Lesson 23 — Activity 2: Limiting Factors
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Lesson 23 — Activity 2: Limiting Factors
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What if organisms did not die? Populations would then continue to increase. Organisms, however, do die for many different reasons. You will learn about some of these reasons in this activity.
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What limits the growth of a population? Several factors in the physical environment can limit the size of a population by reducing birth rates and increasing death rates.
These include:
- water — something all organisms need
- matter — a poor supply of matter (soil) can slow the growth of plants
- weather — extreme heat or cold or drought or too much rain
These factors are called abiotic limiting factors.
What abiotic factors do you see in the above images?
There are also other factors that affect the sizes of populations. These are called biotic limiting factors.
Biotic limiting factors are ways that interactions among organisms may affect the size of a population. These factors also help control the populations in an ecosystem.
These factors include:
Competition
Competition occurs when individuals compete for nutrients (plants), food (animals), water, light, and shelter. Animals compete with each other in their own species. For example, each mountain sheep has the same needs as other mountain sheep in the population. They compete for food, shelter, and mates. The stronger mountain sheep may get the best food, while the weaker sheep may not get enough.
Individuals from different species also compete for resources. For example, rabbits eat the same food as deer.
Predation
A predator is an animal that catches and kills and then eats another animal. For example, mountain sheep's predators include coyotes, bobcats, and eagles. The relationship between predator and victim (called the prey) is called predation. Predation can benefit both predator and prey. Predators are able to acquire food, and since predators usually eat sick or weak prey, this leaves more food for the prey population.
Parasitism
Parasites are organisms that live in or on another living organism. For example, ticks are common parasites that live on deer (called hosts). The relationship between the parasites and the host is called parasitism. External parasites eat the hair, skin, or scales of the host or suck the host's blood. Internal parasites live inside the tissues of the host. Most parasites do not kill their hosts, but they do weaken them.
