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Lakes and ponds experience anthropogenically forced changes that may be non-linear and sometimes initiate ecosystem feedbacks leading to tipping points beyond which impacts become hard to reverse. In many cases climate change is a key driver, sometimes in concert with other stressors. Lakes are also important players in the global climate by ventilating a large share of terrestrial carbon (C) back to the atmosphere as greenhouse gases and will likely provide substantial feedbacks to climate change. In this paper we address various major changes in lake ecosystems and discuss if tipping points can be identified, predicted, or prevented, as well as the drivers and feedbacks associated with climate change. We focus on potential large-scale effects with regional or widespread impacts, such as eutrophication-driven anoxia and internal phosphorus (P) loading, increased loading of organic matter from terrestrial to lake ecosystems (lake “browning”), lake formation or disappearance in response to cryosphere shifts or changes in precipitation to evaporation ratios, switching from nitrogen to phosphorus limitation, salinization, and the spread of invasive species where threshold-type shifts occur. We identify systems and drivers that could lead to self-sustaining feedbacks, abrupt changes, and some degree of resilience, as opposed to binary states not subject to self-propelling changes or resilience. Changes driven by warming, browning, and eutrophication can cause increased lake stratification, heterotrophy (browning), and phytoplankton or macrophyte mass (eutrophication), which separately or collectively drive benthic oxygen depletion and internal phosphorus loading and in turn increase greenhouse gas (GHG) emissions. Several of these processes can feature potential tipping point thresholds, which further warming will likely make easier to surpass. We argue that the full importance of the vulnerability of lakes to climate and other anthropogenic impacts, as well as their fe

The COVID-19 pandemic has reflected our failures and successes as global society in responding to crises, particularly regarding food insecurity. Responses varied greatly around the world. Here, we aimed to identify and compare the government and civil society’s responses to food insecurity and hunger during the pandemic in Montevideo, Uruguay and Wisconsin, USA. We analysed official data on hunger and hunger alleviation strategies and conducted a series of interviews with several Uruguayan and American stakeholders, from NGOs, grassroot organizations, and governmental officers, among other social actors. We also conducted online surveys addressed to Uruguayan consumers and farmers which were answered by over 750 people in the first months of the pandemic. Our analysis and narrative therefore builds on a mixture of qualitative and quantitative data. We enriched our analysis with a series of lived experiences that provided better insights into the feelings, actions and perceptions recorded in the interviews and surveys. We highlight different response strategies (largely top-down in Wisconsin, and a mix of top-down and bottom-up in Montevideo), discuss some of their successes and failures, compare official and popular narratives, and reflect on potential changes to be made to help shape more resilient local food systems but also to enhance the resilience and dignity of communities facing hunger.

This chapter assesses scientific evidence for tipping points across the biosphere, which comprises Earth’s ecosystems. Human-driven habitat loss, pollution, exploitation and, increasingly, climate change are degrading ecosystems across the planet, some of which can pass tipping points beyond which a ‘regime shift’ to an alternative (and often less diverse or beneficial) ecosystem state occurs.Evidence for tipping points emerges across many biomes. In forests,large parts of the Amazon rain forest could tip to degraded forest or impoverished savanna, while tipping in boreal forests is possible but more uncertain, and whether current temperate forest disturbance could lead to tipping is unclear. In open savannas and drylands,drying could lead to desertification in some areas, while in others encroachment by trees and shrubs could see these biodiverse ecosystems shift to a forested or degraded state. Nutrient pollution and warming can trigger lakes to switch to an algae-dominated low-oxygen state. Coral reefs are already experiencing tipping points, as more frequent warming-driven bleaching events, along with pollution,extreme weather events and diseases, tip them to degraded algae-dominated states. Mangroves and sea grasses are at risk of regional tipping, along with kelp forests, marine food webs and some fisheries,which are known to be able to collapse.Together, these tipping points threaten the livelihoods of millions of people, and some thresholds are likely imminent. Stabilising climate is critical for reducing the likelihood of widespread ecosystem tipping points, but tackling other pressures can also help increase ecological resilience, push back tipping and support human well being.

The wicked nature of sustainability challenges facing food systems demands intentional and synergistic actions at multiple scales and sectors. The Southern Cone of Latin America, with its historical legacy of “feeding the world,” presents interesting opportunities for generating insights into potential trajectories and processes for food system transformation. To foster such changes would require the development of collective understanding and agency to effectively realize purposeful and well-informed action toward desirable and sustainable food futures. This in turn demands the transdisciplinary engagement of academia, the private sector, government/policy-makers, community groups, and other institutions, as well as the broader society as food consumers. While the need for contextualized knowledge, priorities and definitions of what sustainable food systems change means is recognized, there is limited literature reporting these differences and critically reflecting on the role of knowledge brokers in knowledge co-production processes. The political nature of these issues requires arenas for dialogue and learning that are cross-sectoral and transcend knowledge generation. This paper presents a case study developed by SARAS Institute, a bridging organization based in Uruguay. This international community of practice co-designed a 3-year multi-stakeholder transdisciplinary process entitled “Knowledges on the Table.” We describe how the process was designed, structured, and facilitated around three phases, two analytical levels and through principles of knowledge co-production. The case study and its insights offer a model that could be useful to inform similar processes led by transdisciplinary communities of practice or bridging institutions in the early stages of transformative work. In itself, it also represents a unique approach to generate a language of collaboration, dialogue, and imagination informed by design skills and methods. While this is part of a longer

Body size is a fundamental attribute of organisms because many physiological rates are size-dependent. Body size also determines ecological structures and processes including population abundance, predator-prey interactions and the resilience capacity of the food webs. Thus, the natural variations in community size structure can potentially have profound effects on ecosystem functioning. Most of the empirical studies about the size structure of aquatic communities have focused on marine ecosystems, but more recently on lentic ecosystems. Studies about the community size structure in rivers are scarce and mainly focus on simple size- related variables such as the mean or maximum length of organisms. Thus, there is still great potential to test the use of other size-related variables (i.e., size spectra, size diversity) as ecological indicators of river fish communities. The abundance size spectrum describes the log-log relationship between body size and abundance, typically with abundance summed within size bins of geometric series of two. The size diversity integrates the amplitude of the size range and the evenness across size in the same way as the Shannon species diversity integrates the number of species and their relative abundance. We have recently conducted several projects to test the main drivers shaping these size-related variables on fish communities in rivers and streams. In the Andes (Peru and Colombia) we identified systematic changes of the fish size structure along the altitudinal gradient on streams with pristine conditions. In subtropical streams (Uruguay) we detected that fish size community structure changed along a gradient of land uses, from more anthropogenic disturbed basins (i.e., the dominance of urban and agricultural land use) to more pristine stream basins (i.e., the dominance of rangelands). In Mediterranean streams (Spain) we also showed that the size structure of fish community consistently responded to the local water conditions and