Behavioral Ecology Study of how behavior is controlled, evolves, and enhances survival and reproductive success of organisms. Behavior is what an organism

Behavioral Ecology

Study of how behavior is controlled, evolves, and enhances survival and reproductive success of organisms.

Behavior is what an organism does and how it does it.

Proximate and Ultimate Questions

Proximate questions focus on mechanisms and development of behavior.

They are “how” questions.

For example: How does a bird learn its species song? Or How does a plant know when to produce flowers?

Proximate questions

Possible hypotheses that address these “how” questions include:

Males learn their species song by listening to what their father sings and

Flowering in plants is triggered by increasing daylight.

Ultimate questions

Are “why” questions.

They ask why natural selection favors the behavior and ultimate hypotheses suggest that the behavior enhances fitness.

Ultimate questions

For example: Why do female birds prefer males with brighter plumage?

Or Why do birds look up occasionally when they are feeding?

Ultimate questions

Ultimate hypotheses that might address these “why” questions include:

Females prefer males with brighter plumage because such males possess genes that confer disease resistance and

Birds look up to scan for predators, which enhances their survival.

Ethology

Field of Behavioral Ecology pioneered by ethologists in middle of 20th century who included Niko Tinbergen, Karl von Frisch and Konrad Lorenz (shared 1973 Nobel Prize).

They carried out many well known studies including studies on fixed action patterns and imprinting.

Fixed action pattern (FAP)

Fixed Action Pattern is a sequence of behaviors that is essentially unchangeable and once begun is completed.

Tinbergen studied FAP in three-spined sticklebacks. Males have red bellies and defend territories from other males. But they will attack any small unrealistic model fish so long as it has a red belly.

Fixed action pattern (FAP)

Red belly is a “releaser” that causes stickleback to initiate its defensive response.

Fig 51.4

Imprinting

Lorenz carried out famous studies of imprinting behavior in graylag geese.

Young goslings imprint on their mother in first few days of life, follow her and learn basic goose behaviors.

However, goslings will imprint on a human substitute (or an object such as a toy truck) if exposed to the correct stimuli (large object that moves away slowly).

Imprinting occurs in a short sensitive period and is irreversible.

Fig 51.5

Genetic components of behaviorBehavior is affected by both genes and the environment.

In some cases there is variation between individuals in their behavior as a result of differences in environmental influences.

In other cases individuals in population show little variation despite differences in environmental influences. These are innate behaviors

Innate behavior: Kinesis

Kinesis: strong change in activity or turning rate in response to stimulus.

E.g. Woodlice become more active in dry areas and less in humid areas. Helps to keep them in moist areas and move out of dry.

Fig 51.7a

Innate behavior: Taxis

Movement towards or away from a stimulus.

Cockroaches demonstrate negative phototaxis (move away from light).

Trout demonstrate positive rheotaxis and face towards the current in a stream.

Fig. 51.7b

Innate behavior: migratory orientation

in blackcaps

Innate behavior: migratory orientation in blackcaps

European blackcaps migrate to Africa.

Can assess direction birds choose to migrate using an Emlen funnel.

Birds spend most time in part of funnel that faces in direction they want to migrate.


Blackcaps from SW Germany migrate in SW direction and those from Hungary in a SE direction.


Members of two populations crossed and produced offspring.

Offspring orientation tested in Emlen funnel.

Inner ring

Adults.

Outer ring

Offspring.

Mean orientation of offspring south. Strong evidence that there is genetic control of orientation

Environment modifies behavior

Habituation. Loss of responsiveness to stimuli that do not convey useful information (“cry wolf” effect).


Associative learning. Many birds learn quickly that Monarch butterflies taste foul and will avoid them after an initial experience.

Rats will permanently avoid a food if after eating some of it they subsequently become nauseated.


Spatial learning. Many animals modify their behavior depending on the environment they live in.

In stable environments landmarks are useful for navigating.


Sticklebacks modify their behavior with landmark stability.

Fish taken from ponds (where landmarks are more stable) make more use of landmarks than fish taken from streams in lab experiments.

Behavioral traits evolve by natural selection

Agelenopis aperta a funnel web spider occurs in both desert and riparian (riverside) woodland.

Desert spiders (which occur in food-poor habitat) are much more aggressive and attack potential prey much more quickly than riverine spiders.

51.19

Behavioral traits evolve by natural selection

Differences between spiders persist in the lab and in lab reared offspring so behavioral difference has a genetic basis.

