Lesson 4.9.4S2

4.9.4S2 page 4

Going Beyond

Discuss the ramifications of your conclusions. How can we apply this information in the real world, where human population growth is a pressing issue?

 

Self-Check 1

Life Strategies and Population Change

Where on the population growth curve does natural selection begin to favor those with superior alleles? There are no winners without a competition. Competition only begins when scarcity of resources, waste accumulation, contagious disease, high predation and other density dependent factors become a daily fact of life. The organism’s physical, chemical, and behavioral traits combine to keep it alive and reproducing when those around it are not.

Using the following graph illustrating exponential and logistic growth, answer the questions and file your work in your course folder.

Logistic (S) versus Exponential (J) growth curves

 

 

SC 1. Label the region on the logistic curve where you would expect there to be the greatest competition and therefore selection of favorable alleles. Support your answer.

 

SC 2. Label the region on the logistic graph where you would expect to see the highest concentration of ‘winners’ (those with the most favorable alleles). Support your answer.

 

Sc 3. Where on this graph would you expect to see the predator-prey cycles that we discussed in a previous lesson occurring? Support your answer.

 

SC 4. What would you expect to happen to the J curve if it were extended? Why?

 

Check your work.

 

Self-Check

Application of Growth Curves to Different Species

For wildlife managers, deviations from expected growth patterns indicate a problem.

 

SC 5. In lesson 3, Try This, you graphed the data from a population of caribou from 1910 to 1950 that showed an extended period of exponential growth followed by a crash. Considering what you know now about the characteristics of K-selected species, was the graph typical? Why or why not?

 

SC 6. According to the table you created in Assignment #1 above, are Homo sapiens r or K selected? View figure 20.22 on page 733. Does the population growth curve support your decision? Why or why not?

 

SC 7. Read p.733 and 735 and view the Age Pyramids in Figure 20.23 to see age-pyramid representations of growth rates in the Congo, Sweden, and Germany. Which of the countries shows exponential growth? Negative growth? Stationary or carrying capacity growth?

 

SC 8. Compare Fig. 20.22 and 20.24. Both show human growth rates. Why does figure 20.24 appear to have a much flatter slope?

 

Self-Check Answers

SC 5. No, caribou are K-selected (large, long life spans, nurture their young) and should show an S population growth curve. There should be a short period of exponential growth that flattens out due to environmental resistance, followed by a relatively stable carrying capacity population.

 

SC 6. Homo sapiens are K selected by definition, but our growth curve shows extended exponential growth typical of r-selected species. The best explanation is that technology has raised the carrying capacity of the environment to extend the period of exponential growth. There is evidence that in recent years the slope of the curve is starting to flatten somewhat.

 

SC 7. Congo, Germany, Sweden

 

SC 8. The time axis is very compressed on the first graph so the slope is steeper. The first graph does not show future dates or computer projections of population changes.

 

Search the internet for a world population Clock. View a couple of the results to get an idea of how fast Earth’s human population is changing. Next, view Fig 20.24 on page 736 and Read p. 736. Using growth rates, age structures, environmental state, and possible technologies, population scientists have predicted the three possible scenarios you see in Fig 20.24. According to the reading, the earth’s carrying capacity will level out somewhere around __ billion. By 2060, the estimated high, medium, and low projections are respectively: ________, ________, and ______ billion.

 

Considering that the current population is over 7 billion, discuss with your teacher and classmates what each of these 3 scenarios would mean for human society. (Remember that a change in growth rate can be caused by a change in one or both of birth rate and death rate) File your comments in your course folder.