Review Questions, LIFS 101, Tuesday Aug 31, 2004

Review Q – Populationspage 1

Review questions, BIOL 101 (Dr. Scott)

Chapter 54–Population Ecology, in Purves et al. Life, 8th edition

Self quiz questions, p. 1182: 1-5.

Discussion q’s 1.

Important figures:

1. How are a biologist’s definitions of “population” and “community” different from those in everyday use?

2. To calculate population density of a species, what two variables need to be measured?

3. In an age-distribution pyramid such as Fig. 54.4, what does the width of a bar represent?

b. at what age (in this figure) does the sex ratio become noticeably “biased” in favor of females?

c. Can you think of a species in which all individuals would be of the same age? What would its age structure “pyramid” look like?

4. What are typical shapes of curves for exponential population growth, and logistic population growth? (Each is often represented as a letter of the alphabet.)

5. What variables are measured along the X and Y axes of a population growth plot?

6. Is exponential population growth possible for any (all) species? Why or why not? When and when not?

7. Is logistic population growth possible for any species? Why or why not? When and when not?

8. What population growth patterns are illustrated by (a) elephant seals on the California coast,

(b) zebra mussels in the United States and Canada,

(c) Song Sparrows on Mandarte Island, British Columbia,

(d) snowshoe hares in the Hudson Bay region?

9. If you studied a deer population in a state park for a number of years, what would be a good sign that the population was at or near its carrying capacity?

Over its carrying capacity?

10. In what units is carrying capacity measured?

11. What factors determine the carrying capacity of a population?

12. If you removed one-third of the trees in a 100-acre forest, how might that affect the forest’s carrying capacity for woodpeckers?

13. When you look at a graph of human population growth (54.20), what would you conclude about the world’s carrying capacity for humans? Have we ever shown evidence of having a carrying capacity? Has it changed?

14. From September 1 2004 to September 1 2006, the US population grew from 294,373,196 to 297,175,394 to 299,675,124.

a. What was the per capita growth rate during the first year (9/1/2004 to 9/1/2005)?

Here’s how to do it:

Per capita growth rate = net # added during year/# at beginning of year

# added = 297,175,394 – 294,373,196 = ______

Now divide by the population size on 9/1/2004.

b. What was the percentage growth rate that year?

c. What was the per capita growth rate during the second year (9/1/2005 to 9/1/2006)?

d. What was the percentage growth rate that year?

15. From September 1 2005 to September 1 2006, the world population grew from 6.466 billion to 6.542 billion.

a. Was the per capita growth rate positive, negative, or zero?

b. What was the per capita rate of growth?

16. Which of the following are true about the snowshoe hare and lynx cycles (54.11)?

a) the population of hares peaks reaches the same peak density every 8 to 11 years

b) hare population size peaks briefly (staying high for no more than 3 years) every 8 to 11 years

c) the peak in lynx population size coincides with that of hares

17. What is the dependent variable in Fig. 54.9b (Song sparrows)?

18. If there are lots of adult sparrows on the island in autumn, is the chance of a juvenile sparrow surviving high or low (relative to when there are few adult sparrows on the island)? See Fig. 54.9c

19 What did we find out about campus plants, such as Locust, Sweet Gum, in terms of their potential for population increase?

21. What sorts of simple observations prove that all species are capable of explosive population growth, at least for brief periods of time? Describe at least two kinds of observations that could be considered separate lines of evidence.

22. The equation for logistic growth of a population is dN/dt = (b – d) (N) [(K – N)/K].

a) What does this model assume (given the terms in the equation) about maximum population size and rate of growth (constant or changing?)

b) What do b, d, N, and K stand for?

c) Draw a graph of population size versus time that shows a population growing to a carrying capacity, according to the logistic equation; show the dots of population size as a continuous (possibly curving) line. Label your axes. Circle the point on the line where the rate of growth (number added per unit time) is highest.

23. The numbers below are for an imaginary population of Cardinals. The population starts with 2 pairs of adults (N =4). The net reproductive rate under ideal conditions is 1.5 cardinals added per cardinal per year (r = 1.5/yr). (I show this as r = b – d, to remind us that it’s the net reproductive rate, births minus deaths.) To show their potential for growth, imagine these are the first 4 cardinals in Indiana and there is, for a while, unlimited growth potential, as the cardinals expand throughout the state with exponential growth. See how they grow over 10 years, following the simple equation of dN/dt = rN. The females keep laying the same # of eggs, experience the same predation rate, raise a couple of broods a year maybe, and the young survive the winter at the best possible rate. See how the # added per year (dN/dt) keeps increasing.

24. Now, let’s put the 4 cardinals in a new park with a carrying capacity for cardinals of K = 200. (In the surrounding area cardinals are already at carrying capacity.) Population growth follows the logistic equation. In what year does the population first overshoot the carrying capacity? In what year is dN/dt highest?

I made these examples using formulas in an Excel spread sheet. It’s a useful exercise to play with the numbers, making (b – d) = 0.8, for example, in the examples above, or changing K from 200 to 100. And it is also instructive to graph the population size (N) versus time (year), or graph dN/dt versus time, using Excel or simply drawing a graph by hand. The logistic growth curve fits nicely on a graph page, but the exponential growth shoots up rapidly off the charts, if you stick to linear scales.