Ecological Network Resilience - Updating Projections of Ecological Networks under Optimistic and Pessimistic Scenarios of Biodiversity Loss

Abstract

Forecasting changes to ecosystem composition and functioning under climate change requires multi-species approaches that consider ecological interactions via ecological networks. 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 (the inverse of the capacity to withstand loss of links when interaction partners go extinct) and realisation of rewiring potential (the capacity to re-allocate lost interaction potential/links to novel or already established interaction partners). Using a newly developed quantitative framework, we establish simulated ecosystem projections following species-specific climate safety margin-driven extinction cascades that consider both resilience mechanisms 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. To establish a deeper understanding of the possible consequences of extinction cascades, we explore simulation outcomes according to optimistic and pessimistic network resilience assumptions as well as low- and high-emission climate change scenarios. Finally, we contrast these real-world informed extinction cascade simulation outcomes with optimistic and pessimistic baseline extinction scenarios whereby we assess the effects of removal of least- and most-connected species per network. In contrast to the traditional focus on bottom-up and top-down extinction cascades, we explore the implications of more realistic 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.