Question

natural selection shapes different life history traits under different environmental conditions. some populations exhibit r - selection and others k - selection. compare these contrasting life histories by completing this chart
characteristic r - selection k - selection
life history emphasis 1. stability near carrying capacity
relative body size 2. 3.
number of offspring per reproduction 4. 5.
age at first reproduction younger 6.
emphasis on ___ of offspring 7. quality and care
population near k? no; resources abundant 8.
limited mostly by density - independent factors 9.
predators or pests 10. 11.
examples of organisms 12. 13.
exercise 6 (modules 36.9 - 36.11)
review the dynamics of human population growth by filling in the blanks in the following essay.
the world’s human population now totals more than 1___ billion people. we are the most numerous large animal on earth, and our huge numbers are a result of a recent burst of population growth unprecedented in the history of life.
the human population grew relatively slowly and steadily until about 1500, when there were about 2_ million people on earth. after that, population growth gradually accelerated. the population doubled to 1 billion by 1850, again to billion by 1927, and again to 4 billion by 1975. current projections suggest that the human population could reach 3_ billion by the year 2025.
population growth rate depends on two factors — per capita rate of increase, symbolized as 4_, and population size, or 5_. throughout most of human history, r was close to 6_. times were rough; although 7_ rate was relatively high, it was balanced by an ally high 8___ rate.

Explanation:

1. In r - selection, the emphasis is on high population growth rate.
2. r - selected organisms generally have smaller relative body size.
3. K - selected organisms have larger relative body size.
4. r - selected organisms produce many offspring per reproduction.
5. K - selected organisms produce few offspring per reproduction.
6. K - selected organisms have a later age at first reproduction.
7. r - selection emphasizes quantity of offspring.
8. In K - selection, the population is near the carrying capacity (Yes).
9. K - selection is limited mostly by density - dependent factors.
10. r - selected organisms may be considered pests or have many predators as they reproduce rapidly.
11. K - selected organisms are often less numerous and may be more vulnerable to predation but are not typically pests.
12. Examples of r - selected organisms include insects like flies and weeds.
13. Examples of K - selected organisms include elephants and humans.

For the human population growth part:

1. The world’s human population now totals more than 7 billion (as of common knowledge).
2. In 1500, there were about 500 million people on Earth.
3. Current projections suggest the human population could reach about 8 billion by 2025.
4. Population growth rate depends on per - capita rate of increase, symbolized as $r$.
5. And population size, or $N$.
6. Throughout most of human history, $r$ was close to zero.
7. Although the birth rate was relatively high, it was balanced by a high death rate.

Answer:

1. High population growth rate
2. Smaller
3. Larger
4. Many
5. Few
6. Older
7. Quantity
8. Yes
9. Density - dependent factors
10. Many, may be pests
11. Few, not pests
12. Flies, weeds
13. Elephants, humans
14. 7
15. 500
16. 8
17. $r$
18. $N$
19. Zero
20. Birth
21. Death