Population Growth and Resource Availability
Introduced| English |
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| limiting factor/ˈlɪmɪtɪŋ ˈfæktə/ |
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.
With unlimited resources, a population grows…
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…
Limited resources turn exponential growth into logistic growth, which levels off at K.
Anything that slows population growth, like scarce food, is a ____ factor.
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.
More available resources generally allow a population to grow larger.
Abundant resources raise the carrying capacity, letting the population grow larger before leveling off.
Select all true statements about population growth.
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.