Just add a third column with link strength to the association matrix plotCophylo2 <- function (x, y, assoc = assoc, use.edge.length = use.edge.length, space = space, length.line = length.line, gap = gap, type = type, return = return, col = col, show.tip.label = show.tip.label, font = font) { if(ncol(assoc)==2) { assoc <- cbind(assoc,rep(1,nrow(assoc))) } res 











Zero Inflated Models and Generalized Linear Mixed Models with R.
Zuur, Saveliev, Ieno (2012).