PARENT SESSION
Poster Session 19: Biodiversity
Wednesday, August 10, 5:00 PM - 6:30 PM, Exhibit Hall 220 A-E, Level 2, Palais des congrès de Montréal

Estimating plant species richness in Guadalupe island, Mexico, using species accumulation curves and non-parametric methods.

P. Garcillan, Pedro^*,1, Vega, Ernesto², ¹ CICESE, Ensenada, Baja California, Mexico² Instituto Nacional de Ecologia, Mexico DF, Mexico

ABSTRACT- Guadalupe is an oceanic island of about 250 km² located approximately 260 km off the coast of Baja California peninsula in Mexico and it is considered and outlier from the California Floristic Province. After almost two hundred years of intense presence of goats on the island, the native flora and plant communities have been devastated. A total of 170 native plant species have been documented on the island, and it has been estimated that at least 26 species could be extinct. Furthermore, the population size of many other species has been dramatically reduced, and about 50 exotic plant taxa have been recorded on the island. At present, there is a program to eradicate the goats from the island and to diagnose the island ecological status. The first step for this diagnosis was to estimate the plant species richness in Guadalupe Island. We used several species richness estimation methods using field data collected in spring 2004 and compared their results to the initial 194 plant species previously documented. We divided the island in 45 cells of 1.5' Latitude by 1.5' Longitude, and made on average three transects in each cell. A total of 110 transects (50m x 2m) along the island were surveyed and all vascular plant species were registered for each transect. A total of 80 species were found, 50 of them were native species and the other 30 were non native species. We estimated the total species number through three different species accumulation models: a) the linear dependence model, b) the Clench model, and c) the T-S curve (a semi log model with a successive addition of predefined subsets of samples); and three non-parametric methods: a) Chao 2, b) Jacknife 2, and c) ICE. Preliminary results show that extrapolation of the traditional species-accumulation models, the linear and Clench models, (75 and 84 species respectively) and application of non-parametric methods (89, 89 and 98 species, respectively) gave large underestimates compared with the initial 194 of species documented in the island. Extrapolation of the T-S curve gave a significantly closer estimation (178 species) of the initial 194 species. The explication of that may be that the high spatial heterogeneity of the island is better captured by the T-S curve.

Key words: biodiversity, species accumulation curves, nonparametric estimators, Guadalupe island