What do functional diversity, redundancy, rarity, and originality actually measure? A theoretical guide for ecologists and conservationists

Functional diversity, redundancy, rarity, and originality are fundamental concepts in ecology and conservation biology. Despite their frequent use, the precise meaning and relationships between these measures are often unclear. This paper aims to provide a comprehensive theoretical framework to elucidate what each of these measures captures and how they interrelate. By integrating traditional community-level diversity metrics with species-level specificity as used in fuzzy set theory, we bridge the gap between these concepts. Our framework reveals that while all four measures address distinct aspects of community-level and species-level functional resemblance, they can all be traced back to a common conceptual and formal framework. This theoretical guide is intended to aid ecologists and conservationists in applying these measures more effectively in their research and conservation strategies.