Whether you look at plants, wild animals or humans, you will find that the world’s resources are limited. This leads to a natural phenomenon: competition. Though much of the competition biology teachers discuss is interspecific competition -- competition between different species -- competition within species, called intraspecific competition, is also an important driver of organisms' behavior. Many different types of competition between members of the same species exist. Their differences often slight, these types of competition explain themselves better through example.
Intra Versus Inter
The prefix “intra” means “within.” Scientists label competition between organisms of the same species as “intraspecific” competition. Such competition is almost always present in a species, but is more prevalent and obvious under certain situations. According to Richard Lockshin, a cellular biologist at St. John’s University and author of the book, “The Joy of Science: An Examination of How Scientists Ask and Answer Questions Using the Story of Evolution as a Paradigm,” when a species’ population grows significantly larger, when resources decline or when a group of organisms begins to pack together closely in a tight space, intraspecific competition intensifies. The overall principle driving intraspecific competition is the struggle to obtain the limited resources in an environment.
Interference: Not Just in Football
Perhaps the easiest type of intraspecific competition to understand is inference competition. In this form of competition, members of the same species “interfere” with one another when acquiring resources. In some cases, organisms literally fight for resources, which you might see if you own a small tank with many shrimp. In other cases, organisms “outgrow” one another so as to acquire more resources. For example, some trees grow taller than others to obtain more sunlight.
Exploitation: Not Just for Politicians
While interference competition is usually obvious in that you can see organisms fighting or organisms of clearly different sizes, exploitation competition is virtually invisible. Exploitation competition is a form of competition in which resources are “held” instead of competed for. In this type of competition, members of the same species might never even make contact with their competitors. For example, in the bird community, unwritten codes not to encroach on others’ territories allow for few fights and direct conflicts. Birds hold an area of resource-rich land in their environment, marking their territory with self-designed rock patterns or nests and singing songs to let others know, “this is my turf.”
Sexual Competition: Charming Females by Any Means Necessary
Not all competition is for natural resources. Organisms must also compete within their species to mate and spread their genes. In the natural world, males compete among one another for females, which are a limiting resource; a male that does not mate loses the chance to pass on his genes. Because females have the power to choose the males with which they mate, males compete, sometimes with showy displays and sometimes with aggressive battles, to attract females. This competition might be direct behavior between two or more males, as in male gorillas fighting for a harem of females. It can also be indirect displays of genetic quality, as in peacocks showing off their long, colorful feathers, which peahens prefer to shorter, duller feathers.
- The Joy of Science: An Examination of How Scientists Ask and Answer Questions Using the Story of Evolution as a Paradigm; Richard Lockshin
- Western Michigan University: Intraspecific Competition (PDF)
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