Transcript Ecological Niche Factor Analysis-ENFA

Ecological Niche Factor AnalysisENFA
Gonzalo Rivas
Spring 2010
Introduction to ENFA
• Species are expected to
be non-randomly
distributed due to
ecological and
geographical variables.
Copyright: Basille et al. 2008
Variables
& Spatial location
Location of individuals
Soil type
Canopy structure
Streams
Topography
Monroe County, New York. Copyright © 2010
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
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”).
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”
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.
• 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.