Interspecific competition is competition between individuals of different species for the same limiting resource, for example red and grey squirrels competing for seeds and nuts, or different plants competing for light.Its effects depend on how much the species' needs overlap. Each species has a niche: its role in the ecosystem, including all the conditions and resources it needs. The competitive exclusion principle states that two species cannot occupy exactly the same niche in the same habitat for long. The better competitor will eventually out-compete the other, which dies out locally or moves away.Classic evidence comes from Gause's experiments with two species of Paramecium. Grown separately, P. aurelia and P. caudatum each reached a stable population. Grown together in the same culture with a limited food supply, P. aurelia survived and P. caudatum died out.
In the UK, the introduced grey squirrel has replaced the native red squirrel across most of England. Grey squirrels digest acorns more efficiently, so they get more energy from the same woodland. They also carry squirrelpox, which kills red squirrels.Where niches only partly overlap, both species can coexist, but each has a smaller population than it would have alone. Over time, species may specialise, for example feeding at different heights in a tree, which reduces the overlap. This is called resource partitioning.
In the UK, the introduced grey squirrel has replaced the native red squirrel across most of England. Grey squirrels digest acorns more efficiently, so they get more energy from the same woodland. They also carry squirrelpox, which kills red squirrels.Where niches only partly overlap, both species can coexist, but each has a smaller population than it would have alone. Over time, species may specialise, for example feeding at different heights in a tree, which reduces the overlap. This is called resource partitioning.