Interspecific Competition in Barnacles
Interspecific Competition can be defined as:
a form of competition in which individuals of different species vie for the same resource in an ecosystem (e.g. food or living space). The other form of competition is intraspecific competition, which involves organisms of the same species. (from Wikipedia)
British barnacles are a good organism on which to study both kinds. This section deals with Interspecific competition between lower shore members of the genus Semibalanus and upper shore members of the genus Chthamalus. The first suggestion that competition may exist between species often comes from looking at distribution patterns, usually at a very detailed level. A pattern in a situation where two species occur in the same habitat but generally in different parts of it may indicate the possibility of interspecific competition. So, let us look at the pattern of these two genera on a British rocky shore, click here to go to a transect taken across a rocky wall covered in barnacles. When you have finished that exercise, click Interspecific Competition Page to come back here and carry on.
So, you should have shown yourself that Chthamalus tends to occur higher up the shore that Semibalanus. This is also what connell, and many others had and have found. So, connell asked, why? He talks about his study to answer that question here, it is well worth reading, and quite short. This experiment was important, apart from what it told us about a little studied phenomenon, because it was one of the earlier examples of the experimental approach to ecology, as Connell explains.
The conclusions reached by Connell are now part of the classic case discussed in all the textbooks for interspecific competition and its role in helping to determine where species live.
Other classic studies include those of:
Beaucmap and Ullyot on flatworms
Tansley on Bedstraws
Taniguchi and Nakano on Salmonid fishes
Gause on Paramecium
David Lack on birds species
Broadhead on Book Lice