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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.

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Latitudinal gradients

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Latitudinal gradients

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.


Latitudinal gradients

Coral reef fish

Labridae

Pomacentridae

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 gradients

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


Latitudinal gradients

The general patterns

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

  • 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


Counterexamples

Counterexamples

The sawfly Arge coccinea, Photo by Tom Murray

Soybean aphid, Photo by David Voegtlin

The ichneumonid Arotes sp., Photo by Tom Murray

The aquatic macrophyte Hydrilla verticilliata, Photo by FAO

These taxa are most species rich in the northern Hemisphere


Latitudinal gradients

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

Older theories:

Circular explanations:

Environmental stability

Competition

(

Dobshansky

1950)

or predictability

Predation

(

Klopfer

1959)

Paine 1966)

Productivity

Niche width

(

Slobodkin

and Sanders 1969)

(Ben

Eliharu

and

Safriel

1982)

Heterogeneity

Host diversity

(

Pianka

1966)

Latitudinal decrease in

(Rhode 1989)

angle of sun

Epiphyte load

(

Terborgh

1985)

(Strong 1977)

Aridity

Population size

(

Begon

et al.. 1986)

(

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:

(Alekseev 1982)

chemical reactions

Random range sizes

Temperaturedependent mutationrates

(Colwell and

Hurtt

1994)

(Gillooly et al. 2005)

Evolutionary time

Energy related explanations:

(

Pianka

1966)

Energy supply

Ice age refuges

(Rhode 1992)

(

Pianka

1988)


Latitudinal gradients

Habitat heterogeneity

North American grasshoppers

Red data points: Multihabitat gradient in ant species diversity

Blue data points: Gradient for one habitat type

Latitudinal gradients can also be found within single habitat types

Energy or area per se

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


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.


Latitudinal gradients

Species diversity and temperature


Latitudinal gradients

Biodiversity and temperature

Western Atlantic gastropods

Eastern Pacific gastropods

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


Latitudinal gradients

Metabolic theory and species latitudinal gradients in species richness

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

Biological times should scale to body weight to the quarter power

Examples: Generation time, lifespan, age of maturation, average lifetime of a species

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.


Latitudinal gradients

The rate of DNA evolution predicted from metabolic theory

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

  • 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)


Latitudinal gradients

Diversity and temperature

The energy equivalence rule

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

  • 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.

For standard areals and species of similar body size holds therefore


Latitudinal gradients

Costa Rican trees along an elevational gradient

North American trees

North American amphibians

Ecuadorian amphibians

Prosobranchia species richness

Ectoparasites of marine teleosts

Fish species richness


Latitudinal gradients

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.


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