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K.C. Burns

Is tree diversity different down-under?. K.C. Burns. The latitudinal diversity gradient: ecologies’ oldest pattern?. “Animal life is, on the whole, far more abundant and varied within the tropics...” - Alfred Russell Wallace, 1878. Alfred G. Fischer 1960. Evolution 14:64-81:.

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K.C. Burns

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  1. Is tree diversity different down-under? K.C. Burns

  2. The latitudinal diversity gradient: ecologies’ oldest pattern? “Animal life is, on the whole, far more abundant and varied within the tropics...” - Alfred Russell Wallace, 1878.

  3. Alfred G. Fischer 1960. Evolution 14:64-81: • Species richness peaks at the equator • Is species richness also higher in the southern hemisphere or ‘down-under’? • Very few tests for hemispherical asymmetries in species richness

  4. Is tree diversity higher ‘down-under’? the ‘Gentry’ database • Gentry (& colleagues) inventoried 197 forests world-wide • 0.1 ha plots (2 x 50 m transects, n=10 per site) • all woody plants > 2.5 cm DBH were identified • species were classified as a tree, liana or hemi-epiphyte. • variables: population density and species richness • http://www.mobot.org/MOBOT/research/gentry/data.shtml and in detail by Phillips & Miller (2002).

  5. Tree species richness per unit area is higher down-under

  6. Confounding effects? Sampling asymmetry – there are more high latitude samples in the northern hemisphere

  7. Confounding effects Do geographic differences in sampling intensity influence results?

  8. Otari-Wilton's Bush

  9. Otari-Wilton's Bush

  10. Confounding effects Are patterns sensitive to plant growth form?

  11. Confounding effects Is there variation in ‘insularity’ between hemispheres?

  12. Do hemispherical asymmetries persist after controlling for potential confounds? Results remain unchanged after: 1. Including the New Zealand site and restricting analyses to sites < 42° latitude. 2. Removing insular sites. 3. Restricting analyses to North and South America 4. Analysing trees and climbing plants (lianas & hemi-epiphytes) separately

  13. How do tree abundances vary with latitude? How are patterns in species richness per unit area influenced by variation in tree abundances?

  14. population density Should species richness be measured on a per area basis or a per individual basis?

  15. “Standardizing datasets by area may produce very different results compared to standardizing by the number of individuals collected, and it is not always clear which measure of diversity is more appropriate” - Gotelli & Colwell, 2001

  16. How could you account for latitudinal changes in tree densities?

  17. After controlling for sampling effects, the direction of hemispherical diversity asymmetries reverses • On a per-individual basis tree diversity is higher in the northern hemisphere

  18. Conclusions - Otari-Wilton’s Bush Vancouver island, Canada • Tree diversity differs between hemispheres • However, identifying which hemisphere is more diverse hinges on one’s perspective on how species diversity should be defined

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