CAI − Community Aggregated Index: a tool to rank and compare species assemblages combining diversity indices

Conservation science needs suitable methods for integrating different biodiversity facets to deliver cost-effective conservation strategies for threatened species and communities. In recent years, spatial comparisons based on species assemblages (e.g., communities) were performed using species richness, functional diversity, evolutionary diversity, and many other community or diversity metrics. Here, I propose using a bi-dimensional community index (e.g., Community Aggregated Index – CAI), capable of performing a multifaceted site-level prioritization, as a tool for conservation planning. CAI combines the overall sum of standardized values (named Multi Diverse Value) of taxonomic, functional, and evolutionary diversity in the first axis and the degree of uniformity (named Diversity Evenness) of the three standardized diversity values in the second axis. With these two axes, the communities characterized can be classified into a bi-dimensional space with four quadrants. In this case study, CAI was applied to identify the high-priority, penalized, and low-priority bird communities in three different habitats of Central Italy. Other diversity metrics can be used in the calculation of CAI, replacing the metrics used in this study. This bi-dimensional community index offers a versatile tool for creating comparisons among communities, with potential use to support the decision-making process in conservation planning. This information can be used to prioritize areas and allocate resources to the conservation of communities/ecosystems.