measuring functional diversity from multiple...
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Measuring functional diversity from multiple traits
Etienne Laliberté, PhD candidateRural Ecology Research Group (RERG)School of Forestry, University of Canterbury, Christchurch, New Zealand
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Functional diversity (FD)
• Functional composition: the value of species traits
• Functional dispersion: the spread, or variability, of species traits
• How to measure FD from multiple traits?
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Sébastien Villéger et al 2008 EcologyAugust issue
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Figure taken from Villéger et al 2008 Ecology
Species 1
Species 2
etc…
9 species in functional trait space (2 traits)
Size of black circle = relative abundance
Functional trait space
Trait 1
Trai
t 2
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Figure taken from Villéger et al 2008 Ecology
Functional richnessFRic
Functional richness (FRic):
Volume of the minimum convex hull that includes all species
Amount of functional space filled by a community
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Figure taken from Villéger et al 2008 Ecology
Functional divergenceFDiv Functional divergence (FDiv):
The divergence of species from the center of gravity of the convex hull
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Functional dispersion:
… the spread, or variability, in the locations of the S species in the T-dimensional space
This concept is termed dispersion in statistics (e.g. SS, variance, SD, range, etc)
Back to the basics
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Figures taken from Villéger et al 2008 Ecology
FRic FDiv
• Sensitive to outliers• Strongly positively correlatedwith species richness
• Does not consider abundances• Need at least 3 species• Need more species than traits
Problems with FRic and FDiv
• Sensitive to outliers• Not sensitive to the sizeof the convex hull
• Need more species than traits• Need at least 3 species
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0 1 2 3 40
1
2
3
4
Trait 1
Trai
t 2FDiv = 0.808
FDiv = 0.808
FDiv does not measure relative differencesin functional dispersion
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Laliberté and Legendre submitted
0 1 2 3 40
1
2
3
4
Trait 1
Trai
t 2
Centroid
Distance of species A to group centroid
A
FDis = average distance to centroid
Functional dispersion (FDis)
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0 1 2 3 40
1
2
3
4
Trait 1
Trai
t 2
Centroid
FDis and relative abundances
Centroid shifts towards the more abundant species
Laliberté and Legendre submitted
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0 1 2 3 40
1
2
3
4
Trait 1
Trai
t 2FDis = 1.395FDiv = 0.808
FDis = 0.697FDiv = 0.808
FDis measures relative differences infunctional dispersion
Laliberté and Legendre submitted
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Figure taken from Villéger et al 2008 Ecology
Simulations of Villéger et al
FRic is positively relatedto species richness
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FDis is not influenced by
species richness
5 15 25 35 45
0.5
1.0
1.5
2.0
2.5
3.0
3.5
a
Species richnessFD
is
r = 0.061
0.0 0.2 0.4 0.6
0.5
1.0
1.5
2.0
2.5
3.0
3.5
FRic
FDis
b r = 0.313
0.2 0.4 0.6 0.80.5
1.0
1.5
2.0
2.5
3.0
3.5
c
FEve
FDis
r = -0.007
0.4 0.6 0.8 1.00.5
1.0
1.5
2.0
2.5
3.0
3.5
FDivFD
is
d r = 0.166Positively
related to FRic and to a lesser
degree FDiv
Laliberté and Legendre submitted
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Desirable properties of FDis
1) Intuitive2) Can use multiple traits (any number or type)3) Less sensitive to outliers4) Direct comparison of functional dispersion5) Min. 2 species (3 for FRic and FDiv)6) Independent of species richness7) Can integrate relative abundances
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dbFD: R function to measure FD
• www.elaliberte.info• Any type of traits (continuous, categorical, ordinal)• Tolerates missing trait values• 3 indices of Villéger et al, plus FDis• Community-weighted trait means (CWM):
functional composition• Functional group richness (FGri)
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Acknowledgements
for fundingto come here
for generousscholarships
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Talk at ESA
Global patterns of plant response diversity with land use intensification
Thursday, after morning tea