Species can live in the same habitat without constantly competing because they often use different resources, occupy different parts of the environment, or need those resources at different times. Even when two species depend on some of the same food, water, space, or shelter, differences in how they use those resources can reduce direct competition.
This separation is called resource partitioning. It allows species with overlapping needs to coexist rather than one species completely excluding the other.
Species do not use a habitat in exactly the same way
A habitat contains many resources and conditions, but species rarely use all of them in the same way. Two animals living in the same forest, for example, may eat different foods, search for food in different places, or be active at different times.
One species might feed mainly on insects on tree trunks while another catches insects among leaves. Both depend on insects, but they are not using exactly the same part of the available food supply.
Plants can also divide resources. Different plant species may have roots at different depths, allowing them to obtain water and minerals from different layers of soil. Their leaves may also occupy different positions in the vegetation, giving them different amounts of light.
These differences can make the same habitat large enough, in ecological terms, to support several species.
Resource partitioning reduces direct competition
Competition occurs when organisms need the same limited resource. The more closely two species overlap in their use of a scarce resource, the greater the potential for competition.
Resource partitioning reduces that overlap. Species may differ in three major ways: what they use, where they use it, and when they use it.
A useful way to think about these differences is:
- Different resources: Two species eat different foods.
- Different places: They use different parts of the same habitat.
- Different times: They use the same resource at different times.
These divisions do not have to be absolute. Species can still overlap considerably while avoiding enough competition to coexist.
The same food does not always mean the same competition
Two species can eat similar foods without competing equally for every item.
Suppose several bird species feed on insects in the same tree. One may specialize in insects on outer branches, another may search among leaves, and another may feed closer to the trunk. Their diets may overlap, but their feeding locations and behaviors differ.
Competition becomes especially important when a resource becomes scarce. If food is abundant, several species may be able to use it with little conflict. When the same food becomes limited, however, differences in feeding behavior or habitat use can become much more important.
This is one reason coexistence can change when environmental conditions change.
Species can divide space within the same habitat
A habitat is not uniform. A forest contains tree canopies, trunks, branches, understory vegetation, leaf litter, soil, and other distinct environments. A pond has open water, shallow edges, submerged vegetation, and sediments at the bottom.
Different species can specialize in different parts of this three-dimensional environment.
Two species may therefore be neighbors without using the same physical space in the same way. One may live mainly in the canopy while another stays near the ground. Both occupy the same forest, but their day-to-day interactions with the environment are different.
This spatial separation can reduce encounters and competition.
Timing can separate species that need the same resources
Species can also divide resources by time.
Some animals are active mainly during the day, while others are active at night. Two species might use similar food resources but encounter less competition because they search for them at different times.
Seasonal differences can have a similar effect. One species may make greater use of a resource during one part of the year, while another relies on it more during a different period.
Time-based separation does not eliminate competition completely, but it can reduce how much the resource needs of two species overlap at any particular moment.
Different adaptations make coexistence possible
Species sharing a habitat often have traits that fit different ecological roles. These traits can involve body size, feeding structures, rooting depth, behavior, activity patterns, or tolerance of particular environmental conditions.
For example, differences in body size can affect which foods an animal can efficiently obtain or which parts of a habitat it can use. Differences in feeding structures can allow related species to exploit different types or sizes of food.
Over many generations, natural selection can favor traits that help organisms use available resources effectively. The result can be ecological differences between species that live in the same environment.
Competition can still happen
Resource partitioning does not mean species never compete.
If two species require the same limited resource in the same place and at the same time, competition can be strong. One species may gain an advantage and reduce the other species’ access to the resource.
In ecology, the important point is that coexistence requires enough separation in resource use for competition not to prevent both populations from persisting.
Species can therefore share a habitat while competing over some resources and avoiding strong competition over others.
Predators and other interactions also shape coexistence
Competition is only one part of how species interact.
Predators can influence which species are able to persist in a habitat, while herbivores can affect plant communities. Species may also provide benefits to one another through interactions such as pollination or seed dispersal.
These interactions can change the balance among competing species. As a result, whether two species coexist is usually determined by several ecological relationships rather than by competition alone.
Coexistence depends on the environment
The way species divide resources is not fixed under every condition. Changes in temperature, rainfall, food availability, vegetation, predators, or other environmental factors can alter which resources are available and how strongly species compete.
A difference that is sufficient for coexistence under one set of conditions may become less important when the environment changes.
The key to coexistence is therefore not that species completely avoid one another. It is that their ecological needs and resource use are different enough that they can persist in the same habitat without one consistently preventing the other from obtaining what it needs.
