What does it mean to compete?
If you are in competition with someone, it usually means you are in a contest for a prize. The prize might just be bragging rights. In nature, the stakes are higher. Organisms must compete for resources necessary for life.
Recall that ecology is the study of how living organisms interact with each other and with their environment. But how do organisms interact with each other? Organisms interact with each other through various mechanisms, one of which is competition. Competition occurs when organisms strive for limited resources. Competition can be for food, water, light, or space. This interaction can be between organisms of the same species (intraspecific) or between organisms of different species (interspecific).
Intraspecific competition happens when members of the same species compete for the same resources. For example, two trees may grow close together and compete for light. One may out-compete the other by growing taller to get more available light. As members of the same species are usually genetically different, they have different characteristics, and in this example, one tree grows taller than the other. The organism that is better adapted to that environment is better able to survive. The other organism may not survive. In this example, it is the taller tree that is better adapted to the environment.
Interspecific competition happens when individuals of different species strive for a limited resource in the same area. Since any two species have different traits, one species will be able to out-compete the other. One species will be better adapted to its environment, and essentially "win" the competition. The other species will have lower reproductive success and lower population growth, resulting in a lower survival rate. For example, cheetahs and lions feed on similar prey. If prey is limited, then lions may catch more prey than cheetahs. This will force the cheetahs to either leave the area or suffer a decrease in population.
Looking at different types of competition, ecologists developed the competitive exclusion principle. The principle states that species less suited to compete for resources will either adapt, move from the area, or die out. In order for two species within the same area to coexist, they may adapt by developing different specializations. This is known as character displacement. An example of character displacement is when different birds adapt to eating different types of food. They can develop different types of bills, like Darwin’s Finches (Figure below). Therefore, competition for resources within and between species plays an important role in evolution through natural selection.
An example of character displacement, showing different types of bill for eating different types of foods, in Darwin’s or Galapagos Finches.
character displacement: The development of different specializations so that two species within the same area can coexist without competition.
competition: Relationship between organisms when they strive for limited resources.
competitive exclusion principle: States that when two species compete, the species less suited to compete for resources will either adapt, move from the area, or die out.
ecology: The study of how living organisms interact with each other and with their environment.
evolution: The change in the characteristics of organisms over time; the change in species over time.
intraspecific competition: Relationship between organisms of the same species that strive for limited resources.
interspecific competition: Relationship between organisms of different species that strive for limited resources.
natural selection: Causes beneficial heritable traits to become more common in a population, and unfavorable heritable traits become less common.
- Competition, or when organisms strive for limited resources, can be between organisms of the same species (intraspecific) or organisms of different species (interspecific).
- In order for two species within the same area to coexist, they may develop different specializations; this is known as character displacement.
Use the resource below to answer the questions that follow.
Anemones Attack at Shape of Life http://shapeoflife.org/video/behavior/cnidarians-anemones-fight (2:49)
- What sort of competition are these anemones displaying?
- Looking at the size of the sea anemones in this video, are you surprised by the amount of space they they feel they need? Explain your thinking fully.
- What must be true about the energetic costs of anemone fighting versus the energetic gains? What would happen to the population if this were not the case?
- Notice in in the video that some individual anemones are closer to their neighbors than are the fighting anemones. Scientists have determined this situation can arise when the adjacent anemones arise from asexual reproduction and are thus related. Does knowing that sea anemones can detect "relatives" and not fight with them affect your view of what the sea anemones gain through fighting?
- What is the difference between intraspecific and interspecific competition?
- How can competition contribute to evolution through natural selection?
- What has to be true about available resources for competition to exist?