BIO375 Midterm 2

Mechanism

What cues and internal processes are the immediate cause of this expression of the behavior?

Development

What processes acted during the individual’s lifetime to cause the trait?

Evolutionary history

What sequence of events happened in ancestors leading to present day trait?

Function

What are the fitness consequences of the trait and why?

Conditions needed for selection

1.     Variation in trait

2.     Variation in biological fitness

3.     A relationship between trait and fitness

Conditions needed for selection to lead to evolution

Heritability of the trait – the resemblance between parents and offspring due to genetics

Competition

Presence of another individual has a negative effect on success (fitness)

Exploitative competition

Another individual has detrimental effect, but only by using up a common resource

Ideal Free Distribution

Individuals will distribute among patches such that energy intake rate will be equal; that is, in proportion to the quality of the patches.

Energy intake rate (R)

Quality (Q)

R=Q(individual)/D(individual)

Assumes:

Free to move among patches (no barriers or major costs)

Full knowledge of resources and competitors in each patch

Equal competitors

Example of ideal free distribution

Mallard Ducks

Bread crumbs of equal size were tossed at equal rates between two sites at the pond. The ducks were counted at each station, and were found to distribute themselves about 50/50 between both sites during this feeding cycle.

If bread crumbs were tossed 2x faster at one site (still same crumb size) the amount of ducks went down predictably at the poorer site until the rate of energy intake was equal in proportion to the patch.

If bread crumbs were tossed at equal rates but one site gains bigger bread crumbs this IDF model happens once again, but a little slower as the ducks figure out their surroundings.

How do they know where to go?

INTO MECHANISM WE GO

Mallards have a ‘rule of thumb’ to determine where to travel, matching throwing rate with number of ducks. The bread crumb size momentarily threw them off, but they adjusted.

Example of mechanism: MALLARD DUCKS

Mallards have a ‘rule of thumb’ to determine where to travel, matching throwing rate with number of ducks. The bread crumb size momentarily threw them off, but they adjusted.

Types of cues

1. Social cues – Discrete information (number of competitors)?

2. Sampling – Assess reward directly and sample patches?

3. Public information – Graded information (observe success of competitors)?

Example of mechanism: STICKLEBACK

Observer fish placed between two feeders; the control was given no food cues, so the fish stayed in the center (stickleback smells no food in the water).

Now there are six fish on one side and two fish on the other, with the observer fish in the middle. The fish seem to prefer to stick into a larger group based off of this control.

In the first exp. More food is provided to the group of 2 than the group of 6 on the other side. Where did the observer go? To the 2 fish.

Sticklebacks use public information to decide where to forage

‘Rule of thumb’

Animals can assess reward rate directly by observing competitors

Unequal competitor model

Will only be ideal free if gain per individual is same in all patches

This distribution is stable but NOT ideal free

Just like the second image here, showing a distribution of large and small fish together – equal gains between patches, but not within patches

Stable and looks like IDF, but it is not!

Different stable strategy indeed

Example for unequal competitor model: STICKLEBACKS

Measured food intake of fish, identified better competitors

Tested a mixed school of competitors with two patches of different value

Result was most often that better competitors were in ideal free, and poor competitors in ideal free, producing an outcome matching the ideal free quite closely.

The poor and better competitors were in ideal free separate from one another, two separate stable systems. This created an overall stable strategy that closely resembles a normal ideal free situation.

Example for unequal competitor model: COHO SALMON

Measured “competitive weight”: food eaten by salmon in single patch in artificial stream

Gave salmon choice of two patches, manipulated food resources in patches

They assorted close to the IDF with unequal competitors model, poor and better competitors sorting separately, but then shifted to a new unique stable strategy.

The poorer competitors began to do better than the better ones. This suggests competitive ability changes during trial or from patch to patch.

The ideal free THOMPSONS GAZELLE: foraging dispersions

Thompson’s gazelle (Eudorcas thomsonii)

Forages on heterogeneous patches of grass

Forages in loose, diffuse herds

No aggression or dominance

If in IDF:

use of patches in a consistent proportion regardless of overall density

This occurred!

But at higher densities, poorer patches seemed to be favored. Why?

Predators! More visible in poorer patches – non-foraging gazelle went there

Foraging gazelles liked to be near the non-forgaing ones for predator detection

Interference competition

Impact on another’s fitness due to exclusion from resources

Coevolution

The evolutionary change that occurs when selection on traits in a focal organism is caused by the traits of another organism and vice-versa.

