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The first species interaction we will tackle is competition, a word you are likely familiar with. But, as usual, in ecology, competition has a specific meaning. Why can't we all just get along?
Competition is the conflict between organisms for a limited essential resource.
The idea of a limited resource is key here, so don’t forget it! If resources are unlimited or plentiful, then competition will not occur because organisms will not waste time or energy in a pointless fight. (Unlike humans, who compete all the time for various things that do nothing to increase reproduction or survival.) The fierceness of a particular competitive interaction is usually directly related to how much two species’ niches overlap. This should make sense, given what you just learned about what comprises a niche. If the niches for two different species contain the same food item or the same living space, then members of those species will be in conflict with one another for those parts of their niches.
Keep in mind that competition for limited resources can occur between individuals of different species, and it can occur between individuals of the same species. The first kind of competition is called interspecific competition, or between-species competition, and the second kind is called intraspecific competition, or within-species competition.
While competitive interactions can sometimes involve physical contact between organisms, like a bull elk fighting for a mate, often, the individuals involved do not even know they are competing with each other; they are just moseying along, trying to grow, survive and reproduce. Because of this, it is sometimes difficult for an ecologist to identify competitive interactions, let alone measure their effects! Poor ecologists. Our hearts go out to them.
Still, however keen a competitive interaction might become, it never lasts forever. Few things do. Life lesson. You're welcome.
Competitive interactions can end in one of two ways:
The first result, or when one species wins, is called competitive exclusion. The second, or when both species adapt and "learn" to get along, is called resource partitioning. We discuss the evolutionary consequences of both competitive exclusion and resource partitioning in a Theme on Evolution.
Even sperm compete! Sperm competition is when a female mates with more than one male, and the sperm compete to fertilize one egg. This occurrence is thought to produce the most viable offspring and contribute to diversity in the population.