1. Ecological Niche Factor Analysis-ENFA
Gonzalo Rivas
Spring 2010

2. Introduction to ENFA
Species are expected to be non-randomly distributed due to ecological and geographical variables.
Copyright: Basille et al. 2008

3. Variables & Spatial location
Location of individuals
Soil type
Canopy structure
Streams
Topography
Monroe County, New York. Copyright © 2010

4. What is ENFA?
Ecological Niche factor analysis (ENFA) is a multivariate approach to study species distribution based on environmental covariates using presence-only data.
Similar to PCA but is spatially explicit

5. False absence?
ENFA allows us to calculate the optimal range of a species by comparing the distribution of the cells in which the species is occurring with the distribution of the whole set of cells (“background”).

6. By the addition of many variables we can approach this analysis to the concept of ecological niche defined by Hutchinson (1957):
Ecological niche: “the range in the multidimensional space of ecological variables within which a species can maintain a viable population”

7. Advantage of adehabitat-ENFA
It can be used without absence data (such as herbarium and museum collections)
Absence data can be biased: b/c of no detection, historical reasons (false absences) or the habitat is unsuitable (this is what we want to test).
A good tool to construct habitat suitability analysis.
Habitat selection and home range estimation by wildlife.

8. The package adehabitat can be used to import single maps within R and then combine them into multilayer maps.
These maps are grids of pixels on which several variables are measured, allowing multivariate analysis of habitat use by animals/plants.