What is environmental resistance? Explain the S-shaped growth curve of a population with a sketch.

1. 1 · Define. Environmental resistance is the set of physical and biological factors that stop a species from breeding at its maximum rate.
2. 2 · Lag phase. A few organisms settle in a new area; growth is slow.
3. 3 · Growth phase. Plenty of food and little competition: births rise, deaths stay low, and numbers shoot up.
4. 4 · Stable phase. Food, space or disease limit numbers; births equal deaths, and the size levels off near the carrying capacity.
5. 5 · Sketch it. [Graph: number against time; S-shaped curve with lag, growth and stable phases; dashed line for carrying capacity]
6. 6 · Close in one line. So environmental resistance turns fast growth into a steady population.

Scoring tip: Label both axes and all three phases; an unlabelled curve earns little.