a binary presence-absence matrix in which rows are species and columns
are sites.
Value
Returns the number of unique species combinations represented by
the different columns (= sites) in the matrix.
Details
In Diamond's (1975) assembly rules model, species interactions lead to
certain "forbidden combinations" of species. A set of communities structured
this way should contain fewer species combinations than expected by chance.
References
Diamond, J.M. 1975. Assembly of species communities. p. 342-444 in:
Ecology and Evolutoin of Communities. M.L. Cody and J.M. Diamond (eds.).
Harvard University Press, Cambridge.
Pielou, D.P. and E.C. Pielou. 1968. Association among species of infrequent
occurrence: the insect and spider fauna of Polyporus betulinus (Bulliard) Fries.
Journal of Theoretical Biology 21: 202-216.