Summary
A population is a group of organisms of one species living in the same area at the same time. A community includes all the populations of different species in an ecosystem. An ecosystem is a unit containing the community of organisms and their environment interacting together. Example: A decomposing log or a lake.
- Food supply — availability of food affects population growth. Example: Abundant food can lead to rapid population increase.
- Predation — predators can control the population size of prey. Example: More predators can decrease prey population.
- Disease — diseases can limit population growth by increasing death rates. Example: An outbreak can reduce a population significantly.
- Lag phase — initial slow growth as organisms adapt to the environment. Example: Few organisms, so reproduction is slow.
- Log phase — rapid growth due to abundant resources. Example: High birth rate and low death rate.
- Stationary phase — population stabilizes as resources become limited. Example: Birth rate equals death rate.
- Death phase — population declines due to resource depletion or waste accumulation. Example: Death rate exceeds birth rate.
Exam Tips
Key Definitions to Remember
- Population: A group of organisms of one species living in the same area at the same time.
- Community: All the populations of different species in an ecosystem.
- Ecosystem: A unit containing the community of organisms and their environment interacting together.
Common Confusions
- Confusing community with population.
- Misunderstanding the phases of the sigmoid growth curve.
Typical Exam Questions
- What factors affect population growth? Food supply, predation, and disease.
- Describe the sigmoid growth curve phases. Lag, log, stationary, and death phases.
- How does disease affect population size? Increases death rate, reducing population.
What Examiners Usually Test
- Understanding of population growth factors.
- Ability to interpret population growth graphs.
- Explanation of the sigmoid growth curve phases.