Competition occurs when species overlap in their use of limiting resources, either through interference or exploitation. At one extreme, if a superior competitor prevents another species from using essential resources, the inferior species may be competitively excluded. In reality, most species show competitive coexistence, which is maintained through a variety of ecological processes, including resource partitioning, environmental conditions, disturbance, and predation. The distribution of a species may be affected by competition when another species restricts the use of limiting resources to a particular location.
learning outcomes
You should be able to:
Contrast the concepts of fundamental niche and realized niche, and distinguish each with examples.
Distinguish between interference competition and exploitation competition, and give examples of each.
Describe how both competitive exclusion and competitive coexistence affect interspecific competition and the population growth of interacting species.
The fundamental niche of the native Eurasian red squirrel includes all of the United Kingdom. Since the introduction of the eastern gray squirrel, a non-
A realized niche is defined by a species’ interactions with other species. The red squirrel’s realized niche has become smaller because of the competition with the gray squirrel.
Refer to Question 3 in the Key Concept 55.2 recap. What species interaction controls the coexistence of competing grass species? Explain how this interaction can promote species diversity.
Herbivory by the hares is the interaction that allows the grass species to coexist with one another. By grazing on the dominant grass species, the hares allow more subordinate grass species to thrive.
Suppose you are sharing a milkshake with a friend. You each have a straw. Under scenario 1, you both drink from your straws, eventually consuming the entire milkshake together. Under scenario 2, your friend takes both straws and drinks the whole milkshake. Which scenario is an example of interference competition and which is an example of exploitation competition?
Scenario 1 is an example of exploitation competition because you and your friend are sharing the milkshake resource. Scenario 2 is an example of interference competition because your friend is excluding you from the milkshake resource
Prior to the 1990s, most ecologists believed that positive interactions were interesting, unusual phenomena, but of limited importance to populations and communities. Most of their focus was on the role of negative interactions such as predation and competition. But research over the last few decades shows that just like negative interactions, positive interactions can have important consequences for the growth, reproduction, and survival of species, especially under stressful conditions. Let’s turn our attention to how positive interactions might promote the coexistence of species.