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The powerful community-structuring roles of foundation species (FS) are well recognized; however, ecological interactions involving their dead structures have yet to be broadly integrated within ecological theory or ecosystem management. As interacting components of ecosystems, dead foundation species (DFS) modify environments and mediate feedbacks underpinning ecosystem resilience. DFS are vulnerable to global change and often respond differently than living FS. Changes in DFS quantity, composition, and frequency of occurrence influence habitat heterogeneity within systems and subsidy dynamics across systems, provoking far-reaching effects on biodiversity and ecosystem functions. Enhanced recognition of DFS traits and ecological roles will improve restoration outcomes, inform ecological forecasts, and guide conservation of ecosystems challenged by global change. Foundation species facilitate communities, modulate energy flow, and define ecosystems, but their ecological roles after death are frequently overlooked. Here, we reveal the widespread importance of their dead structures as unique, interacting components of ecosystems that are vulnerable to global change. Key metabolic activity, mobility, and morphology traits of foundation species either change or persist after death with important consequences for ecosystem functions, biodiversity, and subsidy dynamics. Dead foundation species frequently mediate ecosystem stability, resilience, and transitions, often through feedbacks, and harnessing their structural and trophic roles can improve restoration outcomes. Enhanced recognition of dead foundation species and their incorporation into habitat monitoring, ecological theory, and ecosystem forecasting can help solve the escalating conservation challenges of the Anthropocene. Foundation species facilitate communities, modulate energy flow, and define ecosystems, but their ecological roles after death are frequently overlooked. Here, we reveal the widespread importance of their dead structures as unique, interacting components of ecosystems that are vulnerable to global change. Key metabolic activity, mobility, and morphology traits of foundation species can either change or persist after death with important consequences for ecosystem function, biodiversity, and subsidy dynamics. Dead foundation species frequently mediate ecosystem stability, resilience, and transitions, often through feedbacks, and harnessing their structural and trophic roles can improve restoration outcomes. Enhanced recognition of dead foundation species and their incorporation into habitat monitoring, ecological theory, and ecosystem forecasting can help solve the escalating conservation problems of the Anthropocene. [ABSTRACT FROM AUTHOR]

Habitat heterogeneity is considered a primary causal driver underpinning patterns of diversity, yet the universal role of heterogeneity in structuring biodiversity is unclear due to a lack of coordinated experiments testing its effects across geographic scales and habitat types. Furthermore, key species interactions that can enhance heterogeneity, such as facilitation cascades of foundation species, have been largely overlooked in general biodiversity models. Here, we performed 22 geographically distributed experiments in different ecosystems and biogeographical regions to assess the extent to which variation in biodiversity is explained by three axes of habitat heterogeneity: the amount of habitat, its morphological complexity, and capacity to provide ecological resources (e.g. food) within and between co-occurring foundation species. We show that positive and additive effects across the three axes of heterogeneity are common, providing a compelling mechanistic insight into the universal importance of habitat heterogeneity in promoting biodiversity via cascades of facilitative interactions. Because many aspects of habitat heterogeneity can be controlled through restoration and management interventions, our findings are directly relevant to biodiversity conservation. Species interactions that can enhance habitat heterogeneity such as facilitation cascades of foundation species have been overlooked in biodiversity models. This study conducted 22 geographically distributed experiments in different ecosystems and biogeographical regions to assess the extent to which biodiversity is explained by three axes of habitat heterogeneity in facilitation cascades. [ABSTRACT FROM AUTHOR]

Many wetlands around the world that occur at the base of watersheds are under threat from land‐use change, hydrological alteration, nutrient pollution, and invasive species. A relevant measure of whether the ecological character of these ecosystems has changed is the species diversity of wetland‐dependent waterbirds, especially those of conservation value. Here, we evaluate the potential mechanisms controlling variability over time and space in avian species diversity of the wetlands in the Palo Verde National Park, a Ramsar Site of international importance in Costa Rica. To do so, we assessed the relative importance of several key wetland condition metrics (i.e., surface water depth, wetland extent, and vegetation greenness), and temporal fluctuations in these metrics, in predicting the abundance of five waterbirds of high conservation value as well as overall waterbird diversity over a 9‐yr period. Generalized additive models revealed that mean NDVI, an indicator of vegetation greenness, combined with a metric used to evaluate temporal fluctuations in the wetland extent best predicted four of the five waterbird species of high conservation value as well as overall waterbird species richness and diversity. Black‐bellied Whistling‐ducks, which account for over one‐half of all waterbird individuals, and all waterbird species together were better predicted by including surface water depth along with wetland extent and its fluctuations. Our calibrated species distribution model confidently quantified monthly averages of the predicted total waterbird abundances in seven of the 10 sub‐wetlands making up the Ramsar Site and confirmed that the biophysical diversity of this entire wetland system is important to supporting waterbird populations both as a seasonal refuge and more permanently. This work further suggests that optimizing the timing and location of ongoing efforts to reduce invasive vegetation cover may be key to avian conservation by increasing waterbird habitat. [ABSTRACT FROM AUTHOR]

