Carrying Capacity
Populations cannot grow indefinitely. Eventually, the resources and conditions of an environment place limits on how many individuals can be supported.
What Is Carrying Capacity?
Carrying capacity is not simply the largest number of organisms that could physically fit in an area. It depends on whether the environment can provide enough resources and suitable conditions over time.
Why Is Population Growth Limited?
Populations need resources such as food, water, shelter, space, and nutrients. When a population becomes larger, individuals may compete more intensely for those resources.
As resources become limited, birth rates may decrease and death rates may increase. Population growth therefore slows as the population approaches the environment's carrying capacity.
Imagine a population of deer living on an island. If food and water are abundant, the deer population may increase. As the population grows, however, the available vegetation may become insufficient to support additional deer. The population may then level off around the carrying capacity.
Factors That Affect Carrying Capacity
| Factor | How It Can Limit Population Size |
|---|---|
| Food | Insufficient food can reduce survival and reproduction. |
| Water | Limited water can prevent organisms from surviving or reproducing. |
| Space | Limited living space can increase competition. |
| Shelter | Insufficient shelter can increase exposure to predators or environmental conditions. |
| Disease | Higher population density can make disease transmission easier. |
| Predation | Predators can reduce the number of individuals in a population. |
Carrying Capacity on a Population Graph
Carrying capacity is often represented on a population-growth graph as a relatively stable level around which population size fluctuates.
A population does not necessarily remain exactly at the carrying capacity. It may rise above it temporarily and then fall below it as resource availability and other environmental conditions change.
Can Carrying Capacity Change?
Yes. Carrying capacity is not necessarily a permanent number.
Changes in environmental conditions can increase or decrease the number of organisms an environment can support.
If rainfall increases and plants become more abundant, an environment may temporarily support a larger population of herbivores. If a drought reduces available vegetation, the carrying capacity for those herbivores may decrease.
Carrying Capacity vs. Population Size
| Term | Meaning |
|---|---|
| Population size | The number of individuals currently in a population. |
| Carrying capacity | The population size the environment can sustainably support under particular conditions. |
Common Misconceptions
Population size can fluctuate around carrying capacity as environmental conditions change.
Changes in food, water, space, climate, predation, disease, and other factors can change carrying capacity.
Multiple limiting factors can influence how many individuals an environment can support.
If You See This on a Test...
If the question describes something that prevents a population from growing indefinitely, look for a limiting factor.
Quick Practice
- Define carrying capacity.
- Why can't most populations grow indefinitely?
- Name two resources that could limit a population.
- Can carrying capacity change over time? Explain.
- What would likely happen to a population if its food supply suddenly decreased?
Key Takeaways
- Carrying capacity is the maximum population size an environment can sustainably support under particular conditions.
- Limited resources prevent populations from growing indefinitely.
- Food, water, space, shelter, disease, predation, and other factors can affect carrying capacity.
- Carrying capacity can change when environmental conditions change.
- Population size may fluctuate around carrying capacity rather than remaining exactly constant.
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