1. Plants produce oxygen (other examples also possible)
2. Mutualism
3. Another hypothesis could make the same prediction
4.  Statistical power
5.  e.
6.  b.
7. Liebigís Law of the Minimum
8.  Plot  of survival, reproduction on vertical axis, level of abiotic factor on horizontal axis, showing bell-shaped curve that is broad.
9.  regulator
10.  e.
11. conduction
12.  convection
13.  a.
14. b.
15.

16. essential
17. specialist
18.  The conditions species can occur within are limited beyond basic requirements by biotic factors
19. b.
20.-21.
Hypothesis 1: birds benefit from grouping where hawks are present because each individual can spend less time being vigilant and therefore forage more
Hypothesis  2: selfish herd effect: birds benefit from grouping where hawks are present because each is less likely to be taken by a predator, since in a group thereís a higher chance that a predator will take someone else
22. polygyny
23. c.
24.  a.

ESSAY:
 
25. The large sample size (40 from one area, 55 from the other) decreases random error and makes it likely that a trend will be found if one is present, thus avoiding the possible error of concluding no trend is present when one really is.  Randomly selecting locations from which to sample decreases systematic error and avoids the errors of either creating a trend that is not real through systematic error or hiding a real trend through systematic error.  Replication is inadequate; since only one of each type of site was sampled, it is possible that it is not the presence of the other seahorse species but rather some other factor that led to the significant difference in reproduction between the areas.

26. Hypothesis 1: helpers do not breed because there are not enough mates available for them
Hypothesis 2: helpers do not breed because breeding habitat is limited since it requires the tunnel system

To distinguish between these hypotheses, dig artificial tunnel systems in some areas of suitable habitat and compare these to control areas of suitable mongoose habitat without artificial tunnels.  Hypothesis 2 predicts that non-breeders will begin breeding in the artificial tunnel systems; Hypothesis 1 predicts that they will not.

Hypothesis to explain why non-dispersers act as helpers: one of the following: increase chance of inheriting breeding territory, improve subsequent reproduction by obtaining experience rearing young.
 
27. Adaptation to different temperatures means the different populations have evolved genetic differences in ability to tolerate temperatures.  Acclimation to different temperatures means that individuals adjust physiologically to temperatures once they have experienced them for some period of time.  To test for acclimation, keep salamanders from both populations in lab, with one set of indivs from both pops in warm conditions, one set in cold conditions.  After several weeks, test swimming speed (or some other measure of physical or enzyme performance).  The acclimation hypothesis predicts that salamanders of both pops that have been kept in warm conditions will perform better in warm conditions, while salamanders of both pops that have been kept in cold conditions will perform better in cold conditions.
 
28. The wolf should require the least energy per gram and the otter the most.  Wolves are larger, and as size increases, surface area per volume decreases because surface area increases in proportion to the square of the radius and volume increases as the cube of the radius, so volume gets larger faster than does surface area.  Since heat is stored in the volume of an animal but gained or lost across the surface, the smaller the SA/V, the more heat is stored compared to heat lost, and the less energy has to be spent maintaining a warm body.  The otter requires more energy than does the raccoon because it is more elongate; the raccoon is more spherical. Spheres have the lowest SA/V. Since the otter is less like a sphere, it has higher SA/V and so (for the reasons described above) requires more energy to maintain a warm body.