Congruence between species richness and human
population density: reconciliation or conflict?
Ole R VETAAS
Unifob – Global, University of Bergen, 5015 Bergen, Norway,
M. CHRISTENSEN
University of Copenhagen, Forest and Landscape, Denmark
Congruence between species richness and human
population density• Human action is often claimed to be the main
cause behind habitat loss and biodiversity reduction.
CONTRADICTION to (?)
• Large parts of the globe have enhanced biodiversity, and at the same time these areas have a high density of people
AREA , ORGANISMS, and RESEARCH QUESTION
• The present study analyses species richness along an elevational gradient
in Nepal Himalayas
• Seven taxonomic groups including: trees, herbaceous plants, ferns, cryptogams,
and fungi• WHAT kind of organism has this
correspondence, and why?
INDIA
TIBET
Cause Effect
?
High Biodiversity High human population
Many Biological options for exploitation
Human settlements
Human settlements
Species rich cultural landscapes
Obscured
Research question 1 Which organism has a correlation between human population density and species richness along the total elevation gradient
organisms with elevation range information
No. of Specieswith info.
Main sources of information
Polypore fungi 151 Adhikari, 2000; Authors own unpublished data.
Ectomycorrhizal fungi 225 Adhikari, 2000; Authors own unpublished data.
Lichens 336 Sharma, 1995; Pandey et al., 2002.
Mosses 464 Kattel & Adhikari, 1992; Bhuju et al., 2007; Grau et al., 2007.
Liverworts 360 Kattel, 2002; Bhuju et al., 2007. Grau et al., 2007.
Ferns 293 Iwatsuki, 1988; Bhattarai et al., 2004; Bhuju et al., 2007.
Trees and herbaceous species 614 / 3300 Hara et al., 1978; Hara & Williams,1979; Hara et al., 1982; Bhattarai & Vetaas, 2006; Vetaas & grytens, 2002Bhuju et al., 2007.
Elevation Gradient
DeciduousDeciduousWarm Warm
temperate-temperate-subtropical subtropical
ForestForest
Ice & rockIce & rockAlpineAlpine
Meadows and heathMeadows and heath
TROPICAL FORESTTROPICAL FOREST
Evergreen OAK-Evergreen OAK-
RHODODENDRON-ForestRHODODENDRON-Forest
MontaneMontaneBETULABETULA
ConiferousConiferousForestForest &…… &……
eleva
spp
no
0 1000 2000 3000 4000 5000 6000
02
00
40
06
00
80
01
00
01
20
0
1000 m a.s.l.
Interpolated species richness
species 100 200 300 400 500 …. 6000
sp1 0 0 1 1 0 0
sp2 1 1 1 1 1 0
sp3 0 0 0 1 1 0
sp n-1 0 0 0 0 1 0
sp n 0 0 0 0 0 0
sum of spp 1 1 2 3 3 0
INTERPOLATION : ASSUMING ALL SPECIES ARE PRESNET IN ALL 100M INTERVALS BETWEEN LOWER AND UPPER ELEVATION LIMIT
This gives total number of species in all different elevation bands from 100 m to 6000 m a.s.l.
Research question 1
Which organism has a correlation between human population density and species richness along the total elevation gradient
Organism Species vs. Human Population
Polypores fungi 0.156 ns
Mycorrhizal fungi
0.541***
Ferns 0.439***
Trees 0.631***
Liverworts -0.187 ns
Mosses -0.024 ns
Lichens -0.038 ns
Herbs 0.10 ns
Scale and patterns
• This large scale pattern may in part be ascribed to the fact that very few people live in very unproductive species-poor areas, such as deserts, sub-arctic-biomes, or high mountains.
• The correspondence between species richness and human density may not be evident at shorter spatial extents such as along an human populated elevation gradient.
