
Lab rats
• Can breed for proactive vs reactive
• Proactive more likely to show aggression
toward intruder, reactive will hide
• Proactive rats will try to remove or neutralize
a negative stimulus, reactive ones will just
avoid the area where the stimulus is.
Summary
• Good evidence that personality differences
exist: boldness/shyness most studied
Fear
• Recognize it in humans
• TV, Movies, Books, etc. play upon our fears!
• We love to be scared!!
• But what about other animals?
• Often reluctant to recognize it: too
anthropocentric!
Fear
• Talked about aggression
as a behavior
• Widely accepted as a
behavior of animals, no
anthropocentric
overtones.
But why does aggressive behavior
work?
• Needs reciprocal reaction or behavior!
• Call it submissive behavior
• But it is FEAR!
Intraspecific conflicts
• Why does one win and another lose?
• What makes the one back
down?
…..Fear
If not….
fight to
the death!
Imagine if someone was trying to
kill you!
• Would we call it submissive behavior?
What is it?
• No other way to describe it except… Fear!
One of the most prevalent
behaviors
• Considering what we have talked about
regarding aggression and what we will talk
about regarding predation…
• Fear is probably THE one most likely behavior
an organism will experience!
• Also, as you will see, is probably the most
influential behavioral force in ecology
So fear exists
• Many felt it was too anthropocentric to
ascribe fear to animals:
• Talked about “escape” and “avoidance
behaviors”
• But these are the behaviors that are produced
by fear.
Today?
•
•
•
•
•
More acceptable to talk about fear in animals
Still not mainstream
No mention of it in most behavioral texts.
Yet whole chapters devoted to aggression!
So lets look at fear as a behavior
Definitions
• Two important concepts regarding fear (from
psychology)
• 1) motivation
• 2) personality
Motivation
• Fear and anxiety: emotional states that are
induced by the perception of any actual
danger (fear state) or potential danger
(anxiety state) and which are characterized as
a feeling of insecurity
Personality
• Fearfulness: personality or temperament trait
defining the general susceptibility of an
individual to react to potentially threatening
situations. (Just how fearful or anxious you
will be)
Five basic questions
•
•
•
•
•
Survival function “What good is it”
Immediate stimuli “what causes it”
Development “How does it develop”
Phylogeny “How does it change”
Ecological function “How does it affect others”
Evolutionary advantage?
• Fear definitely has survival value to wild
animals!
• Most important threats of injury and death
individual encounters are from predators and
competing/attacking conspecifics.
• Defensive reactions increase the chances of
survival.
• If you don’t fear your predators, your dead!!
What causes fear response?
• Classic is there is a stimulus associated with
behavior
• What is nature of frightening stimuli?
• Gray in 1979 classified fear-producing stimuli
into 5 subdividsion
Subdivisions of fear stimuli
•
•
•
•
•
1) dangers related to evolutionary history
2) dangers related to novelty
3) stimuli you learn are related to danger
4) Intensity of the stimuli
5) stimuli arising from interactions with
conspecifics.
1. Evolutionary history
• “Innate” fear responses
• Usually specific stimuli that are related to
ecology of species, many cross species
boundaries
• Physical dangers: fear of heights, fear of
darkness, fear of dead things.
• Fear of predators: silhouettes of hawks illicit
responses in nestlings
2. Novelty
• Apart from established innate fear stimuli
• Exposing animals to a novel object has been
found to be most potent stimulus leading to
negative emotional response.
• Behavioral reaction similar to that induced by
negative stimuli such as electric footshocks!
• Animals are inherently afraid of NEW things!
3. Learning
• Obvious learning would be a part of
developing the fear process
• Identifies new sources of danger (if you live to
tell about it!).
• Yellowstone elk and wolves
• Identifies new SITUATIONS of danger,
important in ecological aspects of fear.
4. Physical characteristics of stimuli
• Intensity, movement, duration, proximity, etc.
