latitudinal gradients

15
Latitudinal gradients Species – latitude relationship of birds across the New World show the typical pattern of increased species diversity towards the equator. 0 300 600 900 1200 1500 -80 -40 0 40 80 Latitude Number of species

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1500. 1200. 900. Number of species. 600. 300. 0. -80. -40. 0. 40. 80. Latitude. Latitudinal gradients. Species – latitude relationship of birds across the New World show the typical pattern of increased species diversity towards the equator. Coral reef fish. Labridae. - PowerPoint PPT Presentation

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Page 1: Latitudinal gradients

Latitudinal gradients

Species – latitude relationship of birds across the New World show the typical pattern of increased species diversity towards the equator.

0

300

600

900

1200

1500

-80 -40 0 40 80

Latitude

Num

ber o

f spe

cies

Page 2: Latitudinal gradients

020406080

100120140

0 100 200Distance from center of

diversity

Spe

cies

0102030405060

0 100 200Distance from center of

diversity

Day

s of

pel

agic

la

rval

dur

atio

n

0102030405060

0 100 200Distance from center of

diversity

Spe

cies

05

101520253035

0 100 200Distance from center of

diversity

Day

s of

pel

agic

la

rval

dur

atio

n

Coral reef fish

Labridae

Pomacentridae

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.

Mora et al. 2003

Page 3: Latitudinal gradients

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-80 -60 -40 -20 0 20 40 60 80

Latitude

Spe

cies

Latitudinal gradient in species diversity of mollusks on North and South American Pacific shelves (Valdovino et al. 2003)

• 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

Page 4: Latitudinal gradients

The general patterns

Hillebrand (2004) conducted a meta-analysis about 581 published latitudinal gradients

Variable Local samples Regional samplesBody size 0.0001 0.001Thermoregulation 0.74 0.88Dispersal type 0.11 0.03Trophic level 0.03 0.0001Longitude 0.08 0.0001Hemisphere 0.32 0.08Realm 0.01 0.0001Habitat 0.0002 0.0001Grain 0.14 0.69Range 0.82 0.99Global richness 0.24 0.37

Data obtained from

Latitude

Spe

cies

rich

ness

z

Scale

Regional

Local

Latitude

Spe

cies

rich

ness

z

Global richness

High

Low

Latitude

Spe

cies

rich

ness

z

Body size

High

Low

Latitude

Spe

cies

rich

ness

z

Trophic level

High

Low

Latitude

Spe

cies

rich

ness

z

Longitude

Atl, NW

Pac, In, EuA, AuA

Latitude

Spe

cies

rich

ness

z

Realm

Terrstrial, Marine

Freshwater

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

Page 5: Latitudinal gradients

Counterexamples

These taxa are most species rich in the northern Hemisphere

Soybean aphid, Photo by David VoegtlinThe sawfly Arge coccinea, Photo by Tom Murray

The ichneumonid Arotes sp., Photo by Tom Murray

The aquatic macrophyte Hydrilla verticilliata, Photo by FAO

Page 6: Latitudinal gradients

Some theories that try to explain observed latitudinal gradients in species diversity.

Older theories:Environmental stabilityor predictability (Klopfer 1959)Productivity(Slobodkin and Sanders 1969)Heterogeneity (Pianka 1966)Latitudinal decrease in angle of sun ( Terborgh 1985)Aridity (Begon et al.. 1986)Seasonality (Begon et al.. 1986)Number of habitats (Pianka 1966)Latitudinal ranges (Rapoport 1982)Area (Connor and McCoy 1979)

Circular explanations:Competition ( Dobshansky 1950)Predation Paine 1966)Niche width (Ben Eliharu and Safriel 1982)Host diversity(Rhode 1989)Epiphyte load (Strong 1977)Population size (Boucot 1975)

Time related explanations:Temperature dependence of chemical reactions (Alekseev 1982)Temperature dependent mutation rates

Evolutionary time (Pianka 1966)Ice age refuges (Pianka 1988)

