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The SGDC pattern in recovering forest herb communities: Explained by drift?

Jim Stasz @ USDA-NRCS PLANTS Database. The SGDC pattern in recovering forest herb communities: Explained by drift?. Critique: Vellend, Mark (2004) Parallel effects of land-use history on species diversity and genetic diversity of forest herbs. Ecology 85(11): 3043-3055.

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The SGDC pattern in recovering forest herb communities: Explained by drift?

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  1. Jim Stasz @ USDA-NRCS PLANTS Database The SGDC pattern in recovering forest herb communities:Explained by drift? Critique: Vellend, Mark (2004) Parallel effects of land-use history on species diversity and genetic diversity of forest herbs. Ecology 85(11): 3043-3055

  2. Vellend 2003: Results from 14 island studiesTHE SGDC • Correlation not Causation • Is there a common process (X)? • Vellend 2004: Recovering forest herb communities… X = drift…

  3. Vellend 2004:Methods • http://en.wikipedia.org/wiki/Agriculture 10 1° (untouched) Characteristics of each site: Trillium grandiflorum Isolated Similar Soil Associations Tompkins County NY Vellend 2005 Sites 17 2° (abandoned pastures) http://www.pbs.org/wnet/nature/holycow/images/top_pic2d.jpg http://terraserver-usa.com/usgsentry.aspx?T=2&S=16&Z=18&X=29&Y=366&W=1&qs=%7cTompkins+County%7cNew+York%7c

  4. For each 1º & 2º site measured… Community Species of Forest Herbs Genetic (T. grandiflorum) Within site (Diversity) Between Sites (Divergence) SR E AR He Brc Fst-C Fst-G Drift? Selection?

  5. How SD & GD might change in parallel… 1° > 2° SD & GD SD & GD Diversity Divergence 1° < 2° Between site… Within site…

  6. In general, Vellend found the SGDC… ….but was this pattern primarily caused by drift? Factorsbest at explaining variance, were indicators ofdrift: Land-use history (1 vs. 2)** Population size** Area** Other factors: pH Habitat Isolation Environmental heterogeneity BUT not all the variance is explained by these factors… Missing factors? ** They contributed the most to the ‘full model’

  7. Other factors:(i) Biotic environment! Vellend 2005 results… Controlled all abiotic factors… Still a difference! Selection? Contradiction to 2004: drift… x lots… x few… Herbivore behaviour? 1° 2° Competition with other plants? • Only measured native forest herbs! • Invasive species? • Remnant open-field species? Tompkins county overrun with deer… vs. local bookstores.. http://efl.htmlplanet.com/xmas_songs.htm

  8. Other Factors: (i) Biotic:Selection explains lower abundances in 2º sites as well asdrift? Lower abundances in 2º sites E

  9. Other factors:(ii) Soil Heterogeneity 20 Soil Samples from each site, mixed together to get an average. No measure of within site variance! More patchy distribution of species in 2º sites? Selectionexplains greater divergences in abundances between sites as well asdrift… Greater divergence in abundances between 2° sites Fst-C

  10. Other factors:(iii) Hedge Rows as source populations? Includedonly 3as 1° sites Corbit et al (1998) finds them to beimportant source populationsfor surrounding forest http://www.jaynecotten.com/images4/hedge1.jpg

  11. Other factors:(iii) Hedge Rows as source populations? 1° Sites 2° Sites Most common forest herbs in hedge, same in 2 ° and 1°.

  12. Other factors: (iii) hedge rows:Migrationexplains lower divergence in species types in 2° stands as well asselection? Brc

  13. Is Drift the main process? Vellend interpretations: SR E AR He Brc Fst-C Fst-G Drift? Selection? Further interpretations: SR E AR He Brc Fst-C Fst-G Drift? Selection? Migration?

  14. 1° > 2° So, still see SGDC pattern… but as for a common process… SD & GD SD & GD Diversity Divergence 1° < 2° X=?

  15. A few more comments… • Applications… • Only to isolated secondary stands • Only to forest herb communities • Only with history of pasturing • Non-equilibrial community? • Supports SGDC pattern • Unification of community and genetic disciplines… • E.g. Hubbell’s ecological drift parallels genetic drift… • Common process to SGDC pattern? • More studies… • Oversimplification of model? http://www.news.cornell.edu/Chronicle/03/9.11.03/deer_dispersal.html

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