B140 Behavioral Ecology Fall 2004 Midterm Key

**Calculate your final percentage= (points received/120)x107.9**

1. Explain the basic premises of the ideal free distribution. Are there any animals that exhibit the ideal free distribution? (Why or why not?)

10 pts: The ideal free distribution assumes that animals have information on resource distribution in their environments and distribute themselves to match them.

5 pts: Some animals are close to ideal free distribution, but are cognitively constrained. It is easier to see an absolute difference in resources than a relative difference, so they try to distribute to the best of their abilities.

5 pts: The ideal despotic distribution can interfere. More aggressive dominant animals can monopolize the best patches and/or force less aggressive ones into less favorable patches.

 
 
 
 
 
 
2. Draw a graphical model that explains why reef fish should transform from male to female.
 

Female fitness ~ size because of fecundity selection. (2) Male fitness does not ~ size because he is a sneaker or due to scramble competition. (2)

3. In the t-allele example, how is the force of genic selection balanced by the process of individual selection? How does the process of group selection favor non-t-allele mice?

5 pts: The t-allele provides an example of genic selection because it increases faster than the wild-type allele in the population (due to segregation distortion in sperm)

5 pts: Individual selection balances this because homozygotes for the t-allele are sterile. Thus, at the level of the individual, the t-allele is negatively related to fitness.

10 pts: Group selection favors the non-t-allele by the extinction of groups that become fixed for the t-allele and survival of groups that have not become fixed at the t-allele locus.

 

 

 

 

 

4.  Why might animals appear to be risk aversive? Explain in terms of a bumblebee foraging on flowers and a cognitive model of memory.

8 pts: Animals appear risk aversive due to cognitive constraints.

8 pts: If they base foraging decisions off of limited memory and their most recent visits to variable yield flowers have been worthless (calculated gains will be much lower than constant flowers), they will avoid risks until energy reserves are too low.

4 pts: This causes memory capacity to expand.

 

5. 2. How are badges used in male contest? What are the advantages to a the badge holder? How are badges used in female choice? What are the advantages to a choosy female? How are such badges costly? Note: an answer spanning three lectures.

4pts. Badges are used to convey information about RHP (physical strength) in asymmetric contests.

4pts. The badge holder can avoid many contests with physically inferior males (saving energy and time)[Incidentally the receiver male also benefits from the information by not engaging in a fruitless fight].

 

4pts. Badges can also be used like other indicator traits allowing the female to gain information about a males overall vigor (e.g., there could be variation in males with or without the badge).

4pts. Females gain an indirect benefit by choosing well-endowed males (e.g., with respect to the badge) and thereby pass on potential good genes to progeny.

4pts. Basically a physiological cost was expected. E.g., High T required to produce a badge results in lower survivorship (unless perhaps the male has lots of good genes!). [Note: There are other costs, but this is the key cost that keeps badges honest indicators!]

 

 

 

6. What are two assumptions of the model of runaway sexual selection? What is the key prediction of the theory of sexual selection by runaway process? Describe evidence supporting the key prediction. How do these two assumptions differ from indicator models of female choice?

5pts: Runaway assumes that females preference is genetically based. The male trait is also genetically based.

5pts: Given that this is true the males with elaborate traits are chosen by choosy females and female choosiness and the elaborate trait become genetically correlated in subsequent generations.

5pts: A breeding study reveals evidence of this correlation. Daughters from the same sire show choosiness and their brothers show the elaborate trait. Thus, we infer that the genes for choosiness and the elaborate male trait were both passed on from the father.

5pts: Indicator models do not rely on the elaborate male trait being due to genetic differences in trait size. The size of the male trait could be a physiological indicator of the males vigor, he can grow a large tail because he has lots of resources. Variation in the indicator trait does not have to be genetic, it just should indicate the males physiological vigor or other measure of male quality.

[NOTE: The variation arises from an interaction between Genes for the male trait and the environment or by epistatic interactions with lots of other genes. <- not strictly necessary]