Co-ordinating Editor: Alessandro Chiarucci
Sampling procedures and species estimation: testing the effectiveness of herbarium data against vegetation sampling in an oceanic island
Article first published online: 7 JAN 2011
© 2011 International Association for Vegetation Science
Journal of Vegetation Science
Volume 22, Issue 2, pages 273–280, April 2011
How to Cite
Garcillán, P. P. and Ezcurra, E. (2011), Sampling procedures and species estimation: testing the effectiveness of herbarium data against vegetation sampling in an oceanic island. Journal of Vegetation Science, 22: 273–280. doi: 10.1111/j.1654-1103.2010.01247.x
Garcillán, P.P. (corresponding author, firstname.lastname@example.org): Centro de Investigaciones Biológicas del Noroeste (CIBNOR), Mar Bermejo 195, Col. Playa Palo de Sta. Rita, Apdo. Postal 128, La Paz, B.C.S., 23090, Mexico Ezcurra, E. (email@example.com): UC MEXUS, University of California Riverside, 900 University Ave., Riverside, CA 92521, USA
- Issue published online: 2 MAR 2011
- Article first published online: 7 JAN 2011
- Received 17 November 2008, Accepted 23 November 2010
- Guadalupe Island;
- Herbarium specimens;
- Richness estimation;
- Sampling process;
- Species-abundance distributions
Questions: What is the relationship between species assemblages in herbarium collections and species abundances in the field, and how trustworthy are herbarium data in vegetation science?
Location: Guadalupe Island, Baja California, Mexico.
Methods: We compared species-abundance distribution and evenness in 110 vegetation plots in Guadalupe Island against data from four herbaria. We tested whether the relative frequencies derived from herbarium specimens differed significantly from species frequencies in the field. We compared the rarefaction curves for both field and herbarium data sets, and tested whether taxonomic collectors accumulated new species at a higher rate than that observed in ecological plot sampling.
Results: At any given sampling effort, the total number of observed species was higher in herbarium data. The relative abundance of common species in the field was higher, and the evenness of the distribution was lower, than in herbarium data. There was no significant correlation between species abundances in the field and in the herbaria. By selectively targeting rare species, collectors accumulate previously unseen species much faster than through ecological sampling.
Conclusions: Because collectors aim for the rarer species and avoid the more common ones, the relative abundance of species in herbarium collections cannot be interpreted as a predictor of their true abundance in the field. Any statistical procedure that requires the sample to be representative of the true abundance distribution is likely to show errors when applied to herbarium data. However, because collectors actively search for rare species their rate of species accumulation is higher and their floristic lists are more complete than those obtained through ecological field sampling.