Assessing the completeness of bat biodiversity inventories using species accumulation curves

Abstract

Summary 1. In this study we used species accumulation models to solve one of the most serious problems encountered when comparing species richness between different communities. The problem is how to compare data among inventories in which different methodologies or measures of sampling effort have been employed. The methods used here for bats may be applied to any other biological group. We fit two asymptotic models to species accumulation curves for bat inventories to evaluate local or within‐community diversity (alpha) and landscape diversity (gamma) in central Veracruz, Mexico. 2. Species accumulation models allow us to: (i) measure within‐inventory efficacy and completeness; (ii) obtain an estimate of species richness that is based on a standardized measure of sampling effort, which makes valid comparisons between inventories possible; and (iii) estimate the minimum sampling effort required to reach a satisfactory level of completeness. 3. The applied models fit well in all cases (r2 > 0·95). The linear dependence model predicted lower asymptotes and the Clench model predicted higher asymptotes than the observed species richness. These models are useful as predictors representing the lower and upper limits between which the true species richness value should lie. 4. Alpha diversity for bats in all vegetation communities (11–18 species) was lower than the gamma diversity (20 species), suggesting that species richness and the sampling effort required are related to environmental heterogeneity. 5. We propose that 90% of the total fauna predicted by either of the models is an acceptable standardized value for comparing species richness between communities. 6. We assessed the within‐inventory completeness as the proportion of the models’ asymptote, where 90% is the desired minimum level of completeness. Except in palm stands, all bat inventories had an acceptable level of completeness, at least for the linear dependence model. 7. For conditions similar to those of our study area, the minimum effort required to obtain a satisfactory level of completeness is 5–18 nights for plant communities and 18 nights for more heterogeneous landscapes. 8. We make recommendations for improving the efficacy and completeness of bat surveys based on the application of species accumulation models.