• All can become associated with fear response
• A flying hawk will illicit a response while a
perched one will not.
• Distance the predator is: prey know “safety
range”, e.g. animals in Serengeti
• Behavior of predator: prey can detect if
predator is serious.
5. Interactions with conspecifics
• Can be combinations of previous
• Here conspecific is the “predator”
• Novelty: new animal may provoke fighting
response.
• Learning what are the dangers from others
• Lack of social contact: afraid to be alone!
Ok your scared!
• What do you do now?
• Adaptive response to danger: two
complementary pathways.
• 1) Neuroendocrin adjustments to maintain
homeostasis.
• 2) psychobehavioral changes to neutralize
effect of stimulus
First the neuroendocrine aspects
• Pure neurological responses obvious: Fight or
flight reactions are direct responses of
muscles to nervous responses.
• However, what produces this nervous
response is at the root of how danger leads to
fear leads to the response.
• As we saw earlier, interaction between neural
and endocrine systems plays a big role in
many behaviors.
What is going on when you get
scared?
• Needless to say complex and would be more
appropriate for course in neuroendocrenology
• Object here is to indicate major players and
some insight as to what they do.
• Two major complexes known to be sensitive to
“environmental challenges”
Anatomy of fear
• Sympathetic Adrenal Medullar system
• Hypothalamo-Pituitary-Adrenal Axis
• These are the structures/areas of nervous
system.
• What do they do?
What happens when you get
scared?
• Back in 1935, noted that emotional reactions
such as fear and rage threaten the integrity
(homeostasis) of the body
• In response, body attempts to maintain
internal environment.
• In BRIEF, Fear stimulus causes release of
adrenal medullary catecholamines and the
ACTH (Adrenocorticotrophic hormone) to
Glucocorticoids route we saw earlier
Familiar ground
• Saw earlier that these secretions help
organism to react behaviorally rapidly.
• Inhibit glucose uptake and fatty acid storage
• Stimulate release of glucose, amino acids,
fatty acids
• Shunt blood flow from nonessential body
areas.
• All aimed at enabling muscles to react rapidly
Response is graduated!
• Fine and good but fear response is not an “all
or nothing” reaction.
• What factors control the extent of the
response to fear?
• Why are we more scared sometimes??
• How do we control our fear??
Counter balances to fear response
• Sex hormones affect reactions: females
respond less to challenges than males
• BUT testosterone injected into female cattle
reduces fear reactions.
• Prolactin secretions increase with exposure to
challenges and may lower reactivity to
challenges.
More?
• Endogenous opioids (endorphins) reduce
intensity of response to challenges.
• So not all or nothing but animal does seem to
have some control over how much it will
react.
• What are factors that help animal modulate
this reaction?
Adjusting fear response
• Prior experience: rats place in area where
they received shock before, while have greater
fear reaction than naïve rats. (likely works
other way too)
• Controllability: Degree of control animal can
exert over situation will affect degree of
response. Perceives danger is under its
control, reduces intensity of response
Controllability
• Examples: Availability of familiar
environments will lower fear response to
novel environment.
• Chewing on nonedible objects seems to help
in mice. (fingernails!!??)
• Being able to move in general helps to reduce
fear reaction.
Adjusting fear response
• Predictability: ability to predict when
challenge will occur helps reduce reaction
• Repeated exposure to novel objects becomes
reduced IF it is done on a regular basis
Result is biological response to a challenge is not
stereotypic but influenced by psychological
factors and behavioral strategies
More?
• Negative feedback in the neuroendocrine
system:
• Glucocorticoids exert negative effect on own
secretions and other fear-activated neural
circuits.
• So system itself has built in safeguards to
excess reactions!
• And can aid animal in controlling fear reaction,
depending on its ability to cope with it, as
above.
here
End effect?
• Fear-producing stimuli and fear-related
responses function interactively.
