How do Empirical Metacommunity Ecologists (not) Define Local Communities and How Could These be Better Defined?

Metacommunity Theory is among the most widely used theoretical frameworks in empirical community ecology. A central assumption of this framework is that individuals are structured into local communities, which collectively form the metacommunity. Thus, the concept of the local community is fundamental for connecting empirical observations with theoretical predictions. However, through a literature review, we show that most empirical studies conceptualised within Metacommunity Theory lack explicit spatial definitions of local communities. Among those that do, few provide ecological justification. We argue that this mismatch between theoretical assumptions and empirical practice hinders the interpretability and comparability of empirical results. To address this gap, we propose three alternative approaches for delineating local communities. These are based on whether conspecific and heterospecific individuals overlap in their space-use, interact with each other or have reciprocal fitness effects. Using agent-based simulations, we show how these three definitions may result in different delineations of local communities and that local communities do not necessarily form discrete units. To align empirical studies with Metacommunity Theory, we urge ecologists to explicitly define what spatial units they conceptualise as local communities. We also offer guidelines on what complementary data could be collected to achieve ecologically justified delineations of local communities.