CADDIS Volume 4: Data Analysis

## Predicting Environmental Conditions from Biological Observations (PECBO) Appendix

- Introduction

- Using Existing Taxon-Environment

Relationships - Estimating Taxon-Environment

Relationships - Computing Inferences

- R Scripts

##### Topics in Estimating Taxon-Environment Relationships

## Environmental Limits

Taxon-environment relationships expressed in terms of *environmental limits* attempt to capture the maximum or the minimum level of an environmental variable under which a taxon can persist. Environmental limits can be estimated by computing cumulative percentiles (CPs) from field data. An empirical CP is estimated for a given value of the environmental variable, *x _{0}*, as follows:

where *I* = 1 if *x _{i}* <

*x*and

_{0}*I*= 0 if

*x*>

_{i}*x*, and other variables are as defined in Equation 1. For presence/absence data, the numerator is the number of occurrences of taxon

_{0}*j*at sites in which the value of the environmental variable is less than the cutoff value, and the denominator is the total number of occurrences of taxon

*j*. Plots of CP as a function of

*x*are shown in Figure 4 for two genera. An environmental limit would be estimated by fixing CP at a prescribed value and then computing the

_{0}*x*that corresponds to that value of CP for each taxon. Then,

_{0}*x*quantifies the limiting conditions for that taxon. To estimate the maximum level of an environmental variable under which a taxon could persist, CP would be fixed at a relatively high value (e.g., 0.75).

_{0}Statistical scripts for calculating cumulative percentiles are available under the R Scripts tab of this section.

#### Biological inference

Once environmental limits are computed for each taxon, one can use them to infer conditions at a new site based only on biological observations by computing a weighted average inference.

**Estimating Taxon-Environment Relationships:** Overview Previous Next