Limiting Factors
Populations are influenced by the resources and environmental conditions around them. A limiting factor is anything that restricts population growth, population size, or where a population can live.
What Is a Limiting Factor?
Every population exists within an environment that has limits. Organisms need resources and suitable environmental conditions, and those resources or conditions may prevent a population from continuing to increase.
Limiting factors can be living or nonliving. They can also affect populations differently depending on the environment.
Density-Dependent Factors
When more individuals live in the same area, they are more likely to interact with one another. This can increase competition, disease transmission, and predation.
Competition
More individuals may compete for limited food, water, territory, or other resources.
Disease
Disease can spread more easily when individuals live close together.
Predation
Predators may encounter prey more frequently when prey populations are dense.
Parasitism
Parasites can spread more easily when hosts occur at higher densities.
Density-Independent Factors
These factors are often associated with physical or environmental events. Their effects do not depend on how crowded the population is.
Drought
Reduced precipitation can decrease water availability and plant growth.
Flooding
Floods can alter habitats and cause direct mortality.
Fire
Wildfires can rapidly change habitat conditions and remove vegetation.
Extreme Temperatures
Temperature extremes can make conditions unsuitable for survival.
Common Limiting Factors
| Limiting Factor | Possible Effect on a Population |
|---|---|
| Food | Less available food can reduce survival and reproduction. |
| Water | Limited water can restrict survival and population growth. |
| Space | Limited space can increase competition for territory and resources. |
| Predation | Predators can reduce prey population size. |
| Disease | Disease can increase mortality and reduce population growth. |
| Temperature | Temperatures outside an organism's tolerance range can reduce survival. |
| Natural disasters | Events such as fires, floods, or storms can rapidly reduce populations. |
Limiting Factors and Carrying Capacity
Limiting factors are closely connected to carrying capacity.
For example, if food is scarce, food availability may limit population growth. If food becomes more abundant, another factor such as water or space may become the factor that most strongly restricts population growth.
Putting It Together
A deer population begins increasing because food is abundant. As more deer occupy the area, competition for food and space increases. Disease may also spread more easily among the crowded deer.
In this situation, food availability, space, competition, and disease can all act as limiting factors. Together, these factors help determine the population size the environment can support.
One Factor Can Change the Importance of Another
Limiting factors do not always operate independently. A change in one environmental condition can affect other factors.
For example, a drought can reduce plant growth. Reduced plant growth means less food is available to herbivores. The reduced food supply can then affect the population size of those herbivores.
Common Misconceptions
A limiting factor can affect population growth without directly causing death. For example, limited food may reduce reproduction.
Both biotic and abiotic factors can limit populations. Competition, predation, and disease are examples of biotic limiting factors.
Some limiting factors depend on population density, while others can affect populations regardless of their density.
If You See This on a Test...
If its effect becomes stronger as population density increases, think density-dependent. If it affects populations regardless of density, think density-independent.
Quick Practice
- What is a limiting factor?
- What is the difference between density-dependent and density-independent limiting factors?
- Is competition density-dependent or density-independent? Explain.
- Is a drought generally density-dependent or density-independent?
- How can limiting factors affect carrying capacity?
- Give one example of a biotic limiting factor and one example of an abiotic limiting factor.
Key Takeaways
- Limiting factors restrict population growth, size, distribution, or abundance.
- Limiting factors can be biotic or abiotic.
- Density-dependent factors become more influential as population density increases.
- Density-independent factors affect populations regardless of population density.
- Limiting factors help determine an environment's carrying capacity.
- Changes in environmental conditions can change which factors are most limiting.
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