We provide brief summaries of the individual presentations and then summarize the conversation on future research directions, the potential for nucleation to address restoration needs, and the challenges of integrating nucleation into restoration practices. She noted that disturbances which disrupt local positive feedback dynamics in the system may pose a specific challenge to the utility of nucleation, so disturbance type is a key consideration when characterizing nucleation dynamics. She noted that these intertidal grasslands exhibit nucleation dynamics, highlighting that system recovery hinges on clonal expansion of surviving cordgrass patches after disturbance events (Angelini et al. 2016). Her research employs the stricter definition of nucleation (Michaels et al. 2020) and as such, tests for local scale positive feedback and the patch size needed to generate an autocatalytic nucleation event. [Extracted from the article]

Ecosystems are degrading world‐wide, with severe ecological and economic consequences. Restoration is becoming an important tool to regain ecosystem services and preserve biodiversity. However, in harsh ecosystems dominated by habitat‐modifying organisms, restoration is often expensive and failure prone. Establishment of such habitat modifiers often hinges on self‐facilitation feedbacks generated by traits that emerge when individuals aggregate, causing density‐ or patch size‐dependent establishment thresholds. To overcome these thresholds, adult or juvenile habitat‐forming species are often transplanted in clumped designs, or stress‐mitigating structures are deployed. However, current restoration approaches focus on introducing or facilitating a single life stage, while many habitat modifiers experience multiple bottlenecks throughout their life as they transition through sequential life stages.Here, we define and experimentally test 'life cycle informed restoration', a restoration concept that focuses on overcoming multiple bottlenecks throughout the target species' lifetime. To provide proof of concept, and show its general applicability, we carried out complementary experiments in intertidal soft‐sediment systems in Florida and the Netherlands where oysters and mussels act as reef‐building habitat modifiers. We used biodegradable structures designed to facilitate bivalve reef recovery by both stimulating settlement with hard and fibrous substrates and post‐settlement survival by reducing predation.Our trans‐Atlantic experiments demonstrate that these structures enabled bivalve reef formation by: (a) facilitating larval recruitment via species‐specific settlement substrates, and (b) enhancing post‐settlement survival by lowering predation. In the Netherlands, structures with coir rope most strongly facilitated mussels by providing fibrous settlement substrate, and predation‐lowering spatially complex hard attachment substrate. In Florida, oysters were greatly facilitated by hard substrates, while coir rope proved unbeneficial.Synthesis and applications. Our findings demonstrate that artificial biodegradable reefs can enhance bivalve reef restoration across the Atlantic by mimicking emergent traits that ameliorate multiple bottlenecks over the reef‐forming organism' life cycle. This highlights the potential of our approach as a cost‐effective and practical tool for nature managers to restore systems dominated by habitat modifiers whose natural recovery is hampered by multiple life stage‐dependent bottlenecks. Therefore, investment in understanding how to achieve life cycle informed restoration on larger scales and whether the method it is applicable to restore other ecosystems is now required. [ABSTRACT FROM AUTHOR]

