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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 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 behavior
Behavior 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.
Innate behavior: migratory
orientation in blackcaps
Blackcaps from SW Germany migrate in
SW direction and those from Hungary in a
SE direction.
Innate behavior: migratory
orientation in blackcaps
Members of two populations crossed and
produced offspring.
Offspring orientation tested in Emlen
funnel.
Mean orientation of offspring south.
Strong evidence that there is genetic
control of orientation
Inner ring
Adults.
Outer ring
Offspring.
Environment modifies behavior
Habituation. Loss of responsiveness to
stimuli that do not convey useful
information (“cry wolf” effect).
Environment modifies behavior
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.
Environment modifies behavior
Spatial learning. Many animals modify
their behavior depending on the
environment they live in.
In stable environments landmarks are useful
for navigating.
Environment modifies behavior
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.
Foraging pathways of individual Drosophila larvae
Rover
Sitter
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
Enhancing reproductive success
Investment includes energy invested in young and
time spent caring for and guarding the young.
Choosy sex has limited capacity to produce more
young.
Enhancing reproductive success
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 competition
Males 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 of
Paradise 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 if
Br - 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.
Calculating relatedness
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.
Calculating relatedness
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 relatedness
Sibling1 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.
Belding’s Ground Squirrels
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.
Belding’s Ground Squirrels
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.