Systematic, large-scale national biodiversity surveys: NeoMaps as a model for tropical regions

Aim: To test a method for rapidly and reliably collecting species distribution and abundance data over large tropical areas [known as Neotropical Biodiversity Mapping Initiative (NeoMaps)], explicitly seeking to improve cost- and time-efficiencies over existing methods (i.e. museum collections, literature), while strengthening local capacity for data collection. Location: Venezuela. Methods: We placed a grid over Venezuela (0.5 × 0.5 degree cells) and applied a stratified sampling design to select a minimum set of 25 cells spanning environmental and biogeographical variation. We implemented standardized field sampling protocols for birds, butterflies and dung beetles, along transects on environmental gradients ('gradsects'). We compared species richness estimates from our field surveys at national, bioregional and cell scales to those calculated from data compiled from museum collections and the literature. We estimated the variance in richness, composition, relative abundance and diversity between gradsects that could be explained by environmental and biogeographical variables. We also estimated total survey effort and cost. Results: In one field season, we covered 8% of the country and recorded 66% of all known Venezuelan dung beetles, 52% of Pierid butterflies and 37% of birds. Environmental variables explained 27—60% of variation in richness for all groups and 13—43% of variation in abundance and diversity in dung beetles and birds. Bioregional and environmental variables explained 43—58% of the variation in the dissimilarity matrix between transects for all groups. Main conclusions: NeoMaps provides reliable estimates of richness, composition and relative abundance, required for rigorous monitoring and spatial prediction. NeoMaps requires a substantial investment, but is highly efficient, achieving survey goals for each group with 1-month fieldwork and about US$ 1—8 per km 2 . Future work should focus on other advantages of this type of survey, including the ability to monitor the changes in relative abundance and turnover in species composition, and thus overall diversity patterns.