Understanding global biodiversity gradients

Miguel B. AraújoCátedra Rui Nabeiro – Biodiversidade, CIBIO, Universidade de Évora

Museo Nacional de Ciências Naturales, CSIC, Madrid

Gulbenkian, Lisboa, Julho 2009

Causes of global biodiversity gradients

A debate with more than 160 years

Alexander von Humboldt (1769-1859)

Alfred Russel Wallace (1823-1913)

125 Big Questions: What we don’t know?

Contemporary vs. historical hypothesis

“We would challenge anyone who proposes

an historical explanation for the contemporary

patterns of species richness to derive the

predictions of that explanation so that they

may be tested”.

(Kerr & Currie, 1999)

Framing the evolutionary hypothesis

Wiens & Donoghue (2004) TREE

Building of the species pool - Stability

Distribution of the species pool – Niche conservatism

Outline

1.Testing for differential building up of species pool

2.Testing for the effects of niche conservatism

3.Concluding remarks

Araújo et al. 2008 Ecography

Test of historic climate stability hypothesis with European reptiles and amphibians

Temperature PrecipitationHistoric climate stabilityReptiles 0.01 0.01

Amphibians 0.01 0.01

Contemporary climateReptiles 0.01 0.05Amphibians 0.01 ns

Reptile species richness

Amphibian species richness

Simultaneous autoregressive (SAR) models used to assess spatially corrected p values between species richness and contemporary and historical climate

Araújo et al. 2008 Ecography

Total a Total bHistoric climate stabilityReptiles 0.51 0.44Amphibians 0.38 0.26Contemporary climateReptiles 0.43 0.51Amphibians 0.26 0.40

Reptile species richness

Amphibian species richness

Partial regression analysis to separate the unique contribution of the contemporary and historic climate variables

Test of historic climate stability hypothesis with European reptiles and amphibians

Outline

1.Testing for differential building up of species pool

2.Testing for the effects of niche conservatism

3.Concluding remarks

• If diversity gradients are not driven by niche conservatism,

• then we would predict diversity gradients among clades originated in different periods to be similar.

Testing for the effects of niche conservatism – example 1

• If diversity gradients are driven by niche conservatism,

• then we would predict diversity gradients among clades originated in different periods to be different.

• Differences should reflect the ancestral climates shaping species niches.

Testing for the effects of niche conservatism – example 1

Diversity of reptile families – 74% of the World families dated with the fossil record

Families originated in the Cretaceous

Families originated in the Tertiary

Araújo et al. In preparation

Departure from a linear relationship

More families in the Cretaceous

More families in the Tertiary Araújo et al. In preparation

r=0.74

• If diversity patterns are not driven by niche conservatism,

• then the slopes of the diversity gradients should not differ among species originated in different periods.

Testing for the effects of niche conservatism – example 2

• If diversity patterns are driven by niche conservatism,

• then the slopes of the diversity gradients should differ among species originated in different periods:

• Diversity of species originated in warm periods should have steep slopes

Testing for the effects of niche conservatism – example 2

7 132 10 13 3 36 43 14 78 1 15750 650 550 450 350 250 150 50 0my

Variation in slope5 categories

-0,5

0,5

1,5

2,5

Cold climate Warm climate

a)

Romdal, Araújo & Rahbek, In preparation

Slopes from 343 studies assessing

contemporary gradients of diversity for a wide

range of taxa and environments

Testing for the effects of niche conservatism – example 2

Outline

1.Testing for differential building up of species pool

2.Testing for the effects of niche conservatism

3.Concluding remarks

• Climate stability offers a parsimonious explanation for the differential building up of species pools (more stability less extinctions).

• There is some evidence that niche conservatism at least partially drives the diversity gradients.

• Evidence for niche conservatism does not contradict alternative hypotheses, but it highlights the need for more specific predictions that enable distinction among hypotheses.

Concluding remarks