Using higher-taxon richness as a surrogate for species richness: I. Regional tests

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Abstract
Attempts to identify priority sites for conserving biodiversity are greatly hampered by a lack of good data on species' distributions. Recent work suggests one promising solution might be to use higher-level taxa (such as genera or families) which might be more easily surveyed, yet nevertheless still act as reliable surrogates for patterns of species richness. But evidence justifying this approach comes mostly from temperate datasets or inventories over enormous areas, and a number of concerns remain unanswered about the use of higher-taxon richness for identifying key conservation sites in the tropics, where most diversity occurs. Here in the first of two papers addressing these points, we explored congruence between species and higher-taxon richness across protected areas in Indo-Malaya and the Pacific rim. Our results support the use of the higher-taxon approach in guiding tropical conservation, but with certain reservations. In all three groups examined, higher-taxon richness was quite closely related to species number. However, the precision with which absolute species richness of reserves could be predicted from higher-taxon richness was often surprisingly low, particularly for rich sites where surveying higher taxa rather than species would save most time. The performance of higher taxa as surrogates also dropped sharply with increasing taxonomic rank, resulting in a trade-off between time saved by high-level surveys and the value of those surveys. Lastly, we found that species richness within individual higher taxa was potentially as powerful an indicator of the overall species diversity of a site as the number of higher taxa it contained.