CADDIS Volume 4: Data Analysis
Predicting Environmental Conditions from Biological Observations (PECBO) Appendix
- Using Existing Taxon-Environment
- Estimating Taxon-Environment
- Computing Inferences
- R Scripts
Topics in Estimating Taxon-Environment Relationships
Taxon-environment relationships estimated from local data can potentially provide more accurate environmental inferences than the regional-scale relationships provided in the CADDIS database. In this section, different statistical methods for estimating taxon-environment relationships are presented. More extensive details on each of these methods can be found in Yuan (2006).
Before computing taxon-environment relationships, it is important to consider whether you have sufficient data.
The simplest approaches for estimating taxon-environment relationships represent the entire relationship using a single value. This single value can quantify the average conditions that are preferred by a taxon (i.e., the taxon's central tendencies), or it can quantify the limiting environment conditions under which a taxon can persist.
Methods that estimate the entire taxon-environment relationship (rather than a single value) are somewhat more involved, requiring that one solve a regression equation that relates taxon occurrences or abundances to different values of one or more environmental variables. However, once taxon-environment relationships are estimated, one can usually develop more accurate biological inferences.
Two regression approaches are common:
When applying any regression approach, one must consider the following questions:
- How well does the model fit?
- Are there errors in the environmental variables?
- Should survey design weights be incorporated into the regressions?
When entire taxon-environment relationships are available, they can be used to classify taxa into broad categories (e.g., tolerant or intolerant to elevated fine sediments); these classifications can be useful for building biological metrics. Placing taxa into tolerance categories provides guidance on classification of taxa tolerances.
Once taxon-environment relationships have been estimated, different inference methods can be applied to estimate environmental conditions at sites using biological observations.
Estimating Taxon-Environment Relationships: Next