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Food webs are an integral part of every ecosystem on the planet, yet understanding the mechanisms shaping these complex networks remains a major challenge. Recently, several studies suggested that non-trophic species interactions such as habitat modification and mutualisms can be important determinants of food web structure. However, it remains unclear whether these findings generalize across ecosystems, and whether non-trophic interactions affect food webs randomly, or affect specific trophic levels or functional groups. Here, we combine analyses of 58 food webs from seven terrestrial, freshwater and coastal systems to test (1) the general hypothesis that non-trophic facilitation by habitat-forming foundation species enhances food web complexity, and (2) whether these enhancements have either random or targeted effects on particular trophic levels, functional groups, and linkages throughout the food web. Our empirical results demonstrate that foundation species consistently enhance food web complexity in all seven ecosystems. Further analyses reveal that 15 out of 19 food web properties can be well-approximated by assuming that foundation species randomly facilitate species throughout the trophic network. However, basal species are less strongly, and carnivores are more strongly facilitated in foundation species' food webs than predicted based on random facilitation, resulting in a higher mean trophic level and a longer average chain length. Overall, we conclude that foundation species strongly enhance food web complexity through non-trophic facilitation of species across the entire trophic network. We therefore suggest that the structure and stability of food webs often depends critically on non-trophic facilitation by foundation species. [ABSTRACT FROM AUTHOR]

Climate change and other anthropogenic stressors are converging on coastal ecosystems worldwide. Understanding how these stressors interact to affect ecosystem structure and function has immediate implications for coastal planning, however few studies quantify stressor interactions. We examined past and potential future interactions between two leading stressors on New England salt marshes: sea-level rise and marsh crab (Sesarma reticulatum) grazing driven low marsh die-off. Geospatial analyses reveal that crab-driven die-off has led to an order of magnitude more marsh loss than sea-level rise between 2005 and 2013. However, field transplant experimental results suggest that sea-level rise will facilitate crab expansion into higher elevation marsh platforms by inundating and gradually softening now-tough high marsh peat, exposing large areas to crab-driven die-off. Taking interactive effects of marsh softening and concomitant overgrazing into account, we estimate that even modest levels of sea-level rise will lead to levels of salt marsh habitat loss that are 3x greater than the additive effects of sea-level rise and crab-driven die-off would predict. These findings highlight the importance of multiple stressor studies in enhancing mechanistic understanding of ecosystem vulnerabilities to future stress scenarios and encourage managers to focus on ameliorating local stressors to break detrimental synergisms, reduce future ecosystem loss, and enhance ecosystem resilience to global change. [ABSTRACT FROM AUTHOR]

Explaining variability in the strength and sign of trophic interactions between primary consumers and plants is a long-standing research challenge. Consumer density and body size vary widely in space and time and are predicted to have interactive effects on consumer-plant interactions. In a southern US salt marsh, we used replicate field enclosures to orthogonally manipulate the body size (mass) and density of a dominant consumer (a snail). We investigated impacts (leaf damage and biomass) on monocultures of cordgrass, the foundation species, over three months. Increasing consumer density and body size increased leaf damage additively and, as predicted, multiplicatively reduced plant biomass. Notably, size and density determined the sign of consumer impact on plants: low to medium densities of small consumers enhanced, while high densities of large consumers strongly suppressed, plant biomass. Finally, total consumer metabolic biomass (mass0.75) within an enclosure parsimoniously explained plant biomass response, supporting theoretical predictions and suggesting that multiplicative effects of density and body size resulted from their effects on total metabolic biomass. The consequences of changes in consumer density and body size resulting from anthropogenic perturbations may therefore be predicted based on metabolic biomass. [ABSTRACT FROM AUTHOR]

Facilitation cascades are chains of positive interactions that occur as frequently as trophic cascades and are equally important drivers of ecosystem function, where they involve the overlap of primary and secondary, or dependent, habitat-forming foundation species [ 1 ]. Although it is well recognized that the size and configuration of secondary foundation species' patches are critical features modulating the ecological effects of facilitation cascades [ 2 ], the mechanisms governing their spatial distribution are often challenging to discern given that they operate across multiple spatial and temporal scales [ 1 , 3 ]. We therefore combined regional surveys of southeastern US salt marsh geomorphology and invertebrate communities with a predator exclusion experiment to elucidate the drivers, both geomorphic and biotic, controlling the establishment, persistence, and ecosystem functioning impacts of a regionally abundant facilitation cascade involving habitat-forming marsh cordgrass and aggregations of ribbed mussels. We discovered a hierarchy of physical and biological factors predictably controlling the strength and self-organization of this facilitation cascade across creekshed, landscape, and patch scales. These results significantly enhance our capacity to spatially predict coastal ecosystem function across scales based on easily identifiable metrics of geomorphology that are mechanistically linked to ecological processes. Replication of this approach across vegetated coastal ecosystems has the potential to support management efforts by elucidating the multi-scale linkages between geomorphology and ecology that, in turn, define spatially explicit patterns in community assembly and ecosystem functioning. • Tidal prism controls creekshed density of cordgrass-mussel facilitation cascade • Elevation and creek proximity drive mussel recruitment and growth across landscapes • Associational defenses control survivorship and aggregative behavior at patch scale • Geomorphology can be used to predict population patterns and ecosystem function Facilitation cascades widely enhance ecosystem function, but drivers of their spatially inconsistent patterning are unclear. Crotty and Angelini therefore elucidate the geomorphological, physical, and biological drivers that predictably control the presence and magnitude of the facilitation cascade between salt marsh cordgrass and ribbed mussels. [ABSTRACT FROM AUTHOR]

