Interspecific competition is competition between individuals of different species for the same resources, such as food, light, water, nesting sites or space. It happens where the niches of two species overlap.When two species compete, each has less of the shared resource than it would have alone. This reduces the population size of both species, because less food, space or light means lower survival and fewer offspring.If one species is better adapted to the conditions, it obtains more of the resource. Its population grows while the other's declines. If the conditions stay the same, the less well adapted species may be removed from the habitat completely. This is competitive exclusion: two species cannot share exactly the same niche.Example: red and grey squirrels
Grey squirrels were introduced to Britain from North America in the 19th century. They eat many of the same foods as the native red squirrel, but they can digest acorns more efficiently and are larger. Where the two species compete in broadleaf woodland, red squirrel numbers have fallen and they have disappeared from most of England and Wales.Interspecific competition is not always so extreme. Often two species share a resource but each keeps a slightly different niche, for example by feeding at a different time or in a different place, and both populations persist at lower numbers.When interpreting data, remember that a correlation between one species increasing and another decreasing does not prove competition: other factors, such as disease, may also be involved.
Grey squirrels were introduced to Britain from North America in the 19th century. They eat many of the same foods as the native red squirrel, but they can digest acorns more efficiently and are larger. Where the two species compete in broadleaf woodland, red squirrel numbers have fallen and they have disappeared from most of England and Wales.Interspecific competition is not always so extreme. Often two species share a resource but each keeps a slightly different niche, for example by feeding at a different time or in a different place, and both populations persist at lower numbers.When interpreting data, remember that a correlation between one species increasing and another decreasing does not prove competition: other factors, such as disease, may also be involved.