Download Species Diversity

Species Diversity
Biogeography
November 7-14, 2007
Geographical Ecology

Ecological Patterns




Species diversity
Species distributions
Island patterns
Community
distributions

Ecological Processes




Competition
Coexistence
Succession
disturbance
Species Diversity

Measuring Diversity





Scales
Richness
Diversity
Eveness

Processes Explaining
Diversity Gradients


•
•
•
•
•
Patterns of Diversity





Latitudinal gradients
Elevational gradients
Precipitation gradients
Peninsulas
Aquatic environments
Historical Disturbance
Hypothesis
Equilibrium Theories

Productivity
Climate stability
Heterogeneity
Biotic interaction
Area/distance
Diversity in TRF
• Equilibrium theory
• Janzen’s hypothesis
• Non-Equilibrium theory
Species Diversity: A NonConcept?
 What
determines the number and kinds of
species that occur in a particular place?
 Why
do number and kinds of species vary
from place to place?
How many species are there?
How many species are there?
Scales of Diversity
 Alpha

w/in habitat
 Beta

Diversity
Diversity
b/w habitat
 Gamma

Diversity
Total diversity
Species
Woodland habitat
Hedgerow Habitat
A
x
B
x
C
x
D
x
E
x
F
x
x
G
x
x
H
x
x
I
x
x
J
x
x
K
x
L
x
Open field habitat
x
M
x
N
x
Alpha Diversity
Beta Diversity
Gamma Diversity
Species
Woodland habitat
Hedgerow Habitat
A
x
B
x
C
x
D
x
E
x
F
x
x
G
x
x
H
x
x
I
x
x
J
x
x
K
x
L
x
Open field habitat
x
M
x
N
x
Alpha Diversity
Beta Diversity
Gamma Diversity
10
7
3
Species
Woodland habitat
Hedgerow Habitat
A
x
B
x
C
x
D
x
E
x
F
x
x
G
x
x
H
x
x
I
x
x
J
x
x
K
x
L
x
Open field habitat
x
M
x
N
x
Alpha Diversity
Beta Diversity
Gamma Diversity
10
(W vs. H) = 7
7
3
Species
Woodland habitat
Hedgerow Habitat
A
x
B
x
C
x
D
x
E
x
F
x
x
G
x
x
H
x
x
I
x
x
J
x
x
K
x
L
x
Open field habitat
x
M
x
N
x
Alpha Diversity
Beta Diversity
Gamma Diversity
10
7
(W vs. H) = 7
(H vs. F) = 8
3
Species
Woodland habitat
Hedgerow Habitat
A
x
B
x
C
x
D
x
E
x
F
x
x
G
x
x
H
x
x
I
x
x
J
x
x
K
x
L
x
Open field habitat
x
M
x
N
x
Alpha Diversity
Beta Diversity
Gamma Diversity
10
7
3
(W vs. H) = 7
(H vs. F) = 8
(F vs. W) = 13
Species
Woodland habitat
Hedgerow Habitat
A
x
B
x
C
x
D
x
E
x
F
x
x
G
x
x
H
x
x
I
x
x
J
x
x
K
x
L
x
Open field habitat
x
M
x
N
x
Alpha Diversity
Beta Diversity
Gamma Diversity
10
7
3
(W vs. H) = 7
(H vs. F) = 8
(F vs. W) = 13
14
Sampling area and species richness
Relationship b/w sampling area and bird species richness in North America (Fig. 14.1 MacDonald)
Measuring Diversity

Species Richness



Species Diversity


Total number of species in an area
can also be measured as biomass, basal area, % cover
Considers eveness and richness
Species Eveness

Considers how abundance data are distributed among the
species
96 humans, 1 dodo, 1 thylacine, 1 honeycreeper, 1 chuckwalla
20 peccaries, 20 monkeys, 20 leafcutter ants, 20 wasps, 20 lizards
Measuring Species Diversity

Species Richness



The number of species in a given area (N0)
Sample Size Issue!
Margalef Index
Mehinick Index
R1 = S-1/ln(n)
R2 = S/√n
Where S = total number of species in area sampled
n = total number of individuals observed
Interpretation:
The higher the index the greater the richness
Example: S = 6 and n = 50
S = 6 and n = 20
R1 = 1.28
R1 = 1.66
Measuring Species Diversity
 Diversity
Indices - Simpson’s Index 
 = probability that 2 individuals selected
at random will belong to the same species
= i(ni(ni-1))/N(N-1)
Where:
ni= total number of individuals in each species
N = Total number of individuals in all species
Interpretation:
If probability is high, the diversity of sample is low
Measuring Species Diversity
 Diversity
Indices - Shannon’s Index H’
H’= -i ((ni/N) ln (ni/N))
Where:
ni= total number of individuals in each species
N = Total number of individuals in all species
Interpretation:
1.5 (low richness/eveness) to 3.5 (high richness and eveness)
Hill’s Family of Diversity
Numbers
 Units
are given in numbers of species
NO = total number of species in the sample
N1 = the number of abundant species
N2 = the number of very abundant species
N1 = eH’ (H’=Shannon’s index)
N2 = 1/ (=Simpson’s index)
Measuring Species Diversity

