Number of species
Latitudinal gradients
1500
1200
900
600
300
0
-80
-40
0
40
80
Latitude
Species – latitude relationship of birds across the New World show the typical
pattern of increased species diversity towards the equator.
Coral reef fish
140
120
100
80
60
40
20
0
Days of pelagic
larval duration
Species
Labridae
0
100
60
50
40
30
20
10
0
200
0
100
200
Distance from center of
diversity
Pomacentridae
60
50
40
30
20
10
0
Days of pelagic
larval duration
Species
Distance from center of
diversity
0
100
200
Distance from center of
diversity
35
30
25
20
15
10
5
0
0
100
200
Distance from center of
diversity
Mora et al. 2003
Diversity of coral reef fish declines from their centres of diversity.
There is also a strong correlation between distance and duration of the pelagic
phase, which is a proxi of dispersal ability.
Latitudinal gradient in species diversity of mollusks on North
and South American Pacific shelves (Valdovino et al. 2003)
Species
1000
800
600
400
200
0
-80 -60 -40 -20
0
20 40 60 80
Latitude
•
Centers of diversity are often shifted north or south
•
Species richness sharply declines towards temperate regions
•
Tropics contain a very large proportion of total species richness
•
Species near the center of species richness are often less dispersive
The general patterns
Latitude
Trophic level
High
Low
Latitude
High
Low
Latitude
Longitude
Atl, NW
Pac, In,
EuA, AuA
Species richness z
Local
Global richness
Species richness z
Regional
Species richness z
Scale
Species richness z
Species richness z
Data obtained from
Variable
Local samples
Regional samples
Body size
0.0001
0.001
Thermoregulation
0.74
0.88
Dispersal type
0.11
0.03
Trophic level
0.03
0.0001
Longitude
0.08
0.0001
Hemisphere
0.32
0.08
Realm
0.01
0.0001
Habitat
0.0002
0.0001
Grain
0.14
0.69
Range
0.82
0.99
Global richness
0.24
0.37
Species richness z
Hillebrand (2004) conducted a meta-analysis about 581 published latitudinal gradients
Body size
High
Low
Latitude
Realm
Terrstrial,
Marine
Freshwater
Latitude
Basic conclusions
•
Nearly all taxa show a latitudinal gradient
•
Body size and realm are major predictors of the strange of the
latitudinal gradient
•
The ubiquity of the pattern makes a simple mechanistic explanation
more probable than taxon or life history type specific
Latitude
Counterexamples
The sawfly Arge coccinea, Photo by Tom Murray
Soybean aphid, Photo by David Voegtlin
The ichneumonid Arotes sp.,
The aquatic macrophyte Hydrilla verticilliata,
Photo by Tom Murray
Photo by FAO
These taxa are most species rich in the northern Hemisphere
Some theories that try to explain observed latitudinal gradients in
species diversity.
Older theories:
Circular explanations:
Environmental stability
Competition (Dobshansky 1950)
or predictability (Klopfer 1959)
Predation Paine 1966)
Productivity
Niche width
(Slobodkin and Sanders 1969)
(Ben Eliharu and Safriel 1982)
Heterogeneity (Pianka 1966)
Host diversity
Latitudinal decrease in
(Rhode 1989)
angle of sun (Terborgh 1985)
Epiphyte load (Strong 1977)
Aridity (Begon et al.. 1986)
Population size (Boucot 1975)
Seasonality (Begon et al.. 1986)
Number of habitats (Pianka 1966)
Latitudinal ranges (Rapoport 1982)
Time related explanations:
Area (Connor and McCoy 1979)
Temperature dependence of
Range size related explanation:
chemical reactions (Alekseev 1982)
Random range sizes
Temperature dependent
(Colwell and Hurtt 1994)
mutation rates (Gillooly et al. 2005)
Evolutionary time (Pianka 1966)
Energy related explanations:
Energy supply (Rhode 1992)
Ice age refuges (Pianka 1988)
Habitat heterogeneity
250
North American
grasshoppers
200
150
Red data points: Multihabitat gradient
in ant species diversity
S
Blue data points: Gradient for one
habitat type
100
50
0
-80 -60 -40 -20
0
20
40
60
80
Latitudinal gradients can also be
found within single habitat types
Latitude
Energy or area per se
Ant species richness is significantly correlated to mean annual temperature and
mean primary production, but not to area
Refuge theory
The refuge theory of Pianka tries to explain the gradient in species diversity from ice age
refuges in which speciation rates were fast. This process is thought to result in a
multiplication of species numbers in the tropics. In the temperate regions without refuges
species number remained more or less constant.
T
Species diversity and temperature
80
60
40
20
0
-20
-40
-60
-80
Max T
Min T
-80 -60 -40 -20
0
20 40 60 80
Latitude
100
DT
80
Temperature
difference
60
40
20
0
-80 -60 -40 -20 0
20 40 60 80
Latitude
Biodiversity and temperature
z
1000
z
1000
800
Species richness
Eastern Pacific gastropods
Species richness
Western Atlantic gastropods
800
600
400
200
0
600
400
200
0
0
10
20
Mean temperature
30
0
10
20
Mean temperature
Species diversity of marine gastropods is significantly correlated with
mean surface water temperature
30
Metabolic theory and species latitudinal gradients in species richness
Biological times should scale to
body weight to the quarter power
Examples: Generation time,
lifespan, age of maturation,
average lifetime of a species
E
1/ 4 kt
tw e
M  W3/ 4e E / kT 
The inverse of time are rates.
Examples: Growth rates, mutation rates,
species turnover rates, migration rates
Hence biological rates should scale to
body weight and temperature by
E

