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Polypore fungi 151 Adhikari, 2000; Authors own unpublished data.

Ectomycorrhizal fungi 225 Adhikari, 2000; Authors own unpublished data.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