Module 8
1. Module 8
1.42. Page 5
Module 8—Populations, Individuals, and Gene Pools
Lesson Summary
This lesson focused on the following questions:
- What are the different types of population growth patterns?
- How do growth patterns illustrate these types of changes over time?
In this lesson you have discovered that the biotic factors affected by population density are called density-dependent factors. Examples are food, water, oxygen, space, parasitism, and predator populations. The abiotic factors that affect population density are called density-independent factors. Examples are climate, temperature, storms, drought, frost, wind, and precipitation.
You were introduced to the term biotic potential, symbolized by r, which is, given unlimited resources, the highest rate of reproduction. Populations growing at biotic potential form a J curve and have exponential growth rates, while populations growing in environments with limited resources will not exceed a population size known as the carrying capacity, symbolized by K. These populations growing in environments with limited resources will display an S-shaped or logistic growth curve.
By analyzing the parts of population graphs and their trends, scientists can explain changes in population growth, such as reasons for declining population size, and predict the future of populations and the impact their growth might have on the environment.
Lesson Glossary
Consult the glossary in the textbook for other definitions that you may need to complete your work.
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 limiting factors: biotic factors that limit a habitat’s carrying capacity (e.g., parasites, disease, increase in predators, lack of water, food, or 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: the 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: a 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
exponential phase: the second phase of a growth graph in which population size increases significantly because limiting factors are not yet significant
fecundity: the ability of an organism to be fertile or to reproduce
J curve: population growth with a brief lag phase and a steep increase in the growth curve
lag phase: the first phase of a growth graph showing little increase in population numbers
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
S curve: a logistic growth pattern with a lag phase, growth phase, and stationary phase in which limiting factors become significant
stationary phase: the third stage of a population growth graph in which population size stabilizes because of the balance between environmental resistance and biotic potential