(Summary of the discussion is given in italics)
1. At a superficial level, the occurrence of altruism in many species is at odds with what we've learned about natural selection. Please discuss three models that can explain the maintenance of altruism despite the fact that the altruist incurs a direct cost while others in the population benefit.
a) kin selection- altruist derives indirect benefit from helping relatives. this increases the altruist's inclusive fitness. Because they share genes, helping a relative leave more offspring in the next generation can increase the altruist's genetic contribution to the next generation. This benefit must evaluated relative to the cost incurred by the altruist.
b) reciprocity- unrelated individuals should help each other if they can expect to get help in the future. This requires that the individuals can recognize each other, and are likely to interact more than once. Individuals that cheat (don’t reciprocate) should not be helped in the future. The tit-for-tat strategy accomplishes this.
c) group selection- may facilitate the evolution of altruism in subdivided populations. Suppose a population of birds consists of 25 altruists that make alarm calls, and 25 selfish birds that do not call. They forage in groups of 10 birds. Within each group, altruists have a higher risk of predation because they are conspicuous when they call. But groups that consist of more altruists suffer less mortality overall because the whole group is more likely to detect and escape predators. When the groups rejoin during the breeding season, there will be more surviving altruists than selfish birds.
2. In some bird species, individuals born the previous year (or even earlier) remain at the nest to help their parents raise this year's batch of young. Provide some possible explanations for this cooperative behavior in which offspring initially forego attempts at their own reproduction to help raise their siblings. Try to express your answers in the context of a cost-benefit analysis.
Possible benefits of helping raise siblings: i) helper increases inclusive fitness because helper shares .5 of its genes with its sibs (assuming full sibs). This happens to be identical to the direct fitness the helper would gain by raising its own offspring. If the helpers are young and inexperienced, they can also benefit by learning how to raise offspring, so they will be more successful raising their own offspring in the future (notice that this benefit does not require kin selection -- the individual is benefiting directly).
3. Why might ritualized conflict behaviors, like growls and aggressive/submissive posture have evolved?
By ritualizing conflict behaviors, animals can assess who is stronger (more dominant) and likely to win a fight. Thus, they can both can avoid injury or even death
4. What are some of the possible costs and benefits to living in a group?
Costs: attract predators; increased competition; increased risk of disease transmission. Benefits: possible benefits from altruism (reciprocity); added protection from predators (via mobbing behavior, scanning, alarm calls, swamping effects); easier to find mates; groups may capture or find food more easily.
5. For the following hypothetical organisms, please indicate whether you'd expect the male or female to exhibit more mate choice (i.e., which should be "choosier"), and whether you'd expect the male or female to be more brightly colored or adorned with "advertisements". Please also explain your rationale.
a. A male builds a nest and then guards the developing eggs from predators. The eggs develop rapidly and the male is able to raise many broods in a single reproductive season.
b. A male builds a nest and guards the eggs from predators. The nest is small and can hold only a single clutch. Males cannot raise more than one brood, although females can lay several clutches of eggs in a single season.
c. Fertilization is external. Females require great quantities of energy to make eggs than males require to make sperm.
d. Fertilization is internal and development is viviparous (within the female). Brood size is very small (one or two young) and gestation time is long.
a. male is limited by access to females, therefore males should advertise and females should be choosy. b. females are limited by males, so females advertise and males are choosy c. females make greater contribution than males, so females are choosy and males advertise d. again, females choosy, males advertise
6. Behavioral ecologist often rely on optimization models. Explain their rationale is using this approach. Do scientists believe that organisms are perfect machines that are fine tuned to their environment (e.g., the organisms' behavior and morphology are "optimal")? Why is/isn't this the case?
Behavioral ecologists use optimization models to evaluate and find solutions to complex problems, that often involve trade-offs and constraits. Animals have limited time and energy to devote to activities . The underlying assumption of Opt. Models is that the "best strategy" maximizes fitness. These strategies are compromises among devoting time to different activities such as scanning for predators, looking for food, etc. NO- scientists do not believe animals are perfect- there could be several different strategies that result in similar fitness. Or, the environment is complex and variable, so the "best" strategy is always changing. Or, it may not be possible to attain the "best " strategy. In general, behavioral ecologists often consider Optimization models as "yardsticks" by which to judge the actual behavior of animals. They also use the models as a way to formulate hypotheses and generate tests of these hypotheses.
7. In optimal foraging models, a number of trade-offs and costs and benefits are assumed. Give some examples.
Time constraints -- can't be in two places at one time, or engage
in two activities, such as searching and handling, or feeding and courting
and predator avoidance.
Trade-offs -- such as the best feeding locations being the riskiest; the
most energetically rich foods being harder to capture.