8.3 Population Ecology

Two growth patterns

Exponential growth occurs when resources are unlimited, producing a J-shaped curve. In reality, resources run short, so growth follows logistic growth, an S-shaped curve that levels off at the carrying capacity (K) — the maximum population the environment can support.

Life strategies

As a population nears K, growth slows because of limiting factors (food, space, competition). Species differ in strategy: r-selected species produce many offspring with little care (fast growth), while K-selected species produce few offspring with lots of care (stable near K).

Key terms

Exponential growth (J-curve)

Rapid growth with unlimited resources, producing a J-shaped curve.

Logistic growth (S-curve)

Growth that slows and levels off at carrying capacity (S-shaped).

Carrying capacity (K)

The maximum population an environment can sustainably support.

Limiting factor

A resource (food, space, water) that restricts population growth.

r vs. K selection

r-selected: many offspring, little care; K-selected: few offspring, much care.

Try an AP-style question

What is the per capita growth rate (r) for the year?

1. 0.2
2. 0.5
3. 0.1
4. 50