Decreasing frequency of freeze events due to climate change is enabling the poleward range expansion of mangroves. As these tropical trees expand poleward, they are replacing herbaceous saltmarsh vegetation. Mangroves and saltmarsh vegetation are ecosystem engineers that are typically viewed as having similar ecosystem functions. However, few studies have investigated whether predation regimes, community structure, and ecosystem functions are shifting at the saltmarsh-mangrove ecotone. In this study, we manipulated predator access to marsh and mangrove creekside habitats to test their role in mediating vegetation and invertebrate structure and stability in a two-year experiment. We also conducted a survey to evaluate how shifting vegetation is modifying structural complexity, invertebrate communities, and ecosystem functioning at the ecotone. Excluding larger (> 2 cm diameter) predators did not affect vegetation or invertebrate structure or stability in either saltmarsh or mangrove habitats. The survey revealed that the two habitat types consistently differ in structural metrics, including vegetation height, inter-stem distance, and density, yet they support similar invertebrate and algal communities, soil properties, and predation rates. We conclude that although mangrove range expansion immediately modifies habitat structural properties, it is not altering larger predator consumptive effects, community stability, community composition, or some other ecosystem functions and properties at the ecotone. [ABSTRACT FROM AUTHOR]

Ecosystem restoration can increase the health and resilience of nature and humanity. As a result, the international community is championing habitat restoration as a primary solution to address the dual climate and biodiversity crises. Yet most ecosystem restoration efforts to date have underperformed, failed, or been burdened by high costs that prevent upscaling. To become a primary, scalable conservation strategy, restoration efficiency and success must increase dramatically. Here, we outline how integrating ten foundational ecological theories that have not previously received much attention — from hierarchical facilitation to macroecology — into ecosystem restoration planning and management can markedly enhance restoration success. We propose a simple, systematic approach to determining which theories best align with restoration goals and are most likely to bolster their success. Armed with a century of advances in ecological theory, restoration practitioners will be better positioned to more cost-efficiently and effectively rebuild the world's ecosystems and support the resilience of our natural resources. Silliman and colleagues outline how restoration practitioners can leverage insight from ecological theories to increase the scale, success, and resilience of habitat restorations. [ABSTRACT FROM AUTHOR]

Although there is mounting evidence that biodiversity is an important and widespread driver of ecosystem multifunctionality, much of this research has focused on small-scale biodiversity manipulations. Hence, which mechanisms maintain patches of enhanced biodiversity in natural systems and if these patches elevate ecosystem multifunctionality at both local and landscape scales remain outstanding questions. In a 17 month experiment conducted within southeastern United States salt marshes, we found that patches of enhanced biodiversity and multifunctionality arise only where habitat-forming foundation species overlap—i.e. where aggregations of ribbed mussels (Geukensia demissa) form around cordgrass (Spartina alterniflora) stems. By empirically scaling up our experimental results to the marsh platform at 12 sites, we further show that mussels—despite covering only approximately 1% of the marsh surface—strongly enhance five distinct ecosystem functions, including decomposition, primary production and water infiltration rate, at the landscape scale. Thus, mussels create conditions that support the co-occurrence of high densities of functionally distinct organisms within cordgrass and, in doing so, elevate salt marsh multifunctionality from the patch to landscape scale. Collectively, these findings suggest that patterns in foundation species' overlap drive variation in biodiversity and ecosystem functioning within and across natural ecosystems. We therefore argue that foundation species should be integrated in our conceptual understanding of forces that moderate biodiversity–ecosystem functioning relationships, approaches for conserving species diversity and strategies to improve the multifunctionality of degraded ecosystems. [ABSTRACT FROM AUTHOR]