Nestedness7 is a PC-ORD add-in that calculates nestedness statistics. The basic concept of nestedness is that sample units with few species should tend to have only the most frequent species.  Conversely, rare species are most likely to occur in species-rich sample units, moreso than would be expected by chance (Patterson & Atmar 1986). Theoretical and conservation implications of nestedness have been discussed by Patterson & Atmar (1986), Brualdi & Sanderson (1999), Jonsson (2001) and others.
