With increasing pressure placed on natural systems by growing human populations, both scientists and resource managers need a better understanding of the relationships between cumulative stress from human activities and valued ecosystem services. Societies often seek to mitigate threats to these services through largescale, costly restoration projects, such as the over one billion dollar Great Lakes Restoration Initiative currently underway. To help inform these efforts, we merged high-resolution spatial analyses of environmental stressors with mapping of ecosystem services for all five Great Lakes. Cumulative ecosystem stress is highest in nearshore habitats, but also extends offshore in Lakes Erie, Ontario, and Michigan. Variation in cumulative stress is driven largely by spatial concordance among multiple stressors, indicating the importance of considering all stressors when planning restoration activities. In addition, highly stressed areas reflect numerous different combinations of stressors rather than a single suite of problems, suggesting that a detailed understanding of the stressors needing alleviation could improve restoration planning. We also find that many important areas for fisheries and recreation are subject to high stress, indicating that ecosystem degradation could be threatening key services. Current restoration efforts have targeted high-stress sites almost exclusively, but generally without knowledge of the full range of stressors affecting these locations or differences among sites in service provisioning. Our results demonstrate that joint spatial analysis of stressors and ecosystem services can provide a critical foundation for maximizing social and ecological benefits from restoration investments.Laurentian Great Lakes | cumulative impact | marine spatial planning | fresh water

The effects of climate change on north temperate freshwater ecosystems include increasing water temperatures and decreasing ice cover. Here we compare those trends in the Laurentian Great Lakes at three spatial scales to evaluate how warming varies across the surface of these massive inland water bodies. We compiled seasonal ice cover duration and lake summer surface water temperatures (LSSWT; 1994, and analyzed spatial patterns and trends at lake-wide, lake sub-basin, and fine spatial scales and compared those to reported lake-and basin-wide trends. At the lake-wide scale we found declining ice duration and warming LSSWT patterns consistent with previous studies. At the lake sub-basin scale, our statistical models identified distinct warming trends within each lake that included significant breakpoints in ice duration for 13 sub-basins, consistent linear declines in 11 subbasins, and no trends in 4 sub-basins. At the finest scale, we found that the northern-and eastern-most portions of each Great Lake, especially in nearshore areas, have experienced faster rates of LSSWT warming and shortening ice duration than those previously reported from trends at the lake scale. We conclude that lake-level analyses mask significant spatial and

Ecological restoration programs often attempt to maintain or enhance ecosystem services (ES), but fine‐scale maps of multiple ES are rarely available to support prioritization among potential projects. Here we use agency reports, citizen science, and social media as data sources to quantify the spatial distribution of five recreational elements of cultural ES (CES) – sport fishing, recreational boating, birding, beach use, and park visitation – across North America's Laurentian Great Lakes, where current restoration investments exceed US$1.5 billion. These recreational CES are widely yet unevenly distributed, and spatial correlations among all except park visitation indicate that many locations support multiple CES benefits. Collectively, these five service metrics correlate with tourism gross domestic product, indicating that local economies benefit from ecosystem conditions that support CES. However, locations of high recreational CES delivery are often severely affected by environmental stressors, suggesting that either ecosystem condition or human enjoyment of these recreational CES is resilient even to substantial levels of stress. Our analyses show that spatial assessments of recreational CES are an informative complement to ecosystem stress assessments for guiding large‐scale restoration efforts.

