togetherness function

Calculates the number of identical co-presences and co-absences for species-on-islands

Togetherness, or T-score, describes the level of similarity in the distributional pattern of two species. Originally proposed by Stone & Roberts (1992) for biogeographical situations can it also be applied e.g. to pollinators on different host plants.

togetherness(web, normalise=TRUE, FUN = mean, ...)

Arguments

• web: A matrix with binary or counted interactions/links, where the higher trophic level is represented by columns.
• normalise: Logical; shall index be normalised to a range of 0-1?
• FUN: The function to summarise species-pair T-scores with; defaults to mean.
• ...: Arguments passed on to FUN, especially na.rm=T or colours for hist.

Returns

Returns the average (default) togetherness of all species combinations.

References

Stone, L. and Roberts, A. (1992) Competitive exclusion, or species aggregation? An aid in deciding. Oecologia 91 , 419--424

Author(s)

Carsten F. Dormann

See Also

C.score for another of Stone & Roberts' indices.

Examples

(m <- matrix(c(0,1,0,0,1,1,0,1,1,0), ncol=2, byrow=TRUE))
togetherness(m)
# or, with two togethernesses:
(n <- matrix(c(0,1,1,0,1,1,0,0,1,1,0,1,0,1), ncol=2, byrow=TRUE))
togetherness(n, normalise=FALSE)

data(Safariland)
togetherness(m)