Question

You are studying a population of yellow-toed cave salamanders and have described the relationship between per-capita birth and death rates as a function of density.

http://tinypic.com/view.php?pic=2afjrcw&s=9

1) list the equilibria (at which density or densities do equilibria occur?)-- ignore the "trivial" one at N=0

A) at 50, and 100

b) at 50

c) at 80

d) at 20, and 80

e) at 100

2)http://tinypic.com/view.php?pic=29zoaht&s=9#.WCn0PYWcFpg

3)http://tinypic.com/view.php?pic=2e1zy84&s=9#.WCn0hYWcFpg

Answer 1

Please find the answers and reasons below:

Part 1: For the image of the population growth, it can be seen that a state of equilibrium or equal rates of deaths and births is achieved twice where the red and green lines intersect each other, i.e. at density 20 and 80. This gives that option d is correct.

Part 2: Based upon the data for image 1, it can be suggested that the population growth increases at first until it reaches a maxima at density neary 50 and declines thenafter. Thus from the image of trajectories, it seems that option C is most correct since it gives a trend of gradual increase of population desnity by 50.

Part 3: Based upon the data for image 1, it can be deciphered that the population density gradually decreases after 80 till minima. This information is directly given by the trend shown in graph C. Hence, option C is correct.