Alessandro Chiarucci
University of Bologna
Rosa Maria Di Biase
DEPS, USiena
Lorenzo Fattorini
DEPS, USiena
Marzia Marcheselli
DEPS, USiena
Caterina Pisani
DEPS, USiena
Abstract
The lists of species obtained by purposive sampling by field ecologists are used to improve the sample-based estimation of species richness. The estimation criterion is a modification of the difference estimator in which the species inclusion probabilities are estimated by means of the species frequencies from incidence data. If the species list used to support the estimation is complete the estimator guesses the true richness without error. Moreover, contrary to the nonparametric estimators, our estimator provides values invariably greater than the number of species detected by the combination of sample-based and purposive surveys. A presumably asymptotically conservative estimator of the mean squared error is also provided. A simulation study based on two artificial populations is carried out in order to check the performance of the proposed estimator with respect to the familiar nonparametric estimators. Finally, the proposed estimator is adopted to estimate species richness in the Maremma Regional Park, Italy.
Keywords
Difference estimator; Probabilistic sampling; Purposive survey; Supporting list; Simulation.
Jel Codes
C13, C15, C18