• Result of:
• 1) properties of threatening event
• 2) possibility of controlling the danger
• 3) neuroendocrine state of the individual
Variations in Fearfulness
• Have seen that individual can vary its response
• Question is does Fearfulness vary across
individuals?
• personality or temperament trait defining the
general susceptibility of an individual to react
to potentially threatening situations.
• Are some more prone to be scared than
others?
Some do scare easier than others!
• Not surprisingly the answer is yes!
• Variation in test results support this variation
in response to fear.
• In fact, have been able to select for strains of
mice and rats based on their reactivity to fear
stimuli
• Basically selecting for the control of the
neuroendocrine responses.
How do we measure fear?
• Difficult to measure the emotional state of
fear itself.
• Things we have talked about, psychobiological
reactions to fear stimuli are only indicators.
• But, give that, how do we measure them?
• Forkman et al. 2007 provides a review of
various tests used, primarily on domestic
animals.
I am sure you all read it!!
• Don’t want to go into detail on any one
method.
• Just provide an overview of how we can go
about testing for fear responses.
• 1) Novel arena/object tests: area where
subject enters and behavior noted or its
reaction to the appearance of a novel object.
• Also called open-field test
• 2) handling tests: Human
interactions/handling. Record reaction of
animal to various forms of handling from soft
to hard.
• 3) Restraint tests/tonic immobility: used in
birds, simulate predator and bird goes
immobile or “feigns” death. Length of time it
does so is used as a gauge of fear.
More?
• Various others, often modifications of
previous ones.
• How good are they?
• Each has strengths/weaknesses
• One recent one that is used with wild animals
is the level of vigilance.
• Usually related to predation risk.
Summary
• Fear exists: strong evolutionary force
• Complementary behavior to aggression
• Produces many of the outward behaviors we
see: submission,
• Neuroendocrine basis
• Interactive with the extent and property of the
fear stimulus
• Is measurable on a variety of levels
Summary
• Is one of the most prevalent groups of
behaviors
• Is important factor in many of the organismenvironment interactions….or
• BEHAVIORAL ECOLOGY.
• Will run into it again….
here
Behavioral ecology
• What is it?
• Obvious: blending of behavioral and ecological
theory
• Why?
• Only in the laboratory do animals “behave” in
a vacuum: environment is the medium.
• Most behaviors occur in real-life situations
• Behaviors often have feedbacks on ecological
processes.
Behavioral ecology
• So, behavior and ecology cannot be separated.
• Eluded to behavioral ecology every time we
talked about how individuals interacted with
environment, e.g. nesting habitat and
parenting behavior, or with other species, e.g.
predator-prey
• Now need to address it fully
• In many cases, will be looking at behaviors we
are now familiar with but in relation to
ecology
Lets begin!
• Where do we begin??
• Basics: behaviors aimed at keeping your
energy machine alive!
• First of these is getting the energy you need:
Foraging (Chap 10)
Foraging behavior
•
•
•
•
•
•
Obvious important set of behaviors!
If you don’t eat, you die!
But…what do you eat?
…and why?
Where do you look for it?
Just a few questions concerning foraging
behavior.
• Answers to these shape behaviors we see
What do you eat?
• Actually two basic questions.
• One is deciding what food to eat.
• The other is determining what a specific food
type looks like.
• Lets look at distinguishing among possible
foods first
Search image theory
• One suggested hypothesis on how animals
distinguish among food types:
• Animal encounters food type repeatedly, they
form a representation (image) of that food
type.
• Representation becomes more detailed with
experience.
• Animal gets better at finding this food type
What are they keying in on?
• Some debate:
• Some say: keying in on one or two attributes
of the food (color, pattern, movement)
• Others say: more total image of entire food
item.
• In both cases: learning something relevant
(stimulus-response) and helps to be more
efficient in finding more.
What do they eat?
• Ok, they can develop skill in identifying
specific food types but which one(s) should
they choose and why?