Elevation and Human population density: focus 200 - 3100
0,0
50,0
100,0
150,0
200,0
250,0
300,0
350,0
400,0
450,0
Altitude (100 meter bands)
Pe
rso
n p
er
km
2
outlier
Research Question 2: Which organism has correlation between richness and human
population along the populated part of the gradient 200 - 3100 m a.s.l.
organism Species richness cor. Human Population
Trees 0.81
Mycorrhizal fungi 0.25
Herbaceous species -0.55
Liverworts - 0.70
Mosses - 0.58
Lichens - 0.62
Polypores fungi - 0.62
Ferns 0.05 ns
2 3 4 5
50
100
150
200
num
ber
of fe
rns
2 3 4 5
80
120
160
200
num
ber
of tr
ees
2 3 4 5
20
40
60
80
num
ber
of M
ycorr
hiz
a
2 3 4 5
300
500
700
# h
erb
ace
ous
speci
es
2 3 4 5
10
20
30
40
50
60
num
ber
of P
oly
pore
fungi
2 3 4 5
20
40
60
80
100
num
ber
of lic
hens
2 3 4 5
human population density
050
100
150
num
ber
of liv
erw
ort
s
2 3 4 5
human population density
050
100
150
200
num
ber
of m
oss
es
r= 0.81
r= -0.55
r= -0.62
r= -0.58r= -0.70
r= -0.62
r= 0.025
r= ns
Cause effect
High biodiversity High human population
AREA of elevation zones
Species area relationships
Area result
0,0
2000,0
4000,0
6000,0
8000,0
10000,0
12000,0
14000,0
100
300
500
700
900
1100
1300
1500
1700
1900
2100
2300
2500
2700
2900
3100
3300
3500
3700
3900
4100
4300
4500
4700
4900
5100
5300
5500
5700
5900
Altitude (100 meter bands)
Are
a (k
m2)
outliers
Correlations between log (species richness) and log (area) in km 2
for target taxa between 200-3100 m a.s.l.
taxa r
Mycorrhizal fungi
- 0.28
Polypores fungi
- 0.77
Ferns - 0.53
Trees 0.55
Liverworts - 0.80
Mosses - 0.77
Lichens - 0.79
herbs - 0.79
Cause Effect
High human population High biodiversity
Climate Temperature
10 15 20
5010
015
020
0
num
ber
of fe
rns
10 15 20
8012
016
020
0
num
ber
of tr
ees
10 15 20
2040
6080
num
ber
of M
ycor
rhiz
a
10 15 20
300
500
700
# h
erba
ceou
s sp
ecie
s
10 15 20
1020
3040
5060
num
ber
of P
olyp
ore
fung
i
10 15 20
2040
6080
100
num
ber
of li
chen
s
10 15 20
temperature
050
100
150
num
ber
of li
verw
orts
10 15 20
temperature
050
100
150
200
num
ber
of m
osse
s
Forest and people
• Forest cover is influenced by human density
• Forest cover may influence species richness
0%
10%
20%
30%
40%
50%
60%
70%
80%
Altitude (100m bands)
Fo
re
st
co
ve
r (
pe
rc
en
t)
0,0
50,0
100,0
150,0
200,0
250,0
300,0
350,0
400,0
450,0
Altitude (100 meter bands)
Pe
rso
n p
er
km
2
hum
na d
ensu
ty
fo
rest
den
sity
in %
M a.s.l.
log-HUMAN-POPULATION DENSITY and log-FOREST-COVER
2 3 4 5
human population
6.5
7.0
7.5
8.0
fore
st c
over
Cause Effect
High human population High biodiversity
reduced forest cover
Related to Intermediate disturbance hypothesis
More tree richness at low forest cover !
0.2 0.3 0.4 0.5 0.6 0.7
forest area
8010
012
014
016
018
020
0
num
ber
of t
rees
conclusion
• Forest cover predicts tree specie richness• Forest cover is determined by climate at
higher elevation and human density at lower elevation
• Thus people may have a positive impact on tree diversity
• Management implication: a moderate reduction of total forest cover may enhance richness rather than reduce it
Thank you for your attention
Lopped oak forest rich in species
Exploit the dominant species
• This may be done by:
• Selective logging in a forest
• Lopping or pollarding of canopy trees
• Browsing by large mammals
Biodiversity and disturbance
species richnessspecies richness
Increasing disturbance
Theory Intermediate disturbance hypothesis
• Hutchnison (1951), Grime (1973b), and Connell (1978), has suggested that there is higher chance for many species to coexist, when a community or landscape is moderately disturbed.
• This tenet is well accepted, although disturbance is difficult to define and measure
Disturbance definition
• Many different definitions
• Grime: disturbance = reduced or destructed biomass
• Browsing, Grazing, Fire or other biomass outtake are regarded as disturbance
Biodiversity; biomass and disturbance
species richnessspecies richness
increasing biomass increasing disturbance