From metrics to meaning: diversity as an essentially contested concept

Jonathan A Newman, Pedro R. Peres-Neto

Biodiversity is among ecology’s most widely invoked but least consistently defined concepts. Despite decades of theoretical and methodological developments, ecologists continue to disagree about what "diversity" measures and how it should be quantified. These disagreements have direct consequences to conservation science, policy making, and public engagement. We argue that this enduring debate is not a sign of conceptual failure but evidence that "diversity" is an "essentially contested concept" (ECC) sensu Gallie (1955). Diversity is internally complex, appraisive, and historically dynamic: it comprises multiple, value-laden dimensions whose relative importance depends on context and purpose. Using examples from taxonomic diversity, we show that common metrics (e.g., richness, Shannon, Simpson, and Hill numbers) encode distinct value judgments (normative commitments) about how abundances shape diversity and, in turn, determine which species are considered most important to biodiversity. Likewise, spatial frameworks such as additive and multiplicative partitioning embody different normative assumptions about whether diversity represents the sum of local contributions or the relationships among communities. Beyond metrics, both definitional ambiguity and persistent knowledge shortfalls reinforce diversity’s plural and evolving character. Our goal is to show that recognizing diversity as an ECC is not a weakness of ecological thought, but rather a call for more reflective, inclusive, responsible research, teaching, and policy, anchoring biodiversity science within a richer understanding of its ethical and epistemic foundations. Diversity’s very "elusiveness" is what makes it powerful: it invites ecologists, policymakers, and citizens alike to reflect on what they value in the living world and to be explicit about how those values shape science and decision-making. Recognizing biodiversity as an ECC reframes disagreement as an opportunity rather than an obstacle. It calls for transparency about normative commitments, pluralism in measurement, and reflexivity in linking ecological analysis to ethical and political goals. Treating diversity as an ECC clarifies why no single metric can be definitive and offers a principled foundation for navigating conceptual plurality across ecological research, conservation planning, and global biodiversity governance.