Species Eveness
How abundance data are distributed among species
96 humans, 1 dodo, 1 thylacine, 1 honeycreeper, 1 chuckwalla
20 peccaries, 20 monkeys, 20 leafcutter ants, 20 wasps, 20 lizards
Modified Hill’s Ratio E5 = N2-1/N1-1
Where: N1 = eH’
N2 = 1/
Interpretation:
0 = less even, 1 = more even
Desert Lizard Diversity
Number of individuals for each of 6 species
of lizards counted in a 1 hectare plot
Lizard Species
Cnemidophorus tesselatus
Number of
Individuals
3
Cnemidophorus tigris
15
Crotophytus wislizenii
1
Holbrookia maculata
1
Phrynosoma cornutum
10
Scleoporus magister
2
TOTAL Individuals
32
Desert Lizard Diversity
Richness
Diversity
NO =
 =
R1 =
H’ =
R2 =
N1 =
N2 =
Eveness
E5 =
Desert Lizard Diversity
Richness
Diversity
NO = 6
 = 0.31
R1 = 1.44
H’ = 1.33
R2 = 1.06
N1 = 4
N2 = 3
Eveness
E5 = 0.80
Patterns of Diversity
 Latitudinal
Gradients
 Elevation Gradients
 Precipitation Gradients
 Peninsulas
 Aquatic Environments
Mammals
Birds
Processes Explaining Diversity
Gradients
• Historical Disturbance Hypothesis
- landscape
reflects historical events, not current
environmental conditions (not in equilibrium)
Habitats catastrophically disturbed are “undersaturated” in terms of species
because there hasn’t been adequate time for adaptation and speciation
Problems: evidence from tropics
Extent of tropics during last glacial maximum
Processes Explaining Diversity
Gradients
 Equilibrium

Theories
Landscape is a reflection of current
environmental conditions (in equilibrium)
•
•
•
•
•
Productivity
Climate stability-Harsh habitat
Habitat heterogeneity
Biotic interactions
Large Area
Processes Explaining Diversity
Gradients
 Productivity

What is the link b/w productivity and
biodiversity?
• Tropics 2200 g/m2/yr
• Temperate 1200 g/m2/yr
• Boreal 800 g/m2/yr

Scale
• Estuaries, marshes are most productive
ecosystems on earth, with lowest diversity
Processes Explaining Diversity
Gradients
 Climate



Stability (Harsh Habitat)
Environments with low stability are harsher
and are less diverse
Why?
Exceptions
• Areas with stable climate but low diversity
Processes Explaining Diversity
Gradients
 Habitat


Diversity (Heterogeneity)
What is the link?
Is it a direct relationship?
Processes Explaining Diversity
Gradients
 Biotic

Interactions
Is speciation driven by competition in low lats
and adaptation to physical stress in high lats?
• Exceptions: trees/plants


What about predation as a mechanism?
Circularity
Processes Explaining Diversity
Gradients
 Large



Land Area
Supports more individs
Supports more species
Tropics? Boreal?
Diversity in TRF and Coral Reefs
 Equilibrium

Viewpoint
Stability is the major characteristic of a
community. Following disturbance, it recovers
and high diversity is maintained by a variety of
mechanisms. Community reflects current
conditions.
 Non-Equilibrium

Viewpoint
Communities rarely reach an equilibrium state
and high diversity results from changing
environmental conditions.
Diversity in TRF
• Janzen’s Hypothesis (1970): Biotic interactions
- host-specific herbivores
- seed predation
- canopy foliovores
• Hubbell’s research (1979, 1980) to support Janzen
• Non-equilbrium explanation (Connell 1978)
- coral reefs
The Non-Equilibrium Hypothesis
(Connell 1978)

Intermediate Disturbance Hypothesis
The Non-Equilibrium Hypothesis
(Connell 1978)
 Connell’s




Conclusions
TRF and Coral Reefs demonstrate Non-Equilibrium
Hypothesis
Equilibrium and Non-Equilibrium are not mutually
exclusive
Bottom line is:
Role of human disturbances
More Intermediate Disturbance
Hypothesis (Denslow 1980)

Intermediate levels of disturbance vary by ecosystem
Ecosyste
m
Prairie
Historic Rate of
Disturbance (years)
2
Chaparral
30
Pine
50
Oak-HW
Spruce-Fir
50-100
1000