Conflicting demands

When an activity simultaneously increases one component of fitness but decreases another

OR

When limited resources (e.g., time, energy) must be allocated to two or more fitness-enhancing traits

Fitness proxy example

W=SxF

S = probability of survival

F = fecundity (reproduction)

W = total fitness

Probability of not starving and probability of not being eaten both increase S

S = 1 - [Pr(starvation) + Pr(predation)]

Predation risk and foraging

Optimal activity is determined when the slops sum to zero

Balance of probability of starving and being eaten

Optimal activity level will shift with the density of food and predators

Example of predation risk versus foraging: EGYPTIAN GERBIL

Must balance between being food and eating food

SLOPE of probabilities important

Optimal resource defense

Defending a resource is both beneficial and costly.

– Benefits

• More resources (increase survival or reproduction)

• More mates (increase reproduction)

– Costs

• Energy expended

• Risk of injury

We should expect stabilizing selection: optimal territorial defense

Stabilizing selection will occur

Example for optimal territory defense: SANDERLINGS

Variation in size of area defended

Variation in amount of food and number of intruders

If there is higher food there is a steeper benefit curve

This translates to a smaller patch of territory being more optimal to defend

Less length to travel for more prey, no need to protect that extra land at the cost of possible injury

Therefore, territory should decrease when food supply increases

Negative benefit cycle

If food supply decrease they would need to increase their territory to find such food

This was supported, sanderlings in good areas have smaller territories – there are also a lot more intruders though!

How do territories respond to more intruders?

An increase cost of defense is experienced with more intruders

This would mean a shift towards smaller territory once again

Sanderlings would keep smaller territories when there are more intruders as well

So these sanderlings in better areas have smaller areas due both to an increase of food supply and an increase in intruders.

This study also found that intruder pressure is more important to sanderlings, and they will decrease their territory for this even when there is not necessarily more food to eat in their smaller patch.

If there are no intruders, even if the prey density does not decrease, sanderlings will increase their territory size as well.

Example for optimal territory defense: CONVICT CICHLIDS

Measured the consequences of territorial behavior in the lab; found that benefits of larger territory had a diminishing returns curve

The number of intruders also increase with larger territory

Once again, intermediate size maximized growth

Stabilizing selection is a girls best friend truly

G A M E T H E O R Y [Hawk–Dove Game]

Evolutionarily Stable Strategy: A behavior that has higher fitness than any other and so cannot be invaded by another behavior,

or

the stable mix of behaviors where no particular type can do better than the other.

Let us consider two behavioral types:

The HAWK: aggressive, will fight opponent if also aggressive

The DOVE: not aggressive, will run away if opponent is aggressive

HAWK always wins against DOVE, no injury to either

HAWK beats HAWK 50% of the time, risk of injury if loses

DOVE beats DOVE 50% of the time, pay some cost of display

Assumptions

– Everyone within a strategy is equal

– No one knows what opponent will do

– Strategies are fixed (genetic)

Fitness variables

V = Resource gained by winner

C = Cost of injury to loser if there is a fight

For HAWKvHAWK:

Each hawk will have: V/2-C/2

The resource gained and cost is divided by two because of the inherent interaction between two animals, and also the 50% chance of losing

For HAWKvDOVE:

The dove will have: 0

The hawk will have: V

The dove will always flee, gaining and losing nothing

The hawk will always win, with full resource gained

For DOVEvDOVE

There is no inherent cost so;

Doves will both have: V/2

The resource gained is cut in half due to the 50% chance of losing between the two birds as well

Hawk is better against Hawk than Dove is if C < V

[for my math illiterate homies: if cost is less than resource gained]

Dove is better against Hawk than Hawk is if C > V

[if the cost is greater than the resource gained]

Hawk is better against Dove than Dove is if V > 0.

[if the resource gained is greater than 0]

Hawk is the evolutionary stable strategy if resources gained is greater than the cost associated

Dove, though, is NEVER an evolutionary stable strategy [sorry dove]

This is an example of FIXED strategy: one response every time (genetic)

And Pure ESS: all one type in population

Negative Frequency Dependent Selection

Relative fitness depends negatively on frequency of that strategy.

