4 Models of Species Response There are (at least) two models:-Linear - species increase or decrease along the environmental gradientUnimodal - species rise to a peak somewhere along the environmental gradient and then fall again
8 Alpha and Beta Diversity alpha diversity is the diversity of a community (either measured in terms of a diversity index or species richness)beta diversity (also known as ‘species turnover’ or ‘differentiation diversity’) is the rate of change in species composition from one community to another along gradients; gamma diversity is the diversity of a region or a landscape.
11 Inferring Gradients from Species (or Attribute) Data
12 Indirect Gradient Analysis Environmental gradients are inferred from species data aloneThree methods:Principal Component Analysis - linear modelCorrespondence Analysis - unimodal modelDetrended CA - modified unimodal model
35 Making Effective Use of Environmental Variables
36 Direct Gradient Analysis Environmental gradients are constructed from the relationship between species environmental variablesThree methods:Redundancy Analysis - linear modelCanonical (or Constrained) Correspondence Analysis - unimodal modelDetrended CCA - modified unimodal model
40 Partial Analyses Remove the effect of covariates variables that we can measure but which are of no intereste.g. block effects, start values, etc.Carry out the gradient analysis on what is left of the variation after removing the effect of the covariates.