How the equilibrium assumption is addressed in empirical tests of major ecological theories

The idea that natural systems tend to be at equilibrium dates back to the
origin of the field of ecology and continues to underlie most ecological
theory. However, empirical evidence for equilibrium dynamics in nature and
in experiments is surprisingly elusive. Here, we address this conundrum by
first exploring the history of equilibrium in ecological theory and the
evidence for equilibrium dynamics in natural systems. We then search the
literature to quantify how empiricists deal with equilibrium in their
research, and we address barriers to integrating equilibrium into
empirical work by providing step-by-step instructions for determining
whether a population is at equilibrium. Next, we lay out three ways that
equilibrium is embedded in theory, and for each, outline when meeting the
equilibrium assumption in empirical tests is critical for scientific
inference, and when it is possible to relax this assumption. And finally,
we present concrete steps that empiricists and theoreticians can each take
in order to meet in the middle when it comes to equilibrium. We hope that
this paper will stimulate new discussions from researchers from across the
theory-empirical divide about this longstanding issue.