• Lots of descriptive studies
• In 1960’s developed theory as to making food
choices:
• Initially based on the concept of optimization
Optimization
• Idea was that there should be selection
pressure for organisms to optimize their
energy gain from their foraging efforts.
• Basically the ratio between energy gains and
costs.
• Those who did so, ate more, raised more
young, etc. …were the fittest.
• From this logic came Optimal foraging theory
Initial works
•
•
•
•
•
1966: McArthur and Pianka/ Emlen.
Proposed energetics important and costs.
Idea of ranking foods
Idea of optimization in food choice
Basics: as food becomes abundant, you
specialize
• There will be a limit to the number of food
types used: cost/benefit of adding new items
Arguments against optimizing
• Optimizing means eventually leading to the
BEST way of doing it.
• Kind of like Evolution’s “survival of the fittest”
• Should lead to one “optimal” form.
• Better is: survival of adequate
• And: Adaptive foraging theory.
• Semantics? Reflects individual’s constant
adjustment to changing conditions.
Optimal (adaptive) foraging theory
• A theory based on looking at animal decisions
(the decision making process then is the initial
behavior, the need for food is the stimulus
driving the behavior)
• What decisions?
• Besides deciding what to eat, OFT also
attempts to explain other foraging decisions.
Basic foraging decisions
• When foraging, animals have to often make
decisions:
• What to eat (Which is the best)
• Where to eat (food not uniformly distributed)
• How long to forage in a certain area
• Where do you go next?
What to eat?
• Two levels: what is food providing
• Which food provides it better?
Foraging rules: what should we
select for?
• Diet selection: what factors to take into
consideration?
• Caloric value: obviously, this is the principle
gain.
• More calories the better!
• Will see later, also other nutrition
considerations, not just all Kcals.
Costs?
• Counter that with costs: how much does it
cost you to get that energy?
• May not be as simple as maximum Kcals
• Ease of handling: Pecans vs hickory nuts vs
acorns; deer vs cow,
• Risk: of being killed… of being injured.
• Ease of finding: the best may not be the
easiest to find! (search times)
Search times
• Because looking for a food source costs you,
must decide from different “quality” sources
(kcal basis) based on relative abundance of
each.
• Major area of investigation in food choice part
of foraging theory.
• A high energy but low abundance food may
actually be less efficient than a lower energy
but more abundant one.
But how do you decide?
• The main problem here is when to decide to
switch from one food source to another, based
on their respective cost/benefit ratios when
the benefits are fixed but costs can change.
• When is it cost efficient to switch?
Initial models
• Rules: Forager can’t search for/handle more
than one item at a time.
• Fixed number of foraging hours (the clock is
ticking)
• Each food item has its own unique set of
inherent benefits (currency: kcal) and costs
(handling times)
• Search time is a cost and is variable depending
on abundance, prey encountered sequentially
Ranking food items
• The third rule allows a ranking of food items
from highest to lowest: A >B>C> D etc. on
their “inherent” value. This is idea of
McArthur and Pianka
• Now need to see what happens when their
“relative value” changes with search times.
Results
•
•
•
•
Mathematical treatment
Results in a Type II feeding response
Forager can only eat so much!
But more important regarding food type 2
Diet rules
• Basically, should broaden diet when principle
prey 1 drops below a certain level.
• Considered “optimal” strategy.
General predictions
• Should rank food types relative to profitability
• Should always include most profitable prey
and only expand to less profitable when 1st
does not meet needs
• Thus decision to switch is based on
abundance of most profitable not less
profitable
• All or none response: either always accept or
never accept them.
Does it hold?
• Great tits: offered differing proportions of high
value (large food item) and lower value (small
food item).
• Bluegill sunfish: offered three different prey
items.
Results: great tits
here
Results: bluegills
Do they hold?
• Works the best for herbivores or predators of
sessile prey
• Not so well with predators and mobile prey
• Also not so well under predation risk.
• Does not include other needs e.g. minerals,
proteins, etc. Not just all Kcal!
