measuring functional diversity from multiple...
TRANSCRIPT
Measuring functional diversity from multiple traits
Etienne Laliberté, PhD candidateRural Ecology Research Group (RERG)School of Forestry, University of Canterbury, Christchurch, New Zealand
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?
Sébastien Villéger et al 2008 EcologyAugust issue
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
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
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
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
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
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
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)
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
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
Figure taken from Villéger et al 2008 Ecology
Simulations of Villéger et al
FRic is positively relatedto species richness
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
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
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)
Acknowledgements
for fundingto come here
for generousscholarships
Talk at ESA
Global patterns of plant response diversity with land use intensification
Thursday, after morning tea