HAWKvDOVE when stable strategy is two equal strategy’s instead of one over the other

H = hawk

1 - H = dove

H(V-C)/2 + (1-H)V = (1-H)(V/2) + (H)0

The first part of the equation is fitness of hawks, and the second part is the fitness of the doves

‘H(V-C)/2’ is fitness of HAWKvHAWK

‘(1-H)V’ is fitness of HAWKvDOVES

‘(1-H)(V/2)’ is fitness of DOVESvDOVES

‘(H)0’ is fitness of DOVESvHAWKS

This equation produces a mixed ESS

Stable polymorphism of fixed strategies

Fixed Strategy

Genetic

Pure ESS

All one type in population

Mixed ESS

Stable polymorphism

Stochastic Mixed Strategy

Exhibit one of 2+ tactics with given probability

Resident wins phenomena?

In competition the resident of the territory typically wins as they have more to lose – they are aware of the wealth of resources and will fight harder to keep them

GAME THEORY H+D ADDED: BOURGEOIS

Hawk when resident, dove when intruder

What if population is all hawk?

Both bourgeois and dove invade!

What if population is all dove?

Both hawk bourgeois invade!

What if population is bourgeois?

Nothing can invade, so bourgeois is ESS!

Conditional Mixed Strategy

If condition A, then do tactic “Y”, otherwise do tactic “X”

Example: if owner plays hawk, the intruder plays dove

VALUE RESOURCE HYPOTHESIS; resident always wins example: REDWING BLACKBIRD

Removed territory owner, let replacement take over, then released owner back on territory a variable amount of time later, observed outcome

If bourgeois the replacement should always win

If the original owner has higher RHP, then they should always win

If there is value asymmetry, then the original owner should win after very short delay, but as the time away from their home increases the replacement should start to win

This is what happened!

The owner that was removed for only 1-4 days [with a new bird moving in and living there for those 1-4 days] always took back their territory, but the owner than had been removed from the territory for 6-7 days [and the new bird living there for those 6-7 days] did not. After so many days the new bird finds value in the territory, and the previous owner not as much as they had been away too long.

A third treatment was then utilized to strengthen the test!

The owners are removed for 8-10 days, but two different replacements are there over that span of time. The first replacement is left there in the territory for 6-7 days, then removed. A new bird moves in for 2-3 days after.

The owners once again reclaimed their nests! The newest residents hadn’t had long enough to value the territory they were in, and the owners [even though they had been away a great amount of time] still won.

This supports value resource hypothesis!

RHP

Resource holding power

Alternative types of assessment

Self assessment:

Contestants know how long they will fight, but don’t know opponent

Duration of fight thus depends only on loser’s RHP.

Sequential [mutual] assessment

Each contestant acts like “Dove” at first and displays, goal to assess RHP of rival (mutual assessment)

Contests escalate in intensity [become more hawk-like] until a difference in RHP is detected

Predictions:

i. Contest duration negatively related to difference in RHP

ii. Intensity of fight is negatively related to difference in RHP

mutual assessment example: FIDDLER CRAB FIGHTS

Burrows in sand are highly valued in fiddler crabs – for protection and attracting mates

Males defend them from intruders

In this exp. They staged fights and measured the factors that influence their duration

Duration of fight = DOF

DOF is negatively associated to ratio of claw sizes, which suggests mutual assessment

If there is bigger disparity between the winner and losers claw size, or a bigger difference, the fight will be shorter

Example for mutual assessment: MANTIS SHRIMP

They defend their burrows from others

Use their hard claw to fight

Size/strength is important to winning, fights can lead to serious injury

They first display their tail and claw before fighting

Shrimps molt every month, so there is 2-3 days where they are vulnerable and will not win or withstand a fight no matter their size

What should they do?

They still threaten!

Molting shrimp ‘bluff’ to their opponents and still show their tails, despite not being able to fight

They are more likely to display if the intruder is slightly smaller than if it is larger

As the intruder gets bigger than them they are more likely to flee, and smaller they are more likely to bluff

Individuals who have experienced a bluffer do not alter their behavior to molting shrimp

Why not?

They don’t know if another shrimp is molting or not!

They cannot assume whether or not a Shrimp is molting before the fight

Better to lose to a bluffer than get serious injury to a bigger nonbluffing shrimp

Imput matching rule

animals should distribute themselves across different patches of resources in a way where the ratio of individuals in each patch directly matches the ratio of the resource input rate in that patch

Explotative competetion

Individuals indirectly decreasing resources from one another in a patch due to limit of resources in that area.