Other dietary requirements
• Not just all Kcals
• Water intake: animal may alter diet from
“ideal” to eat a lower Kcal but higher water
content food.
• Trace minerals: Zinc, etc., animals will again,
purposely consume less than ideal to satisfy
need.
Salt
•
•
•
•
One big one for many herbivores is salt.
Need Sodium for body functions
Many terrestrial plants low in sodium
Some species, like the moose, will supplement
with low Kcal but high salt, aquatic plants.
• Some will travel extensively to salt licks,
forgoing foraging opportunities.
Predators?
• Perfect food: body constituents similar to
themselves! >90% water!
• Handling time becomes most important
• What is involved?
• Size: return on investment, too small to deal
with.
• Size: chance of injury becomes important.
Predators?
• WHERE you forage becomes important
• Habitat mediates risk and success of foraging
in predators, will look at more later
• Illustrates next question regarding foraging:
• Where do I eat?
Patch selection
• First we have to remember that the
distribution of food resources is not uniform
• Habitat heterogeneity is pretty much
accepted.
• So we can talk about habitat or food patches
on a landscape scale.
Patch characteristics
Size
Shape
Juxtaposition
Configuration
Patch quality
• All these add to patch quality: ratio between
benefits and cost
• Benefits: kcals
• Costs: getting to patch, foraging within patch
• So one of the major decisions regarding where
to forage is whether patch provides what is
needed at a favorable ratio.
Landscape of opportunity
• So, regarding the question of where to eat, we
can envision the landscape as offering varying
choices, each with their unique ratio of costs
and benefits.
• So through the eyes of the forager, we
envision a landscape of opportunities.
• Forager makes decisions on where to go.
Now your there, eating happily
but..
• How long do you stay???
• Fixed food level: more you eat, less there is
left!
• Do you stay until you have eaten it all?
• Or do you leave sometime before then &
when?
• What is the best strategy?
Cost/benefits
• Benefit of staying: known food source
• Cost of staying: diminishing returns/ may be
better patch out there.
• Benefit of leaving: finding patch with higher
resource value
• Costs: travel costs, may find patch of lower
quality!
• What to do, what to do???
Are there leaving rules? (exit
strategy)
• Charnov (1976) proposed the marginal value
theorem as a possible leaving strategy
• What is it based on?
• Again, variation in patch quality over
landscape
Patches of different qualities
#’s = food intake rates, e.g. # 2 means can find and consume 2 items/time
Average = 3
1
2
5
1
4
2
3
3
Enters patch with quality 4: how long should it stay?
Marginal value theorem
• Should stay until marginal value rate of food
intake, equal to average food intake across all
patches.
• Enters patch with #4 rate but as consumes,
rate drops: 3.8,3.6,…etc.
• Eventually reaches 3.0
• Then it should leave:
Why??
• On average, if searches randomly, has a good
chance of finding higher value patch.
• Confounding factors:
• Travel costs: higher the travel costs, longer
should stay (again cost benefit ratio)
• Leads to last question
Where do I go?
• The last of the 4 questions: when I do leave,
where do I go next?
• Obviously requires some knowledge of
foraging landscape: basic premise in behavior!
• Given that animal has some information on
resource levels (time since visit, etc.), which
patch should it select?
Travel time
• Obvious: should avoid below average patches
• Biggest determining factor is travel time
RELATIVE to patch quality.
• IF all possibilities above average but different,
then net gain depends on costs of getting
there!
• Should be willing to travel further for a higher
quality patch/visit lower quality one if it is
close.
Other factors?
• Variance of food quality and where to go
next?
• Example: two types, one consistently has a
given level of food.
• Other ½ the time may have none or may have
twice as much! This is not known at the time.
• Which do you choose?
• On average, value is the same.
Risk sensitive foraging
• Risk in the sense your betting (taking a risk)
that if you go to the variable source, it will
have food. If not, you loose!
• What should you do?
