Limiting factors

By the end of this lesson, I will be able to:
By the end of this lesson, I will be able to:

A population is a group of individuals of the same species living in the same area. Some examples of populations that live in a terrestrial ecosystem are deer, wolves, ants, and maple trees. Some examples of populations that live in an aquatic ecosystem are salmon, frogs, and water lilies.
All populations have different factors affecting their growth and survival. The carrying capacity, which is the maximum number of organisms supported by the ecosystem, will depend on the availability of nutrients, habitat, water, climate, and predator-prey relationships.
The water cycle and the nitrogen cycle are two cycles involved in the Earth's systems that affect the carrying capacity and population of an ecosystem.

The Water Cycle (Hydrologic Cycle)

The Sun provides the energy that drives the water cycle. Water evaporates from the Earth's surface and returns as precipitation as it is cycled between the atmosphere and lithosphere. The availability of water is critical to the survival of all species. In deserts where precipitation amounts are low, the types of species and the carrying capacity of species are limited due to unavailability of water resources.
Humans affect the water cycle in two main ways:
withdrawing large quantities of freshwater for consumption; clearing of vegetation, reducing seepage to groundwater sources and increasing flooding risk

Nitrogen Cycle

All plants and animals require nitrogen to make proteins and nucleic acids. Although 78% of the atmosphere is nitrogen gas, plants and animals cannot use N2 in its pure form. The nitrogen must first be converted to a useable form by nitrogen fixing bacteria living within the roots of legumes and in the soil. The bacteria change the nitrogen into ammonia which is then converted to “useable” nitrates by nitrifying bacteria. Humans have had an impact on the nitrogen cycle with the industrial fixing of nitrogen for fertilizers.


A wildlife habitat is the area in which food, shelter, and space is available for an animal population. All animals and plants have different requirements for growth and reproductive success. The size and the shape of an ecosystem will limit the types of species and the size of populations it can support. In terrestrial ecosystems, some plants and animals are adapted to open areas while others are adapted to woodland interiors.


Temperature ranges and the amount of precipitation will limit the types of species capable of surviving in the ecosystem. For example, large mammals with thick fur coats are not adapted to desert-like conditions. When conditions are just right, populations may increase rapidly; such is the case with mosquito outbreaks in the spring.
In addition to precipitation and temperature, the amount of light and the strength of winds may also limit the populations of plants and animals.

Predator-Prey Relationships

Predators are perhaps one of the most important limiting factors. They are a natural control in maintaining populations. Often times the predator and prey populations will fluctuate with one another; as prey numbers decrease so too will the numbers of predators.
All species are important in ecosystems; however a keystone species plays a crucial role in maintaining the ecosystem's function by pollinating, regulating populations, and other activities. Top predators such as wolves, grizzly bears, and alligators often control prey populations.
Sea Otters in the Pacific Ocean are a keystone species as they feed on sea urchins and other shellfish thereby helping to reduce the grazing and destruction of the kelp beds, which provide habitats for many other species. In recent years many sea otters have been hunted and killed by boats and as a result these marine ecosystems have begun to change as the kelp beds are being destroyed by sea urchins.