Interference competition

When an individual directly prevents another from accessing resources

Communication

Transfer of information from signaler to receiver (trait in one animal modifies the behavior of another).

Signaler

Manipulate receiver [dishonesty]

Receiver

Avoid manipulation [enforce honesty]

Mutualism

Signaler and receiver both benefit from the transfer of information

COMMUNICATION EXAMPLE: VERVETS

Live in groups of 10-50, and use a variety of vocalizations

Different types of calls:

Predator alarm calls [snake call, eagle call, leopard call]; given when a predator is seen

Different behaviors associated with these three calls to avoid predation

These calls benefit both the signaler and receiver; mutualism in predator calls

There are also three calls [grunt, chutter, wrr] given to alert that another group is approaching, causing others to look at the caller and then scan in direction the caller is looking at

Deception:

A low ranking male has been seen to give leopard predator call when a group is approaching to avoid interaction with that group

Calls are used inappropriately about 2% of the time

The exp.!

They played back intergroup calls of a specific monkey in the group whenever there was no other group around to observe their response

The group learned this individual call and grew to ignore it

They also ignored all other group calls of that same individual

They responded to another individuals calls just fine, though

The call itself is not the issue, it is that they no longer believe the individual

They can distinguish between individuals calls and ignore those who ‘cry wolf’ often

Predator calls are ALWAYS responded to, though, no matter how many false ones

It would be too costly to ignore a predator call if it were to be true!

Mutualistic communication example: HONEYBEES

Waggle dance

They are not in competition, and foraging efficiency increases when there is effective recruitment to good food sources

They need to:

Get other bees to go to source

Get other bees to efficiently find source

Waggle dance!

Communicates direction and distance

Strong relationship between angle of waggle dance from vertical and direction of food

Outside of the hive the dance is oriented relative to the light

Distance is encoded into the dance

How do we know receivers understand?

Provided rich sugar solution with odor at a foraging station.

Foragers coming to station had eyes painted over, could still orient to sun in middle of day

In hive, had adjustable light bright enough to overwhelm orientation to gravity in normal bees, but not painted bees.

Progressively shifted the angle of the light

Counted the number of bees coming to stations with same type of sugar water and odor

-if bees use orders the angle of light will make no difference

-if bees use information in dance, because foragers are misdirecting dance relative to recruits when light is at an angle they will miss the food at the specific angle of the light

Result? Recruits ended up at the predicted angle of the misdirected waggle dance!

Controls with unpainted eyes kept the bees going to the right station

Bees do have a symbolic language and use this to mutually transfer beneficial information to others!

GAME THEORY: COMMUNICATION [mutualism]

Honest vs. Deceptive signal when pertaining to Gullible vs. Skeptical organisms

This is what occurs for mutualism!

Honest signals always receive benefit from a gullible individual

Honest signal signalers receive no gain from a skeptical individual, and a skeptical individual loses when rejecting an honest signal

Deceptive signal is a lose-lose situation on a gullible individual when it pertains to mutualism

Deceptive signalers lose and skeptical receivers gain in an interaction between the two.

GAME THEORY: COMMUNICATION [conflict]

Honest vs. Deceptive signal when pertaining to Gullible vs. Skeptical organisms

This is what occurs for conflict!

Honest signals always receive benefit from a gullible individual

Honest signal signalers receive no gain from a skeptical individual, and a skeptical individual loses when rejecting an honest signal

Deceptive signalers receive a big gain over gullible receivers [who lose]

Deceptive signalers lose and skeptical receivers gain in an interaction between the two.

Conflict

Favored trait in one individual is costly to another

Conflict gradient

creates additional variation in fitness in receivers

Conflict example: SISKIN

Siskins must decide whether to approach resource defended by another Siskin

Black throat patch provides info. On opponents relative status

The consequence of errors may influence both the response of the Siskin and the utility of the signal

Sources of error in discrimination

Relationship between signal and ability

Receiver’s estimate of patch size

Types of error (Should siskin ATTACK?)

False negative (Opponent’s actual ability is worse than perceived, so siskin avoids a fight it could have won)

False positive (Opponent’s actual ability is better than perceived, so siskin gets into a losing fight)

Types of error (Should siskin DEFER?)

False negative (Actual ability is better than perceived, so siskin gets into a losing fight)

False positive (Actual ability is worse than perceived, so siskin avoids an encounter it would have won)

Receiver cannot simultaneously minimize both types of error given same constraints on perceiving signal

Errors in discrimination

Sources of variance

Relationship between signal and ability

Receiver’s estimate of trait

Error types in discrimination

False positive and false negative

What these are depend on the trait and relative question

For example

Should A fight?

