The diversity of species is a primary measure of the ecological health of a place. In 1609 Mannahatta was remarkable for its species diversity. The past 400 years have changed that species diversity dramatically, both through loss of some native species and by introduction of species from other parts of the world. Human beings interact with these species in urban environments through direct control measures and indirectly by providing regular food supplies. There is also some evidence of relaxed predation pressure in cities. These factors tend to favor strong competitors whose abundance may lead to competitive exclusion of other species (Faeth et al. 2005; Marzluff 2008; Melles et al. 2003; Chance & Walsh 2006). Finally the built environment substitutes habitats like buildings and pavement for ecosystems like forests and wetlands. There is some evidence that the built environment has species associations most closely related to cliff habitats and secondarily grasslands (c.f. Lundhom & Richardson 2010). Through the method below, we try to include all of these factors to make some predictions about spontaneously occurring species (i.e. not agriculture or garden species).
First we estimate the potential species richness based on area-climate proxy relationships, then suggest a species composition that fills that diversity based on the habitat qualities of the area of interest. Species are assigned by probability of occurance, with higher probabilities associated with strongly competitive species in each taxa.