1
r   w 1/ 4e kt
t
M
1
 M 
 E / kT

e

ln


E
/
k
C
 3/ 4 
3/ 4
W
T
W 
Body weight corrected energy use should exponentially scale to the inverse of
temperature.
The slope –E/k should be a universal constant for all species independent of body
size.
The rate of DNA evolution predicted from metabolic theory
3/ 4  E / kT
MW e
M

 W 1/ 4 e E / kT
W
Body size specific metabolic rate M/W should scale to the quarter
power to body weight and exponentially to temperature
Now assume that most mutations are neutral and occur randomly. That is we
assume that the neutral theory of population genetics (Kimura 1983)
DNA substitution rate a should be proportional to M/W
a  M / W  a  W 1/ 4e E / kT
ln(a W1/ 4 )  
E1
C
kT
1
ln(a e kT )   ln(W)  C
4
•
Body weight corrected DNA substitution rates (evolution rates) should be a
linear function of 1/T with slope –E/k = -7541
•
Higher environmental temperatures should lead to higher substitution rates
(faster evolution)
•
Body weight corrected DNA substitution rates (evolution rates) should
decrease with body weight
•
Large bodied species should have lower substitution rates (slower evolution)
Diversity and temperature
The energy equivalence rule
M  W3/ 4eE/ kT ; N  W3/ 4eE/ kT  NM  C
NM  NW 3/ 4e  E / kT  C  ln(NW 3/ 4 ) 
E1
c
kT
The average abundance N of an assemblage of S species and J individuyals
in areal A is N=J/SA
J
• Species richness should increase with
B  NM 
W 3/ 4 e  E / kT  C
environmental temperature
SA
J W 3/ 4 e  E / kT
S
CA
B
J
E1
ln(S)  ln(
)
CAB k T
•
Species richness should increase with
energy
•
The slope of this relationship should be -E/k
= -7541K
Caveats:
For standard areals and species of
similar body size holds therefore
ln(S) 
E 1
C
k T
•
Mean abundance per unit area is
independent of temperature.
•
The energy equivalence rule holds at least
approximately and its slope is
independent of temperature.
200
200
z=-10005
150
S
S
North
American
trees
z=-8540
150
100
50
0
0
0.0032 0.0034 0.0036 0.0038 0.004
0.003 0.003 0.003 0.004 0.004 0.004
1/T
1/T
100
z=-10250
S
S
40
z=-10810
80
60
Ecuadorian
amphibians
60
40
20
20
0
0
0.0032 0.0034 0.0036 0.0038 0.004
0.0033 0.0034 0.0035 0.0036 0.0037
1/T
1/T
Fish species richness
Prosobranchia species richness Ectoparasites of marine teleosts
1200
800
z=-9160
600
25
z=-7170
1000
S
400
600
15
10
400
200
z=-8510
20
800
S
S
100
50
S=e
80
North
American
amphibians
Costa Rican
trees along
an
elevational
gradient
200
5
0
0
0
0.0032 0.0034 0.0036 0.0038 0.004
0.0032 0.0033 0.0034 0.0035 0.0036 0.0037
0.0033 0.0034 0.0035 0.0036 0.0037
1/T
1/T
1/T
Today’s reading
Latitudinal gradients:
http://en.wikipedia.org/wiki/Latitudinal_gradients_in_species_diversity
Gaston K. 2000 - Global patterns in biodiversity - Nature 405: 220-227
Allen A. P., Brown J. H., Gillooly J. F. 2002. Global biodiversity, biochemical
kinetics, and the energy equivalence rule. Science 297: 1545-1548.