Taxon-environment relationships based on absolute or relative abundance data also can be modeled, but the regression models for doing this become more complex. The use of presence/absence data, rather than abundance data, is recommended in most cases.
The abundance of a given taxon can be difficult to model statistically because the abundance values vary strongly from no individuals to hundreds, or thousands of individuals. Because of this variance, and because abundance values are strictly positive, the distribution of the sampling error for abundance observations are often assumed negative binomial (White and Bennets 1996).
Relationship between relative abundance and temperature for Heterlimnius and Malenka. Solid line is mean relationship determined between abundance and temperature determined by a negative binomial regression. Dotted lines are estimated 90% confidence limits about the location of the mean relationship. Open circles represent average relative abundance in approximately 10 samples surrounding the indicated temperature.