Population Ecology and Community Ecology

Module 5 (9/29–10/5) · Population Ecology and Community Ecology · Blueprint Pillar 3 · PGCC Outcome 2 · Download .docx

Objectives

Describe the factors that control population growth.
Distinguish exponential growth from logistic growth.
Identify r-selected and K-selected species.
Explain mutualism, commensalism, and parasitism.

Key terms

Carrying capacity (K): Maximum population size an environment can sustain indefinitely given available resources.
Exponential growth: Population increase at a constant rate, producing a J-shaped curve — requires unlimited resources.
Logistic growth: Population increase that slows as it approaches carrying capacity, producing an S-shaped curve.
Limiting factor: Any resource or condition that restricts population growth.
r-selected species: Species with high reproductive rate, many small offspring, and little parental investment.
K-selected species: Species with low reproductive rate, few large offspring, and high parental investment.
Interspecific competition: Competition for resources between individuals of different species.
Intraspecific competition: Competition for resources among individuals of the same species.
Mutualism: Symbiotic relationship where both partners benefit (+/+). Example: bees and flowering plants.
Commensalism: Symbiotic relationship where one partner benefits and the other is unaffected (+/0).
Parasitism: Symbiotic relationship where one partner (parasite) benefits at the expense of the other (host) (+/−).
Ecological succession: The gradual process by which an ecosystem changes over time from a pioneer community to a climax community.

The concept

Population growth is driven by birth rate and immigration and reduced by death rate and emigration. Exponential growth (J-curve) occurs when resources are unlimited — population size doubles at a constant rate. Logistic growth (S-curve) is what real populations show: growth slows as density approaches the carrying capacity (K), the maximum population an environment can sustain.

Limiting factors cap growth: food, water, space, predation, and disease. Density-dependent limiting factors become more intense as population density increases. r-selected species produce many small offspring with little parental care (insects, annual plants). K-selected species produce few offspring with high parental investment (elephants, humans) and are adapted to life near carrying capacity.

Symbiotic relationships define how species interact: mutualism (+/+) benefits both, commensalism (+/0) benefits one while leaving the other unaffected, and parasitism (+/−) benefits one at the expense of the other. Ecological succession progresses from pioneer communities on bare substrate to climax communities in mature, stable ecosystems.

Self-check

Try each one before you look. A miss here costs nothing and tells you exactly what to reread.

1. Logistic growth differs from exponential growth in that logistic growth:

2. Which of the following is an example of intraspecific competition?

3. A lichen consists of a fungus and a photosynthetic alga living together. The alga provides food via photosynthesis; the fungus provides structure and moisture. This relationship is best described as:

4. The carrying capacity (K) of an environment is best defined as:

5. Primary ecological succession differs from secondary succession in that primary succession:

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