• What would YOU do?
Depends on your hunger state!
• Three possibilities: three outcomes
• 1) each item of equal value: In this case, really
no concern if you lose or not, if you lose, you
move on.
• So, should show no preference for either
patch
2 ) What if your satiated?
• Each has value but each additional one has
less. So no advantage to take the chance for a
higher reward and should actually prefer the
lower but constant food patch.
• Referred to as Risk-averse: not willing to take
the risk on an uncertain food source.
3) If your starving?
• Here each additional food item has increasing
value: one more further from starvation.
• What to do?
• Should select the variable food source!
• Why?
Risk-prone foraging
• Should take the most variable because:
• Known consistent food source may not be
enough, you know it is there but is just not
enough.
• IF you win, payback is sufficient to “pull you
from the brink” of starvation.
Evidence?
• First tested in juncos (Caraco et al. 1980) and
found to apply.
• Hungry birds more likely to choose tray with
variable but higher # of seeds.
• Since found in variety of species birds,
mammals, invertebrates
here
Group size and foraging behavior
• Ok, Optimization or at least adaptive
strategies seem to be taken into consideration
• Apart from the four questions, what other
considerations are there?
• First is group foraging
• Again, would seem counter productive, having
to share!
When to forage in groups
• However, many species do it.
• IF we assume foraging is honed by natural
selection, the truism is that in these cases,
benefits must outweigh costs!
• But how?
• Need to look at factors regarding group
foraging to understand better.
Role of group size?
• Basically, increasing the foraging group
increases amount of food each forage
receives, to a point!
• Bluegills:
Why?
• More eyes/more efficient capture.
Public information
• Another advantage to group foraging is the
sharing of public information
• Basically: gather information about food
resources from actions of others in the group.
• Sources of food/quality of food patch, etc.
Predictions
• If this information is being transferred, predict
that social foraging individuals should leave
poor patches sooner than solitary foragers
• Basically use success of co-foragers to make
decisions
• Support: Individual without
or with co-feeders
Left poor feeder faster when
with others.
More
• If naïve bird paired with one that had total
information on cups, left the fastest.
• Evidence that 1) information was transmitted
• 2) influenced foraging decisions.
Caching behavior
• One thing, find food patch, eat and leave
• Another thing, find food patch, eat, store
“excess”
• Reason for behavior:
• Pulsed resources: type that can be stored
• Harsher, less productive environments.
Food abundance
• Chickadees
• Less food
more
caching.
- More caching
less search
time.
Common behavior
• Squirrels, we know
about
• Many bird species do
it
• Acorn Woodpecker
•
•
•
•
Caching behavior is two behaviors:
Idea of “planning ahead” –for the future
Second is remembering where you put it!!
Remembering seems related to volume of
Hippocampal region of the brain: spatial
memory.
Evidence
• Data from 6 species of birds
Planning for the future
• The big question: do animals plan for the
future?
• When they cache food, is this considered
planning for the future?
Criteria for planning
• Two requirements recognized to demonstrate
planning for the future
• 1) Must be a novel behavior, not a
manifestation of innate action, such as
migratory behavior
• 2) must NOT be tied to current motivational
state of animal but to an anticipated one in
the future
Test for planning
• Western Scrub Jay
• Caches
• Has great memory: specific events, where the
cache food and who might have watched
them do it!
• Do they plan for the future?
The Test!
• Over 6 days exposed to one of two
compartments: one contained ground-up pine
nuts and the other nothing.
• Fasted night before test
• Test was exposure to area with the
compartments but now area had bowl of
whole pine nuts (cacheable items).
• Cache sites added to each compartment
• What did they do?
The results
• Jays cached more nuts in compartment that
had been consistently empty before.
• Suggested they were planning ahead for when
those compartments would be empty as
before.
• So evidence that caching behavior does
involve planning ahead.
