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Generation of Earth's first-order biodiversity pattern.
Andrew Z Krug1, David Jablonski, James W Valentine
1Department of Geophysical Sciences, University of Chicago, Chicago, Illinois, USA. akrug@uchicago.edu
Astrobiology
|February 14, 2009
Summary
The latitudinal diversity gradient (LDG) shows species richness decreases from equator to poles. Fossil bivalves reveal that origination and range expansion, primarily from the tropics, drive this pattern, not just extinction rates.
Area of Science:
- Paleontology
- Biodiversity Science
- Evolutionary Biology
Background:
- The latitudinal diversity gradient (LDG) describes decreasing species richness from the equator to the poles, a pattern observed from the present day back to the Paleozoic.
- Understanding the evolutionary processes (origination, extinction, dispersal) driving the LDG is crucial, as static pattern analyses are insufficient.
Purpose of the Study:
- To investigate the role of origination, extinction, and dispersal in generating the latitudinal diversity gradient using the marine bivalve fossil record.
Main Methods:
- Analysis of the marine bivalve fossil record to examine biodiversity dynamics over large temporal and spatial scales.
- Investigating geographic trends in species origination, extinction, and range expansion in relation to latitude.
Main Results:
- Origination rates and peak diversities are highest in the tropics, with range expansion predominantly occurring out of the tropics.
- This origination-diversity link holds even for a group with a mid-latitude diversity peak, highlighting the importance of spatial origination variations.
- Lower extinction rates at polar latitudes do not solely explain the LDG; they may contribute to damped origination and immigration.
Conclusions:
- Spatial variations in origination, particularly range expansion from the tropics, are a primary driver of the latitudinal diversity gradient.
- Resource availability and seasonality may influence origination and adaptation in higher latitudes, favoring generalist species.
- Lineage spread, driven by speciation, predominantly occurs poleward when resources become available due to extinctions.
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