Energy related explanations:Energy supply (Rhode 1992)

Range size related explanation:Random range sizes (Colwell and Hurtt 1994) (Gillooly et al. 2005)

Page 7: Latitudinal gradients

0

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-80 -60 -40 -20 0 20 40 60 80Latitude

SRed data points: Multihabitat gradient

in ant species diversity

Blue data points: Gradient for one habitat type

North American grasshoppers

Latitudinal gradients can also be found within single habitat types

Habitat heterogeneity

Energy or area per se

Ant species richness is significantly correlated to mean annual temperature and mean primary production, but not to area

Page 8: Latitudinal gradients

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.

Page 9: Latitudinal gradients

-80-60-40-20

020406080

-80 -60 -40 -20 0 20 40 60 80

Latitude

T

Max T

Min T

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-80 -60 -40 -20 0 20 40 60 80

Latitude

D T

Temperature difference

Species diversity and temperature

Page 10: Latitudinal gradients

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0 10 20 30

Mean temperature

Spe

cies

rich

ness

z

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0 10 20 30

Mean temperature

Spe

cies

rich

ness

z

Western Atlantic gastropods Eastern Pacific gastropods

Biodiversity and temperature

Species diversity of marine gastropods is significantly correlated with mean surface water temperature

Page 11: Latitudinal gradients

Metabolic theory and species latitudinal gradients in species richness

3/ 4 E / kT E / kT3/ 4 3/ 4

M M 1M W e e ln E / k CW W T

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.

Biological times should scale to body weight to the quarter power

Examples: Generation time, lifespan, age of maturation,

average lifetime of a species

E1/ 4 ktt w e

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

E1/ 4 kt1r w e

t

Page 12: Latitudinal gradients

The rate of DNA evolution predicted from metabolic theory

3/ 4 E / kT 1/ 4 E / kTMM W e W eW

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/W1/ 4 E / kTM / W W ea a

1/ 4 E 1ln( W ) Ck T

a

• 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)

kT 1ln( e ) ln(W) C4

a

Page 13: Latitudinal gradients

3/ 4 E / kT 3/ 4 E / kTM W e ; N W e NM C

Diversity and temperature

The energy equivalence rule

3/ 4 E / kT 3/ 4 E 1NM NW e C ln(NW ) ck T

The average abundance N of an assemblage of S species and J individuyals in areal A is N=J/SA

3/ 4 E / kT

3/ 4 E / kT

JB NM W e CSA

J W eSCA B

J E 1ln(S) ln( )k TCAB

For standard areals and species of similar body size holds therefore

E 1ln(S) Ck T

• Species richness should increase with environmental temperature

• Species richness should increase with energy

• The slope of this relationship should be -E/k = -7541K

Caveats:• Mean abundance per unit area is

independent of temperature. • The energy equivalence rule holds at least

approximately and its slope is independent of temperature.

Page 14: Latitudinal gradients

0

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0.0032 0.0034 0.0036 0.0038 0.004

1/T

S

S=e

z=-10005

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0.003 0.003 0.003 0.004 0.004 0.004

1/T

S

z=-8540

0

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0.0032 0.0034 0.0036 0.0038 0.004

1/T

S

z=-10250

0

20

40

60

80

100

0.0033 0.0034 0.0035 0.0036 0.0037

1/T

S

z=-10810

North American

trees

Costa Rican trees along an elevational gradient

North American

amphibians

Ecuadorian amphibians

Fish species richness Prosobranchia species richness Ectoparasites of marine teleosts

0

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600

800

0.0032 0.0034 0.0036 0.0038 0.004

1/T

S

z=-9160

0200

400600800

1000

1200

0.0032 0.0033 0.0034 0.0035 0.0036 0.0037

1/T

S

z=-7170

0

5

10

15

20

25

0.0033 0.0034 0.0035 0.0036 0.0037

1/T

S

z=-8510

Page 15: Latitudinal gradients

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.

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