Selective reason for difference appears to be that food and predators more common in riparian habitat. Risk of missing a meal a greater cost for desert spiders than their risk of predation. The reverse is true for riparian spiders.

Behavioral traits evolve by natural selection. Drosophila foraging.

Two alleles in a gene for foraging forR and fors.

forR : rover larva moves more than average; fors sitter larva moves less than average.

Rover

Sitter

Foraging pathways of individual Drosophila larvae

Behavioral traits evolve by natural selection. Drosophila foraging.

In lab studies in low density populations of Drosophila fors allele increased in frequency. Opposite was true in high density populations.

In low density populations fors individuals did not waste energy traveling long distances for food. In high-density populations forR allele caused larvae to move beyond areas of food depletion.

Many other single gene effects found in Drosophila.

E.g.

Stuck – males don’t dismount after normal 20-minute copulation

Coitus interruptus - male copulates for only 10 minutes.

Natural selection favors behaviors that increase survival + reproduction

Differences in reproductive success of different genotypes result in evolution. This is natural selection.

Behaviors that increase mating opportunities and survival will enhance reproductive success.

We expect natural selection to favor behaviors that enhance survival (e.g. efficient foraging behavior and avoidance of predators) and that results in higher reproductive success (e.g. choosing high quality mates, avoiding cuckoldry)

Optimal foraging

A lot of work has been carried out on how organisms maximize their food intake while minimizing their energy expenditure and risk of mortality.

Expectation underlying this work is that organisms will be efficient and forage optimally.

Zach’s crow work

Crows feeding on whelks (marine snails) fly up and drop the whelks on rocks to break them.

Height from which a shell is dropped affects its probability of breaking.

Dropping from greater height increases probability of breaking shell, but it costs energy to fly up.

Reto Zach studied crows and predicted they would fly to a height that, on average, provided the most food relative to the energy needed to break the shell.

Zach dropped shells from different heights and for each height determined the average number of drops needed to break a shell.

Then he calculated total flight height (number of drops x height of each flight) as a measure of the energy needed to break a shell.

Zach predicted a height of 5m would be the optimal flight height. Observed height crows flew to was 5.23, a close match.

Fig 51.22

Minimizing predation risk while foraging.

There are numerous ways in which organisms attempt to minimize their risk of predation.

These include: avoiding habitats that are the most dangerous, foraging in groups and spending time looking for predators.

Many animals group together to avoid predation.

Grouping increases chances a predator will be spotted before it can attack. Grouping also increases time spent foraging as individuals have to scan less often in a group.

Experiments by Kenward using a trained Goshawk showed that as flock size increased woodpigeons detected an

approaching bird at greater distances.

Enhancing reproductive success

Males and females generally differ in optimal reproductive strategies.

The sex that invests more in the offspring (usually female) is the choosy sex.

Hamster egg and sperm


Investment includes energy invested in young and time spent caring for and guarding the young.

Choosy sex has limited capacity to produce more young.


Choosy sex maximizes reproductive success by requiring other sex to provide resources (e.g. territory, food) or by choosing the best possible mate for its genes.

Non-choosy sex maximizes reproduction by mating more often.

Monogamy

Type of mating system observed influenced by whether both parents needed to rear young.

In most birds young need lots of care so monogamy is common and both parents participate in caring for young.

Polygamy

When one sex can care for the young polygamous mating systems are common (e.g. most insects, elk, elephant seals, some birds e.g. grouse, peafowl, jacanas) and individuals mate with multiple mates.

Bull elk and harem

Competition for mates

Generally, members of the non-choosy sex compete to either control females by defending them (e.g. elk, elephant seals, phalaropes) or to attract females to mate (peafowl, grouse).

By maximizing number of times they mate they maximize reproductive success.

Sperm competitionMales compete not only to mate with females, but frequently engage in sperm competition as well.

More sperm a male can insert the higher his chances of fertilizing eggs (like a lottery).

In species with lots of sperm competition males have proportionally larger testes than males of monogamous species.

Sperm competition

Males also commonly remove other males’ sperm (e.g. damselflies have a penis with spines), plug up females’ reproductive tract (many insects) or guard females against other males.

Alternative mating strategies

Paracerceis isopods (a type of crustacean) live inside sponges.

There are 3 genetically different male types.

Alternative mating strategies

Alpha males large and defend harems of females.

Beta males pretend to be females.

Gamma males are tiny and sneak inside harems undetected.

Mate choice

Females are very choosy about which male they mate with.

For example, in polygynous species, such as sage grouse, a few males obtain almost all the matings and most males fail to mate.