False P: underestimated opponent, A is beaten to a pulp

False N: overestimated opponent, A avoided fighting a wimp

Conflict example: BROWN HEADED COWBIRDS

Why dont parents discriminated against cowbirds?

Let’s think of the consequences of errors in discrimination!

What if the phenotypic appearance of the cowbird egg is very similar to that of their own

Could they risk a false positive, kicking their own babies out of their nest, over the false negative, raising a cowbird?

Rejectors tend to have eggs very different from cowbirds

Acceptors tend to have eggs very similar to cowbirds!

Coevolutionary arms race example: EUROPEAN CUCKOO BIRD

This bird adapts their parasitic eggs to the host eggs to cause it to be too costly to kick their eggs out of the nest!

The eggs just look too similar, the false positive chance is too high, and they raise the parasite hatchlings.

Cost of signaling example: FRUIT FLIES

Even though signaling can help reproductive success, there can also be a cost associated

Male fruit flies congregate and compete for female mates in group

Release pheromone streaks while displaying

Better quality males release more pheromone

Exposing males to other males resulted in more pheromone production and shorter lifespan in comparison to solitary males or those exposed only to females

Cost of signaling example: Tungara Frog

Males give two different songs: “Tun,” and “Tun chuck”

Females prefer “Tun chuck,” but so do predators!

Bats hear this call better

Males

Producers of many small, mobile gametes

(small, numerous gametes) are most often limited by the number of female gametes (and females) encountered (selection favors increasing the number of zygotes fertilized)

Females

Producers of a few large, immobile gametes

(small number of large gametes) are most often limited by the total resources they can devote to gametes and to their size (selection favors increasing zygote survival).

Anisogamy

Dimorphism in gamete size

Isogamy

No dimorphism in gamete size

Gamete size equation

R =. Resources to devote to gametes

X = gamete amount

R/X = gamete size

If R/X is large = X must be small

If R/X is small = X must be large

This is a fundamental conflicting demand between size and number.

Gamete Size a trade-off between benefits of producing more offspring (with smaller gametes) and benefits of producing better offspring (bigger gametes)

Selection favors both smaller and larger gametes, but it is much stronger on small gamete-producers than on large.

Disruptive selection!

Small gamete producers favored because they contribute to more zygotes

Large gamete producers favored because their zygotes survive better

This is how we arrive to anisogamy!

Polymorphism in gamete size

As small gamete-producers make more, even smaller gametes, this is costly to large gamete-producers but creates selection among them favoring even larger gametes

Disruptive selection

Traits selected are both of the extremes

Visually the graph goes from an ‘n’ shape parabola to a system of two humps as the extreme traits are separated and select for, and the intermediate is selected against.

Looks kinda like an ‘m’

Evolutionary Conflict

When a beneficial trait in one organism has a detrimental effect on another

Examples:

Predator/prey

Fighting

Antagonistic communication

Anisogamy

Obligate anisogamy

Why don’t large gametes fuse with other large gametes?

THINK LIKE GAME THEORY

When a preference like this first arises, it will be rare:

1. Big gametes with preference will have trouble finding other big gametes with a preference

2. Because of the numbers of small gametes around, most big gametes will be fertilized already

3. Like fusing with like will lead to inbreeding—reduces genetic variation which reduces the advantage of sex.

SEXUAL SELECTION

The relationship between a trait and mating success [a component of total fitness]

We need

1. Variation in trait

2. Variation in mating success [a specific component of fitness having to do with the number of zygotes produced]

3. Relationship between the two

Evolution vis SS occurs when the trait is HERITABLE

Variance

sum of the squared deviations from the mean (Σd2) divided by the number of observations (n)

Variation in males and females example: RED DEER

High variance in mating success means many males do not get matings. Identical to many males dying.

Force of sexual selection affects morphology, behavior, and rate of speciation.

Intrasexual Selection

Male-male competition

Intersexual Selection

Female choice

fitness proxies

measure of fitness that meets 3 criteria

1 – must be linked to goal

2 – have a reasonable link to true fitness

3 – be reasonably easy to measure

Fitness

Lifetime production of offspring

Sperm competition

a process where sperm from different males compete to fertilize a female's eggs