Search

Understanding the interactions among anthropogenic stressors is critical for effective conservation and management of ecosystems. Freshwater scientists have invested considerable resources in conducting factorial experiments to disentangle stressor interactions by testing their individual and combined effects. However, the diversity of stressors and systems studied has hindered previous syntheses of this body of research. To overcome this challenge, we used a novel machine learning framework to identify relevant studies from over 235,000 publications. Our synthesis resulted in a new dataset of 2396 multiple‐stressor experiments in freshwater systems. By summarizing the methods used in these studies, quantifying trends in the popularity of the investigated stressors, and performing co‐occurrence analysis, we produce the most comprehensive overview of this diverse field of research to date. We provide both a taxonomy grouping the 909 investigated stressors into 31 classes and an open‐source and interactive version of the dataset (https://jamesaorr.shinyapps.io/freshwater‐multiple‐stressors/). Inspired by our results, we provide a framework to help clarify whether statistical interactions detected by factorial experiments align with stressor interactions of interest, and we outline general guidelines for the design of multiple‐stressor experiments relevant to any system. We conclude by highlighting the research directions required to better understand freshwater ecosystems facing multiple stressors. [ABSTRACT FROM AUTHOR]

Catastrophic state changes often occur in ecosystems as consequences of shifts in the dominant life forms, such as in the case of sportfish introduction into naturally fishless mountain lakes. While the pronounced ecological displacement of native communities by these novel predators (i.e., weak resistance) is well documented, few studies have also examined the dynamics of their recovery rates (i.e., "engineering resilience") following stressor removal. We addressed this knowledge gap by quantifying the taxonomic and species trait‐based ordination trajectories of crustacean zooplankton communities in stocked alpine lakes, which differed in how they were restored to a natural fishless state over a period of six decades. Resilience and resistance trajectories differed in each lake as the ecological importance of trait‐based species recolonization potential (e.g., asexual vs. sexual reproduction) replaced that of tolerance of size‐selective predation by fish (e.g., body size, pigmentation, motility). As a result, re‐establishment of large‐bodied zooplankton following the elimination of fish restored annual secondary production. In contrast, a more gradual unidirectional ordination trajectory toward smaller zooplankton body size and a decline in total zooplankton biomass occurred in a nearby alpine lake containing a protected native bull trout population. Although recovery trajectories returned via routes that differed from those of earlier resistance trajectories (i.e., hysteresis), we discovered that full taxonomic and functional recovery was realized in all the restored fishless lakes within three decades, regardless of the approach used to achieve ecosystem restoration. [ABSTRACT FROM AUTHOR]