Return to foraging strategies
•
•
•
•
•
•
The four basic questions:
What to eat
Where to eat
How long to eat
Where to go
All these ideas developed regarding caloric
value of the food (the common currency) also
food being plants (herbivores) or prey being
sessile (predators).
How about predators?
• But for a large percent of the predators, prey
are mobile. How does this change things?
• First lets look at the predator
• How does an actively mobile prey affect the
foraging strategy of the predator?
A predator and its landscape
• Predator also has to look for food –found in
“resource patches”
• However, unlike herbivores, food moves AND
does not like to be eaten!
• So, as we saw earlier, need to incorporate not
just abundance or availability of prey but their
catchability.
• This varies across habitat types!!
Need to talk about lethality
• So unlike prey where how much you eat
depends on how fast you can bite and chew or
how rich the food patch is, a predator has to
be able to catch its food.
• Predator lethality: basically how efficient it is
in catching a prey. If your good, your lethal, if
not….
• What is predator efficiency?
Predator efficiency
• Definition: # successful captures/total
attempts
• Difficult to quantify in the wild
• Rarely ranges over 30%
• Average probably around 20%
• Is quite variable
Reasons for variability?
• Health of prey:
- Young, sick, and old more vulnerable so
hunting efficiency would be higher for these
groups
• Mid-aged healthy prey can defend themselves
• But their ability to do so varies with habitat
Habitat and predator efficiency
• Each predator has strengths/weaknesses
• Wolves: Adapted to run prey down, attack
from behind.
here
A moose in trouble!
• Go to video
Cougars and deer
• Cougars stalk their prey.
• Need to get within 20-25 meters to have a
chance.
• Need cover
Cougars and deer
• Cougars are predators of the forest and edge!
• More than 80% of the time
• in one or the other.
Habitat use by cougars
50
40
Observed
Expected
Percent
30
20
10
0
Open
Edge
Habitat type
Forest
• And they are successful!
50
45
NUMBER OF SITES
40
75%
35
30
25
20
15
10
5
0
Open
Edge
Forest
Patch quality for predator
• So high quality patches for predators are ones
where they have a good chance of making a
kill.
The landscape of opportunity
• So through the eyes of the predator, the
landscape is one of a mixture of successful
and less successful patches.
Return to our habitat patches
Now each has a success value to it for predator. Based on lethality of
predator.
How about the prey?
• Had said prey selected on level of resources.
• It is within this framework of predator
lethality that the prey must make their
foraging decisions!
• So…. Becomes not as simple as selecting the
patch with the highest food resources.
• Need to balance food resources and predation
risk.
Which is more important?
• In the past, placed most (if not all) emphasis
on resource levels.
• How long does it take to starve?
• How long does it take to get killed by a
predator?
• Food is important but not if your dead!
Predation risk
• So the risk of being killed (predation risk)
becomes overlying factor in how a prey will
use the habitat.
• What are its options?
• 1) use dangerous areas less/safe ones more
• 2) If you have to go, spend little time/use
vigilance to offset dangers/reduces feeding
efficiency
Two principle lines of investigation
1. Changes in habitat
2. Changes in the amount of vigilance.
Where risk is low:
- Use all parts of habitat
Where risk is high:
- Use the most secure areas
2. Changes in Behavior.
-Time foraging vs surveying.
Where risk is low:
- eat more and survey less.
Where the risk is high:
- survey more and eat less.
Since the 1980’s – lots of studies:
Mech, L.D. 1977. Wolf-pack buffer zones as prey reservoirs.
Science 198:320-321.
Edwards, J. 1983. Diet shifts in moose due to predator avoidance.
Oecologia 60:185-189.
Stephens, P.W. and R.O. Peterson. 1984. Wolf-avoidence strategies
of moose. Holarctic Ecology 7:239-244.
Scrimegeour G.J. and J.M. Culp. 1994. Foraging and evading predators:
the effect of predator species on a behavioural trade-off by a
lotic mayfly. Oikos 69:71-79.