Female birds assess male plumage quality (symmetry and color) and display quality (duration and intensity) in evaluating males.

(Male Raggiana Bird ofParadise displaying.)

Male display and male quality

Considerable evidence that male’s ability to grow attractive plumage and engage in vigorous displays are indicators of males genetic resistance to disease and parasites.

By choosing such males, females ensure their young will receive high quality genes.

Similarly, female stalk-eyed flies

prefer males with the longest eye stalks.

Male display and male quality

Various genetic disorders are correlated with flies inability to develop long eyestalks. Females who avoid such males enhance genetic quality of their offspring.

Altruistic Behavior

Easy to see how selfish behavior (e.g. not sharing food) could enhance an organisms reproductive success.

Altruistic behavior in which an organism increases another organisms reproductive success while reducing its own is harder to explain.

Altruistic Behavior

For example, many animals give alarm calls that warn others of a predator but put the caller at risk.

In bees, ants and other social insects many individuals do not reproduce themselves but assist another individual (the queen) to reproduce.

Altruistic Behavior

Key to understanding this is to realize that altruistic behavior is not randomly directed.

It is selectively directed towards relatives.

Relatives share genes and by helping relatives, an organism helps pass on its own genes.

Altruistic Behavior

Inclusive fitness: total effect an organism has on proliferating its own genes by producing its own offspring (direct fitness) and aiding other close relatives to produce offspring (indirect fitness).

Inclusive fitness = (direct fitness + indirect fitness).

Hamilton’s rule and kin selection

W.D. Hamilton proposed a simple rule predicting when natural selection would favor altruistic behavior.

Hamilton’s Rule

Hamilton’s rule states that an allele for altruistic behavior will spread ifBr - C >0

Where B is benefit to recipient and C is the cost to the actor. Unit of measurement for B and C is surviving offspring. r is the coefficient of relatedness between the actor and the recipient,

Hamilton’s Rule

Altruistic behaviors are most likely to spread when costs are low, benefits to recipient are high, and the participants are closely related.

Altruistic Behavior

Calculating relatedness.

To figure out how closely related two individuals are we need to calculate the probability that they share any given allele.

Calculating relatedness

Alleles are different versions of a gene (e.g. a gene for eye color can have many different alleles blue, green, brown, etc.)

You have two alleles for every gene (ignoring those of the X and Y sex chromosomes) one copy of which you got from your mother and one from your father.


For each gene your mother had two alleles and you received a copy of one of them. Therefore, you share 50% of your alleles with your mother. Hence the degree of relatedness (r) between you and your mother is 0.5.


To figure out r for two individuals is fairly simple.

First, identify the two individuals most recent common ancestors (for you and your full sibling these would be your two parents).

Second, for each path connecting the two individuals count the number of steps (n) connecting them.

Calculating relatednessSibling1 to mother to sibling2 is two steps,

To calculate r for that pathway use the formula: r = (½n). Thus, r = ½2 = ¼

However, siblings also share a father so you need to add the results from the two pathways together. Hence relatedness of two full siblings is ¼ + ¼ = ½.

Kin Selection

Natural selection favoring the spread of alleles that increase the indirect component of fitness is called kin selection.

Kin selection is expected to operate most strongly among close relatives

Belding’s Ground Squirrels

Belding’s Ground Squirrels breed in colonies in Alpine meadows.

Males disperse, but female offspring tend to remain and breed close by. Thus, females in colony tend to be related, but males other than offspring are not.


Long term study by Sherman of marked animals of known relatedness.

Analysis of who called showed that females were much more likely to call than males.


In addition, females were more likely to call when they had relatives within earshot.

Reciprocal Altruism

Some animals occasionally behave altruistically towards non-relatives.

Such behavior is adaptive if the recipient is likely to return the favor in the future.

Reciprocal altruism

Reciprocal altruism most likely in social animals where individuals interact repeatedly.

Reciprocal altruism in Vampire bats

E.g. Vampire Bats. Feed on blood and share communal roosts.

Bats may starve if they fail to feed several nights in a row.

However, bats who have fed successfully often regurgitate blood meals for unsuccessful bats.

Reciprocal altruism in Vampire bats

Cost of sharing some blood is relatively low for donor bat but very valuable for recipient.

Research shows that Vampire bats share with individuals who have shared with them previously and with individuals they usually share a roost with.

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Behavioral Ecology Study of how behavior is controlled, evolves, and enhances survival and reproductive success of organisms. Behavior is what an organism