Prioritizing site groups for intrinsic biodiversity assets using complementarity and not just rarity

Conservation practitioners rightfully focus on at‐risk species when valuing biodiversity assets and prioritizing spatial units. However, sites often contain few if any of those species, making valuation and prioritization difficult. A complementarity approach that incorporates broader community information may strengthen the assessment, yet empirical demonstrations centered on comparing and combining at‐risk species with other metrics appear to be lacking. We compared and combined numbers of at‐risk species with four other community metrics using surveys of vascular plants at wetlands in a preserve network (Illinois, USA). Out of 247 species observed, only one was listed by Illinois for legal protection and six others as Illinois “imperiled.” Many sites lacked these species or shared equal numbers of at‐risk species (including the 49 with Illinois “vulnerable” status), limiting the ability to differentiate and prioritize the sites. Yet numbers of at‐risk species still contributed to the complementarity of taxonomic, functional, and phylogenetic diversity information. This complementarity enabled identifying an intrinsically valuable site group, plus alternative groupings, and highlights a set of simple metrics to apply for site prioritizations.