Managing for resilience through ecological structure: Examples of portfolio effects in the Great Lakes Basin

Resilient ecosystems maintain stability and function through dynamic processes like portfolio effects, wherein differential species’ responses to their environment create stability in aggregate. Portfolio effects occur within and across spatial and biological scales, creating opportunities for mobile consumers to switch resources and habitats adaptively under changing conditions. In this table, we document portfolio effects in the Great Lakes Basin, (GLB) showing that they structure resilience through adaptive capacity for a diversity of species and habitat types, with consequences that propagate through food webs from the scale of within- macrohabitats and ecosystems to coupling aquatic and terrestrial ecosystems across landscapes<i>.</i> However, our examples simultaneously demonstrate how anthropogenic perturbations and other global changes have likely eroded this adaptive capacity and therefore ecosystem resilience. Relevant definitions: <b><i>Resilience.</i></b> The capacity to <b><i>resist</i></b> perturbations, <b><i>recover</i></b> from perturbations back to its initial state, and to <b><i>reorganize</i></b> (i.e., to adapt) following perturbations to maintain functions. ‘State’ is meant broadly – it may be dynamic and preserved through dynamic processes rather than at a classically locally stable equilibrium (i.e., with all species maintaining or returning to constant density).<b><i>Portfolio effects.</i></b> Reduced <i>temporal variability</i> of an aggregate ecological function (e.g., total biomass, density, productivity, or consumption rate) compared to the variability of the individual component parts. Portfolio effects emerge due to <i>response diversity</i> among entities at any level of the biological hierarchy, from genotypes to trophic groups.<b><i>Adaptive capacity.</i></b><b><i> </i></b>The potential for a system to <i>reorganize</i> to maintain key functions. Reorganization may occur at any scale because the dynamics of smaller-scale components initiate the emergence of system-level functions that feedback to affect the component parts.Examples include not only the potential for evolutionary adaptation, but also behavioral changes, spatiotemporal re-patterning, and restructuring of carbon pathways in ecosystems.<br><br><br>