bipartite (version 2.05)

PDI: Paired Differences Index

Description

Computes the Paired Differences Index

Usage

PDI(web, normalise=TRUE, log=FALSE)

Arguments

web

A bipartite interaction web, i.e.~a matrix with higher (cols) and lower (rows) trophic levels.

normalise

Logical; divides for each species by the maximum of interactions. Thereby species can be compared among each other and values range between 0 and 1. Defaults to TRUE, which differs from Poisot et al. (2011a). Note that Tim Poisot also recommends the norma

log

logical; since number of interactions is often highly skewed, the log yields a more even spread of PDI-values across species. Defaults to FALSE.

Value

• Returns a vector with PDI values between 0 (perfect generalist) and 1 (perfect specialist).

encoding

UTF-8

Details

There are many ways to skin a cat. This is a more recent addition proposed by Poisot et al. (2011a) and used for mutualistic network analysis by Poisot et al. (2011b). This function can be used alone or through specieslevel.If P is interaction strength (typically interaction frequency or proportion depending on argument normalized), then PDI for this species is computed as: sum(P1 - Pi) /(H-1), where P1 is the highest number of interactions in a link, while Pi are the remaining values. H is the number of potential interactors (e.g. plant species if the target species is a pollinator).

References

Dormann, C.F. (2011) How to be a specialist? Quantifying specialisation in pollination networks. Network Biology 1, 1--20 Poisot, T., Lepennetier, G., Martinez, E., Ramsayer, J., and Hochberg, M.E. (2011a) Resource availability affects the structure of a natural bacteria-bacteriophage community. Biology Letters 7, 201--204 Poisot, T., Bever, J.D., Nemri, A., Thrall, P.H., and Hochberg, M.E. (2011b) A conceptual framework for the evolution of ecological specialisation. Ecology Letters 14, 841--851 Poisot, T., E. Canard, N. Mouquet, and M. E. Hochberg. 2012. A comparative study of ecological specialization estimators. Methods in Ecology and Evolution 3, 537--544. doi: 10.1111/j.2041-210X.2011.00174.x.

See Also

See also specieslevel.

Examples

data(Safariland)
PDI(Safariland) # for pollinators
PDI(t(Safariland), log=TRUE) # for plants