Updating Projections of Ecological Networks by Integrating Co-Extinction Resilience Mechanisms

Abstract

While ecosystem projections have previously been made using ecological network approaches, mainly focusing on extinction cascade directionality as a driving force of ecological change, only a few studies have explicitly considered resilience mechanisms of ecological networks towards species extinctions. These mechanisms are link-loss sensitivity (i.e., the inverse of the capacity to withstand loss of links when interaction partners go extinct) and realisation of rewiring potential (i.e., the capacity to re-allocate lost interaction potential/links to novel or already established interaction partners). We have developed a quantitative framework with which to do so and subsequently established simulated ecosystem projections following species-specific climate safety margin-driven extinction cascades that consider both resilience mechanisms as well as cascade directionality across an array of globally-distributed in-situ sampled mutualistic networks. To identify the effects of network resilience mechanisms on loss of biodiversity and change in connectedness, our approach explicitly explores two-dimensional resilience landscapes defined by link loss sensitivity and realisation of rewiring potential. In addition to the traditional focus on bottom-up and top-down extinction cascades, we also explore the implications of bi-directional extinction cascades. Our results indicate that neglecting to account for ecological network resilience mechanisms may lead to severe underpredictions of ecological change measured as loss of biodiversity and change in connectedness. We also find that increasing link-loss sensitivity results in far greater numbers of secondary extinctions, while increases in rewiring potential abate secondary extinctions. Furthermore, we find that the contemporary focus on differences between bottom-up and top-down outcomes may obscure the considerably larger risk of biodiversity loss posed through bidirectional extinction cascades.