Hunter, L.T.B. and J.D. Skinner. 1998. Vigilance behaviour in African
ungulates: the role of predation pressure. Behaviour. 135:195-211.
And more.…
All indicate that the prey are
adjusting their behavior
because of the risk of predation.
Our studies:
Wolves-elk: Laundré et al.
Puma-deer: Altendorf et al.
Hernández and Laundré 2005
Supported these predictions.
Elk -Wolf
Yellowstone Park
Mammoth
Swan Lake
Flat
Lamar Valley
Gibbon Meadow
West
Yellowstone
Madison
Junction
Hayden Valley
Yellowstone
National
Park
Old Faithful
Wolf Pack locations (96-97)
Wolf Pack expansions (98-00)
Grand Teton
National
Park
Towns and Tourist sites
20 km
N
Visual
Observations
Effects on Feeding Behavior
Amount of
Feeding
Amount of
Vigilance
Elk
Level of vigilance of females with calves before and after
The reintroduction of wolves in Yellowstone.
70
Females with calves in area with wolves
60
% Vigilance
Females with calves in areas originally without wolves
50
40
30
20
10
0
1
2
3
4
Number of years after wolf reintroduction
5
6
Predation Risk and
Habitat Use.
Pellet group Counts
Effect of predation risk on
Time Allocation.
3
Lamar valley
Non wolf areas
a
Y = 1.9 - 0.002 X
r2 = 0.657,P = 0.001
Number of Pellet Groups/10m 2
2
1
0
1998
NS
2
b
-100
0
100
200
300
400
500
Y = 1.06 - 0.002 X
2
r = 0.68,P = 0.003
Lamar Valley
Non wolf areas
600
Distance from Forest Edge (m)
located at 50 m intervals. Plots started 50 m into
the forest and were located every 50 m up to 500 m
into the open.
Number of Pellet Groups/10m 2
Number of pellet groups per 10 m2 sample plots
1
0
NS
-1
-100
0
1999
100
200
300
400
500
Distance from Forest Edge (m)
600
Mule Deer - Puma
Giving Up Densities
Forest
Edge
Open
Giving up densities (kg)
Graph of Giving Up Densities for two forest types
1.5
1.4
1.3
1.2
1.1
Open areas
Edges
Forest area
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
Douglas Fir
Mountain Mahogany
Habitat type
Habitat Use
Pellet surveys
Deer pellet groups per 10 m2
6
Mean deer pellet groups per 10 m2
Open
Edge
Forest
5
4
3
2
1
0
1st Yr 2nd Yr
1st Yr 2nd Yr
Juniper
Fir
1st Yr 2nd Yr
Mahogany
1st Yr 2nd Yr
Aspen
So:
Predators
not only kill
their prey…
They Scare Them!!!
So what do we have?
• Predator that has varying lethality
• Prey that responds to this by avoiding high
risk/lethal areas
In Response
Large ungulates
1. React behaviorally
a. Increased vigilance
b. Reduced feeding
2. Change their foraging strategies
a. Spend more time in “safe” areas
3. Have a poorer quality diet
a. Any shift in use will be to poorer area
All this made us think of what might be
the basic force to explain these
reactions of prey to their predators.
Fear of predation changes how they
use the landscape
as they move about the landscape
to reduce predation risk.
Thus a landscape of physical features
Or
is seen through their eyes as a landscape
of differing levels of risk or fear
The Landscapeof
of Fear
A Landscape
Fear
10
6
4
2
Pl
an
e
10
8
6
2
4
Dista
nce in
2
0
Y Pla
ne
0
in
sta
n
4
8
ce
0
X
6
Di
Predation Risk
8
here
And the game goes on
• Given all that, lets return to the predator!
• Given that it scares its prey
• Its prey respond by using safe areas more (low
lethality of the predator)
• Where should the predator hunt relative to
prey densities??
Developing views
• Commonalities in physiological and behavioral
responses to DANGERS within and among
species.