Understanding global biodiversity gradients

1. Understanding global biodiversity gradients Miguel B. Araújo Cátedra Rui Nabeiro – Biodiversidade, CIBIO, Universidade de Évora Museo Nacional de Ciências Naturales, CSIC, Madrid Gulbenkian, Lisboa, Julho 2009

2. Causes of global biodiversity gradients

3. A debate with more than 160 years Alfred Russel Wallace (1823-1913) Alexander von Humboldt (1769-1859)

4. 125 Big Questions: What we don’t know?

5. 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)

6. Framing the evolutionary hypothesis Building of the species pool - Stability Distribution of the species pool – Niche conservatism Wiens & Donoghue (2004) TREE

7. Outline • Testing for differential building up of species pool • Testing for the effects of niche conservatism • Concluding remarks

8. Test of historic climate stability hypothesis with European reptiles and amphibians Reptile species richness Simultaneous autoregressive (SAR) models used to assess spatially corrected p values between species richness and contemporary and historical climate Amphibian species richness Araújo et al. 2008 Ecography

9. Test of historic climate stability hypothesis with European reptiles and amphibians Reptile species richness Partial regression analysis to separate the unique contribution of the contemporary and historic climate variables Amphibian species richness Araújo et al. 2008 Ecography

10. Outline • Testing for differential building up of species pool • Testing for the effects of niche conservatism • Concluding remarks

11. Testing for the effects of niche conservatism – example 1 • If diversity gradients are not driven by niche conservatism, • then we would predict diversity gradients among clades originated in different periods to be similar.

12. 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.

13. 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

14. Departure from a linear relationship r=0.74 More families in the Cretaceous More families in the Tertiary Araújo et al. In preparation

15. Testing for the effects of niche conservatism – example 2 • 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.

16. 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

17. Testing for the effects of niche conservatism – example 2 Slopes from 343 studies assessing contemporary gradients of diversity for a wide range of taxa and environments Romdal, Araújo & Rahbek, In preparation

18. Outline • Testing for differential building up of species pool • Testing for the effects of niche conservatism • Concluding remarks

19. 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.