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| Databases on the distribution of species can be used to describe the geographic patterns of biodiversity.
Nevertheless, they have limitations. We studied three of these limitations: (1) inadequacy of raw
data to describe richness patterns due to sampling bias, (2) lack of survey effort assessment (and lack of
exhaustiveness in compiling data about survey effort), and (3) lack of coverage of the geographic and environmental
variations that affect the distribution of organisms. We used a biodiversity database (BIOTA-Canarias)
to analyze richness data from a well-known group (seed plants) in an intensively surveyed area (Tenerife
Island). Observed richness and survey effort were highly correlated. Species accumulation curves could not be
used to determine survey effort because data digitalization was not exhaustive, so we identified well-sampled
sites based on observed richness to sampling effort ratios. We also developed a predictive model based on the
data from well-sampled sites and analyzed the origin of the geographic errors in the obtained extrapolation
by means of a geographically constrained cross-validation. The spatial patterns of seed-plant species richness
obtained from BIOTA-Canarias data were incomplete and biased. Therefore, some improvements are needed
to use this database (and many others) in biodiversity studies. We propose a protocol that includes controls
on data quality, improvements on data digitalization and survey design to improve data quality, and some
alternative data analysis strategies that will provide a reliable picture of biodiversity patterns. | |
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