Population Growth and Resource Availability
Introduced| English | Meaning |
|---|---|
| limiting factor/ˈlɪmɪtɪŋ ˈfæktə/ | A factor whose availability restricts the rate or extent of a process. |
Growth depends on resources
- How fast a population grows depends on what is available.
- With plenty of food and space, numbers explode.
- When resources run short, growth slows to a halt.
- Two curves describe these two situations.
Exponential growth: the J-curve
- With unlimited resources, a population grows exponentially.
- Each generation adds more individuals than the last.
- Plotted over time, this makes a J-shaped curve that steepens.
- But no real environment offers unlimited resources for long.
A deer herd: when a population approaches carrying capacity, resources limit further growth
With unlimited resources, a population grows…
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With no limits, growth is exponential — a J-shaped curve that gets ever steeper.
Logistic growth: the S-curve
- As resources run short, growth slows.
- This turns the J-curve into a logistic S-curve.
- The population levels off at the carrying capacity, K.
- Real populations usually follow this S-shaped pattern.
Exponential then logistic growth
J-curve, then S-curve at K
With unlimited resources growth is exponential (J); with limits it becomes logistic (S), leveling at K.
When resources become limited, growth becomes…
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Limited resources turn exponential growth into logistic growth, which levels off at K.
Anything that slows population growth, like scarce food, is a ____ factor.
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A limiting factor (food, water, space, disease) restricts how large a population can grow.
Limiting factors
- A limiting factor 限制因素 is anything that slows or caps growth.
- Food, water, space, and disease are common limiting factors.
- More resources raise the carrying capacity, allowing a larger population.
- Fewer resources lower it, forcing the population down.
A population keeps growing forever when resources are abundant.
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False. More resources raise the carrying capacity, but growth still levels off once the population reaches that new limit.
Select all true statements about population growth.
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Real growth cannot stay exponential forever — resources run out. The other three are correct.
Exponential (J-curve) growth cannot last. It looks unstoppable, but every environment has limits. Sooner or later a limiting factor — food, space, disease — slows the growth into a logistic S-curve. A J always bends into an S in the real world.
Bacteria in fresh nutrients:
- Drop bacteria into a dish full of food: they grow exponentially, a steep J-curve.
- As the food runs low and waste builds up, growth slows.
- The population levels off at the carrying capacity — the J-curve has become an S-curve, limited by resources.
Population growth depends on resources. With unlimited resources, growth is exponential (a J-curve); with limits, it becomes logistic (an S-curve) that levels off at the carrying capacity. A limiting factor — food, water, space, disease — slows growth, and more resources allow a larger population.