Module 8

Module 8—Populations, Individuals, and Gene Pools

Explore

The Amazing Race

In your imagination, visualize a competition in which all species of the planet are challenged to the following two tasks to complete in order to win the competition:

• Make as many offspring as possible, but your offspring must survive long enough to reproduce.
• Spread yourselves as far and wide over the planet as possible.

Each entrant is given $1000 in ATP energy currency that can be used to complete the tasks. How each species spends the “money” is entirely up to them, but each body system employed in the quest requires more energy. The strategy used by each species to complete the tasks is called reproductive strategy.

What would go into developing a reproductive plan?

• Would the type of environment you’re in make a difference to your strategy? (stable versus unstable)
  
  
• Is it better to reproduce at biotic potential (r) or just enough to remain at carrying capacity (K)?
  
  
• Should you attempt to improve your offspring’s survival by nurturing them, or should you just concentrate on producing the maximum number of offspring?
  
  
• Should you begin reproducing as soon as possible in your life cycle, or should you wait until later, when you’re more mature?
  
  
• Is it better to reproduce only once a year, when conditions are good, or continually?

Of course you know that the strategies used by species to survive are not chosen; rather, they are the result of the organism’s environment selecting for the most suitable random mutations. The successful alleles/phenotypes become more common in the gene pool and eventually become typical of the species’ reproductive strategy. However, biologists have noticed that two major reproductive strategies have emerged: the r-selected strategy and the K-selected strategy. It is these two strategies that are the subject of this lesson.

Read

Read “Life Strategies” on pages 712 to 713, and “Sharing the Biosphere” from page 731 to the end of “Earth’s Carrying Capacity” on page 736 in the textbook. Make notes in your course folder on your readings, including examples of age pyramids.

Watch and Listen  

The video “Patterns of Population Growth and Management: Conserving Our Future” reviews many of the concepts that you have learned in this module and also the r- and K-selected strategies that you have learned in this lesson. You should concentrate on the following segments as you watch the video:

• “Population Growth Curves”
• “Bio Review: J-Shaped Growth Curve”
• “Natural Populations”
• “Bio Review: S-shaped Population Growth Curve”
• “Survivorship Curves”

Self-Check

SC 1. Complete the following table in your course folder using your reading assignment of pages 712 to 713 of the textbook.