Module 9S2 Changes in Populations

4.9.3S2 page 4

Reflect and Connect

 

Apply your skills and understanding of this lesson by completing the following assessment and submitting it to your instructor.

 

Module 9: Section 2—Lesson 3 Assignment

 

Zebra Mussels

 

Zebra mussels were introduced into the Great Lakes inadvertently from ballast from a European freighter. Since then zebra mussel populations have increased rapidly and become a major ecological problem.

 

Retrieve your copy of Module 9: Section 2—Lesson 3 Assignment that you saved to your computer earlier in this lesson. Complete the assignment. Save your completed assignment in your course folder. Submit your completed Module 9: Section 2—Lesson 3 Assignment to your teacher for assessment.

Lesson Summary

• Biotic factors that are affected by population density are called density dependent factors. Examples are food, water, oxygen, space, parasitism, and predator populations.
• Abiotic factors that affect population density are called density independent factors. Examples are climate, temperature, storms, drought, frost, wind, precipitation.
• Given unlimited resources the highest rate of reproduction is called biotic potential, symbolized by r.
• Populations growing at biotic potential form a J curve and have exponential growth rates.
• Populations growing in environments with limited resources will not exceed a population size known as the carrying capacity, symbolized by K.
• Populations growing in environments with limited resources will display and S-shaped or logistic growth curve.

Lesson Glossary

 

biotic potential (r): highest per capita growth rate possible

 

carrying capacity (K): the theoretical maximum population size that the environment can sustain over an extended period of time; may change as the quality of the habitat changes

 

The population is at carrying capacity when it levels off during logistic growth.

 

density dependent factors: biotic factors that limit a habitat’s carrying capacity (e.g. parasites, disease, increase in predators, lack of water/food/territory); the impact increases with the density of the population

 

density independent factors: abiotic factors that limit a habitat’s carrying capacity (e.g. fire, flood, frost)

 

The impact is not affected by the density of the population.

 

environmental resistance: rhe combined effects of factors that limit population growth; prevents a population from growing at its biotic potential; determines the carrying capacity of the environment

 

exponential growth pattern: exhibited by a population that doubles with each generation; results in a J-shaped curve; begins with a lag phase, followed by a steep rise

 

The term ‘exponential phase’ refers to a section of the logistic growth curve (S) where births exceed deaths. This phase occurs after the lag phase and before the stationary phase.

 

logistic growth: a population increase resulting in an S-shaped curve

 

Begins with slow growth, steepens to exponential growth, and then levels to a carrying capacity due to competition because of environmental resistance.