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): Jim USDA-NRCS PLANTS Database

Vellend 2003: Results from 14 island studies THE SGDC 1.Correlation not Causation 2.Is there a common process (X)? 3.Vellend 2004: Recovering forest herb communities… X = drift…

Vellend 2004: Methods turehttp://en.wikipedia.org/wiki/Agricul ture 10 1° (untouched) 17 2° (abandoned pastures) Sites Vellend usa.com/usgsentry.aspx?T=2&S=16&Z=18&X=29&Y=366&W=1&qs=%7cTom pkins+County%7cNew+York%7c Characteristics of each site: 1.Trillium grandiflorum 2.Isolated 3.Similar Soil Associations Tompkins County NY

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

How SD & GD might change in parallel… 1° > 2°1° < 2° SD & GD DiversityDivergence Within site… Between site…

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

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

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

Other factors: (ii) Soil Heterogeneity Selection explains greater divergences in abundances between sites as well as drift… 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? Fst-C Greater divergence in abundances between 2° sites

Other factors: (iii) Hedge Rows as source populations? Included only 3 as 1° sites Corbit et al (1998) finds them to be important source populations for surrounding forest

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

Other factors: (iii) hedge rows: Migration explains lower divergence in species types in 2° stands as well as selection? Brc

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

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

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? l.html