The transport of water, sugar, and nutrients in trees is restricted to specific vascular pathways, and thus organs may be relatively isolated from one another (i.e. sectored). Strongly sectored leaf-to-leaf pathways have been shown for the transport of sugar and signal molecules within a shoot, but not previously for water transport. The hydraulic sectoriality of leaf-to-leaf pathways was determined for current year shoots of six temperate deciduous tree species (three ring-porous: Castanea dentata, Fraxinus americana, and Quercus rubra, and three diffuse-porous: Acer saccharum, Betula papyrifera, and Liriodendron tulipifera). Hydraulic sectoriality was determined using dye staining and a hydraulic method. In the dye method, leaf blades were removed and dye was forced into the most proximal petiole. For each petiole the vascular traces that were shared with the proximal petiole were counted. For other shoots, measurements were made of the leaf-area-specific hydraulic conductivity for the leaf-toleaf pathways (k LL ). In five out of the six species, patterns of sectoriality reflected phyllotaxy; both the sharing of vascular bundles between leaves and k LL were higher for orthostichous than non-orthostichous leaf pairs. For each species, leaf-to-leaf sectoriality was determined as the proportional differences between non-orthostichous versus orthostichous leaf pairs in their staining of shared vascular bundles and in their k LL ; for the six species these two indices of sectoriality were strongly correlated (R 2 50.94; P <0.002). Species varied 8-fold in their k LL -based sectoriality, and ringporous species were more sectored than diffuseporous species. Differential leaf-to-leaf sectoriality has implications for species-specific co-ordination of leaf gas exchange and water relations within a branch, especially during fluctuations in irradiance and water and nutrient availability.

A common prediction of evolutionary theory is that the strength of interspecific competition should decline over time among sympatric populations of competing species. Here we provide experimental evidence of historical declines in competition effects among competing zooplankton populations. Using diapausing eggs, we resurrected clones of three species of zooplankton obtained from different periods of community assembly in a single lake. We show that clones of Daphnia ambigua obtained from early in assembly when D. ambigua was dominant became extinct in competition with clones of Daphnia pulicaria and Daphnia dentifera (the current lake dominants). In contrast, D. ambigua clones obtained from later in the lake's history experienced weaker competition effects and persisted with D. dentifera. While we cannot rule out the role of intraspecific competition within D. ambigua, our results are in line with the view that natural selection favors reduced interaction strength among co-occurring species, facilitating coexistence and population persistence.

No abstract

Most ecosystems are impacted by multiple local and long-distance stressors, many of which interact in complex ways. We present a framework for prioritizing ecological restoration efforts among sites in multi-stressor landscapes. Using a simple model, we show that both the economic and sociopolitical costs of restoration will typically be lower at sites with a relatively small number of severe problems than at sites with numerous lesser problems. Based on these results, we propose using cumulative stress and evenness of stressor impact as complementary indices that together reflect key challenges of restoring a site to improved condition. To illustrate this approach, we analyze stressor evenness across the world's rivers and the Laurentian Great Lakes. This exploration reveals that evenness and cumulative stress are decoupled, enabling selection of sites where remediating a modest number of high-intensity stressors could substantially reduce cumulative stress. Just as species richness and species evenness are fundamental axes of biological diversity, we argue that cumulative stress and stressor evenness constitute fundamental axes for identifying restoration opportunities in multi-stressor landscapes. Our results highlight opportunities to boost restoration efficiency through strategic use of multi-stressor datasets to identify sites that maximize ecological response per stressor remediated. This prioritization framework can also be expanded to account for the feasibility of remediation and the expected societal benefits of restoration projects.

Ecosystems often experience multiple environmental stressors simultaneously that can differ widely in their pathways and strengths of impact. Differences in the relative impact of environmental stressors can guide restoration and management prioritization, but few studies have empirically assessed a comprehensive suite of stressors acting on a given ecosystem. To fill this gap in the Laurentian Great Lakes, where considerable restoration investments are currently underway, we used expert elicitation via a detailed online survey to develop ratings of the relative impacts of 50 potential stressors. Highlighting the multiplicity of stressors in this system, experts assessed all 50 stressors as having some impact on ecosystem condition, but ratings differed greatly among stressors. Individual stressors related to invasive and nuisance species (e.g., dreissenid mussels and ballast invasion risk) and climate change were assessed as having the greatest potential impacts. These results mark a shift away from the longstanding emphasis on nonpoint phosphorus and persistent bioaccumulative toxic substances in the Great Lakes. Differences in impact ratings among lakes and ecosystem zones were weak, and experts exhibited surprisingly high levels of agreement on the relative impacts of most stressors. Our results provide a basin-wide, quantitative summary of expert opinion on the present-day influence of all major Great Lakes stressors. The resulting ratings can facilitate prioritizing stressors to achieve management objectives in a given location, as well as providing a baseline for future stressor impact assessments in the Great Lakes and elsewhere.