Interspecific competition is competition between individuals of different species for the same limited resources, such as food, water, light, space, minerals or nesting sites.When two species compete, the resources available to each are reduced. Each population therefore has less energy for growth and reproduction, so both populations are usually smaller than they would be if the other species were absent.If one species is better adapted to obtaining the shared resource, it will outcompete the other. This is summarised by the competitive exclusion principle: two species cannot occupy exactly the same niche in the same habitat indefinitely; one will eventually be eliminated from that area. Where two species do coexist, their niches usually differ slightly (for example they feed at different times or on different parts of a plant).Example 1: red and grey squirrels. Grey squirrels were introduced into the UK from North America in the 19th century. They compete with native red squirrels for food and habitat; grey squirrels are larger, can digest acorns more efficiently, and carry squirrelpox virus, which kills red squirrels. Red squirrels have been replaced across most of England and survive mainly in Scotland, parts of northern England and a few isolated areas.Example 2: Paramecium. When Paramecium aurelia and Paramecium caudatum are grown separately, both populations grow well. When grown together in the same culture, P. aurelia outcompetes P. caudatum for food and P. caudatum dies out.