Appendix H. Prevalence of co-occurring congeners: the Gentry data set.
The Gentry data set comprises 226 files each containing a list of all woody individuals within 10, 2 m × 50 m transects, with files representing different sites around the world. For 91 of these files we checked species identity against voucher numbers for each individual and where possible corrected any unknowns and misidentifications. In any one file, between 50100% of samples from unknowns were still awaiting herbarium identification. For several files we found an apparent overall mismatch between voucher numbers and site; corrections were not possible and these files were not included in the final analysis. Within usable files, 515% of field identifications were incorrect. Unknown genera were field designated as M1, M2…etc., on a file by file basis. Unknown species were treated in the same way. For our estimation of percent congeners, we included uncorrected unknowns, assuming the designations of unknowns accurately reflected genus membership.
For the 91 files from 84 sites (13 in Africa, 5 in Europe, 23 in MesoAmerica, 27 in temperate North America and 16 in tropical Asia), we found that on average, 29% of the species within a file were congeners (SE = 2.30). Note that the calculation excludes Gentry’s family-rich South American transects, due to the high percentage of as yet unidentified unknowns in those files. The relatively small area sampled by the Gentry data will be less likely to include rarer species. As an indicator of this effect, percent congeners in the four sets of transects in the Gentry data assayed in the Chamela forest (the site of the study reported in Kelly et al. 2001, Kelly and Bowler 2002) ranged from 21 to 36% of the species in each 1 ha of a set of transects; in contrast, the 3.4 ha encompassed in the permanent plots at that site in which all woody individuals have been identified (described in Kelly et al. 2001, Kelly and Bowler 2002) contains 45% congeners. Amalgamation of Gentry’s four Chamela files shows 42.5% congeners. Amalgamation of file pairs from four other sites in the Gentry files also gave higher estimates of congener co-occurrence than either plot set by itself.
Kelly, C. K., H. Banyard Smith, Y. M. Buckley, R. Carter, M. Franco, W. Johnson, T. Jones, B. May, R. Perez Ishiwara, A. Perez-Jimenez, A. Solis Magallanes, H. Steers, and C. Waterman. 2001. Investigations in commonness and rarity: a comparative analysis of co-occuring, congeneric Mexican trees. Ecology Letters 4:618627.
Kelly, C. K., and M. G. Bowler. 2002. Coexistence and relative abundance in forest tree species. Nature 417:437440.