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to the top.Biology 441. Animal Behavior
Midterm II. 14 November 1996
150 points - 5 points for name on top of each page.
40 pts. 1. Define and provide an example of each of the following
(5 pts. each):
a. selfish herd
group in which individuals use each other as a shield against predators with individuals in the center accruing the highest protection
e.g., starling flock, center birds
b. Mullerian mimicry
convergent evolution of color patterns of two or more distasteful or noxious species, e.g., black/yellow patterns of many poisonous hymenopterans
c. Convergent evolution
Evolution of similar traits in species of different evolutionary lineages due to common selection pressures, e.g., warning color patterns in reptiles and insects
d risk-prone foraging
preferring variable rather than constant reward rates, e.g., premigratory
or food-stressed birds
e. badge
conventional signal of social status which is not costly to produce and thus may or may not be honest, e.g., throat patches of Harris Sparrows and male House Sparrows
f. cheating
signaling that deceives receiver to the benefit of the signaler and potentially at a cost to the receiver, e.g., false alarm calls at feeders by subordinants in species of flocking birds
g aposematic coloration
conspicuous warning coloration of distasteful or noxious species,
e.g., bright color striping patterns on poisonous snakes
h dilution effect
local overabundance of prey in relation to predator ability to consume
them (predator swamping); reduction in probability of predation on a per
individual basis as size of the prey group increases. Flocking birds and
herding ungulates.
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(15 pts.) 2. Why does Bernd Heinrich believe that ravens "yell"? How did he come to settle on this hypothesis? How did he discount other hypotheses?
see Alcock, pp. 257-260
Yelling at food sources is energetically costly and potentially attracts competitors, both other ravens and other species. Heinrich believes that if ravens are floaters they yell to attract enough other floaters to make it impossible for the territory-owning pair to drive them away. He found that owners do drive away single intruders, owners do not yell, owners are unable to repel several intruders, and intruders do yell. Also, either silent individuals or pairs or noisy crowds of ravens exploited baits.
You should discuss both of the following hypotheses. Heinrich originally
thought that ravens yelled to attract mammalian carnivores, e.g., coyotes,
to the carcass to make internal portions accessible, but he found that
ravens yell at already opened carcasses. Second, he noticed that ravens
very cautiously approached carcasses, and he thought that perhaps they
yelled to attract other ravens to dilute the risk of predation. However,
ravens yelled even when large numbers already had aggregated at the carcass,
contradicting this hypothesis.
(10 pts.) 3. Describe wolf pack buffer zones and hypothesize
why they occur. Would it be appropriate to argue that buffer zones have
evolved to keep deer from going extinct, thus permitting the long-term
persistence of both wolves and deer? Why or why not?
Buffer zones are areas on the perimeters of wolf territories that
wolves seldom use and where white-tailed deer are more likely to survive
when deer at low densities. Wolves rarely hunt or patrol these areas because
they risk injury or death if they encounter members of neighboring packs.
Buffer zones likely occur because the potential benefit of obtaining a
meal, e.g., a deer, is outweighed by the potential cost of injury or death
of an encounter with neighboring wolves.
Long-term persistence of deer is a consequence, but should not be
considered a cause, of wolf avoidance of boundary areas. If some packs
avoid boundary areas to preserve deer, neighbors who exploit the deer will
have higher success, i.e., preserving deer would not be an evolutionarily
stable strategy.
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(20 pts.) 4. Use the following graphs to answer the following questions. Starting at 0 residents, in (a) show the sequential patterns of settling for the first 12 individuals attempting to settle in a particular area where two habitats are available. Once those 12 individuals have settled what is the approximate expected fitness of residents of habitat A? _3.2____. of habitat B?___3.2___. What is this pattern of settlement called?___ideal free distribution_____.
Is there any real world example that seems to fit this outcome?
Explain.
Great tits in the Netherlands that inhabit mixed woods and pine woods--breeding success is the same for mixed woods, where the birds settle preferentially and at higher densities, and pine woods.
Female red-winged blackbirds returning to breed in an early spring--later
arrivals can settle in best areas because more dominant females have started
to incubate and can't chase them off--females in preferred and secondary
habitats have equal fitness in such years.
Starting at 0 residents, in (b) determine the sequential patterns of settling of the first 10 individuals attempting to settle in the area. Once those 10 individuals have settled, what is the approximate expected fitness of residents of habitat A?__5.7___of habitat B?____4.0____.What is this pattern of settlement called?____ideal despotic distribution_____.
