The statistical machinery of alien species

Many species of plants are found in regions to which they are alien and their global distribution has been found to exhibit several remarkable patterns,characterised by exponential functions of the kind that could arise through versions of MacArthur's broken stick. We show here that these various patterns are all quantitatively reproduced by a simple algorithm, in terms of a single parameter- a single stick to be broken. This algorithm admits a biological interpretation in terms of niche structures fluctuating with time and productivity; with sites and species highly idiosyncratic. Technically, this is an application of statistical mechanics to ecology quite different from the familiar application to species abundance distributions.