Is there any real world example that seems to fit this outcome?
Explain.
Great tits in mixed woods and hedgerows in England. Mixed woods are
preferred and breeding success is higher there. Female red-winged blackbirds
arriving synchronously in a late spring--dominant females chase off subordinants
who then settle in poorer habitats and have lower success.
Sequential patterns--in (a) show numbers and note that once densities
in A cause suitability of A to decline to basic suitability of B, both
will then fill alternately. In (b) show sequential pattern of filling on
dotted lines and compute success using solid lines.
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(15 pts.) 5. Describe how vigilance behavior varies with respect to flock size for starlings in the center of the group and for those on the edge. Are there likely correlated differences in feeding rates? Why or why not? Are there any additional differences that would be important to individuals in the group? Explain.
For center birds vigilance rates are high in small flocks but decrease as flock size increases. For edge birds vigilance rates are relatively high and vary little with respect to group size. Foraging rates are probably inversely related to vigilance rates--birds in the center of large flocks likely have the highest foraging rates because they are spending less time being vigilant.
The selfish herd is likely of prime importance: edge birds provide
cover for center birds, particularly in large flocks.
Note that the dilution effect applies to all individuals in the group.
Also, starling flocks occur in the nonbreeding season and are foraging
flocks, not breeding colonies.
(15 pts.) 6. In prides of 3-4 lionesses, generally all of the
lionesses hunt together. Consider 3 reasons why this may be so and provide
evidence that supports or contradicts each reason.
1. maximize food intake/individual lioness--not true in Serengeti
where individuals in either small (1-2) or large hunting groups have the
highest success--unless group size is about 6 or higher, lionesses in groups
don't take down larger prey than lionesses hunting alone or in groups of
2.
2. Coordinated hunting: applies where Stander conducted his studies
but not where Packer and others conducted theirs.
3. Protection of young from infanticidal males--shown to be effective
(on the Serengeti, single lionesses typically lost all young to infanticidal
males).
4. Protection of kills from hyenas and other scavengers (and appropriation
of carcasses from other predators)--likely important but no quantitative
data
5. Protection of territories from neighboring groups of lionesses--likely
important because relative size of groups seems important in determining
outcomes of encounters between neighboring prides.
6. Kin selection--feed kin rather than other species--possibly important
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(15 pts.) 7. Describe and contrast the resource-holding and payoff asymmetry hypotheses in relation to territoriality. What evidence favors one hypothesis over the other? Could you better distinguish between the hypotheses if you studied migrant birds as they returned to set up territories instead of after territories already have been established?
Resource holding potential (RHP): winners of contests for territories are those that are stronger, bigger, or in better condition. Because of their better ability to hold resources they can prevent take-over attempts by weaker individuals. Payoff-asymmetry (PAH): benefit:cost ratio differs for owners and challengers and favors owners, e.g., because costs against established neighbors decrease the longer the territory is held and familiarity increases the longer the territory is held.
If individuals holding territories are in better condition than those that don't, the RHP hypothesis is supported and this is true in many cases that have been studied. However, which comes first: better condition or a territory that permits better condition? Experimental removal and later release of territory owners has been the approach to evaluating the PAH, and longer delays result in longer fights and more wins by the new owner, supporting the PAH. However, holding the first owner in captivity may decrease its condition, biasing the results.
Examining returning migrant birds would help distinguish between the 2 hypotheses. Is ownership determined by condition at the time of territorial establishment, supporting the RHPH? Are birds that attempt to retain the same territory between years more successful than expected on size and condition alone, supporting the PAH?
(15 pts.) 8. Define information center. Considering colonial species, provide one example that fits the definition and one that does not. Explain the contrast between the two examples.
An information center is a place, e.g., colony or roost, where conspecifics provide information about distant sources of food (not necessarily intentionally).
Two examples that fit this idea are (1) ospreys returning with a schooling fish to their nest; subsequent departures by others in the colony are in the direction from which the bird came, and (2) cliff swallows returning with insects in their bills who are then followed when they depart again to forage.
Barn swallows and most seabird colonies aren't information centers. For example, murres depart in random directions and don't leave soon after neighbors return.
There are several possible reasons: first, direction of return may
be a good indicator only if schools of fish are nearby but not if they
are far away. Second, it is not always obvious whether an individual has
been successful. Third, following a successful individual would be impossible
if it doesn't depart again for several hours.
Had you been exposed to the Prisoner's dilemma before? If so in what classes? No: 12, Yes: 14, 3 no answer
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