Rewilding South America: Ten key questions

Resource partitioning in a novel herbivore assemblage in South America

Human-induced species declines and extinctions have led to the downsizing of large-herbivore assemblages, with implications for many ecosystem processes. Active reintroduction of extirpated large herbivores or their functional equivalents may help to reverse this trend and restore diverse ecosystems and their processes. However, it is unclear whether resource competition between native and non-native herbivores could threaten restoration initiatives, or to what extent (re)introduced species may influence local vegetation dynamics. To answer these questions, we investigated the diets of a novel South American herbivore assemblage that includes resident native species, reintroduced native species and introduced non-native species. We examined plant composition, diet breadth and the overlap between species to describe the local herbivory profile and the potential for resource competition. Using DNA metabarcoding on faecal samples (n = 465), we analysed the diets of the herbivore assemblage in the Rincón del Socorro rewilding area of Iberá National Park, Argentina. We compared the species richness of faecal samples, the occurrence of plant families/growth forms and the compositional similarity of samples (inter- and intraspecifically). Our results indicate species-level taxonomic partitioning of plant resources by herbivores in this system. Differences in sample richness, composition and diet breadth reflected a diverse range of herbivory strategies, from grazers (capybara) to mixed feeders/browsers (brocket deer, lowland tapir). Differences in diet compositional similarity (Jaccard) revealed strong taxonomic resource partitioning. The two herbivores with the most similar diets (Pampas deer and brocket deer) still differed by more than 80%. Furthermore, all but one species (axis deer) had more similar diet composition intraspecifically than compared to the others. Overall, we found little evidence for resource competition between herbivore species. Instead, recently reintroduced native species and historically introduced non-natives are likely expanding the range of herbivory dynamics in the ecosystem. Further research will be needed to determine the full ecological impacts of these (re)introduced herbivores. In conclusion, we show clear differences in diet breadth and composition among native, reintroduced and non-native herbivore species that may be key to promoting resource partitioning, species coexistence and the restoration of ecological function.

Agricultural wilding: rewilding for agricultural landscapes through an increase in wild productive systems

Introducing wild crops and plants complements intentions for improved biodiversity outcomes in agricultural landscapes; and provides opportunity for in-situ conservation of a diverse range of wild plants and crops, and improved connectivity between conserved areas. This opinion article considers definitions and common value of conserving wild crops and plants, and crop wild relatives, in-situ and ex-situ. Rewilding definitions and common uses for policy and practice are described. The Ecological Sensitivity within Human Realities (ESHR) concept was developed to guide human natural-environment interactions in agricultural systems and landscapes for improved functional biodiversity outcomes. It is used to assess possible appropriateness of rewilding for agricultural systems and landscapes. The assessment demonstrates how agricultural systems and landscapes are often excluded, despite appearing a useful term to encourage such conservation efforts. The importance of a more specific term rather than a more specific definition and use of rewilding is suggested. Agricultural wilding is introduced as a more specific term for introducing and conserving wild crops and plants for agricultural purposes, as wild productive systems, useful for policy or other approaches the guide human natural-environment interactions. The conceptual approach to the article provides theoretical suggestions for minimum proportions of wild crops and plants for wild productive systems according to native and non native landscapes. From a conceptual to applied discussion, relevance of agricultural wilding for coffee farming landscapes is explained in some depth, and for an existing biodiversity campaign and an EU agricultural policy, briefly.

Ecology of a widespread large omnivore, Homo sapiens, and its impacts on ecosystem processes

Discussions of defaunation and taxon substitution have concentrated on megafaunal herbivores and carnivores, but mainly overlooked the particular ecological importance of megafaunal omnivores. In particular, the Homo spp. have been almost completely ignored in this context, despite the extinction of all but one hominin species present since the Plio-Pleistocene. Large omnivores have a particular set of ecological functions reflecting their foraging flexibility and the varied disturbances they create, functions that may maintain ecosystem stability and resilience. Here, we put the ecology of Homo sapiens in the context of comparative interspecific ecological roles and impacts, focusing on the large omnivore guild, as well as comparative intraspecific variation, focusing on hunter-gatherers.We provide an overview of the functional traits of H. sapiens, which can be used to spontaneously provide the functions for currently ecologically extinct or endangered ecosystem processes. We consider the negative impacts of variations in H. sapiens phenotypic strategies, its possible status as an invasive species, and the potential to take advantage of its learning capacities to decouple negative and positive impacts.We provide examples of how practices related to foraging, transhumance, and hunting could contribute to rewilding-inspired programs either drawing on hunter-gatherer baselines of H. sapiens, or as proxies for extinct or threatened large omnivores. We propose that a greater focus on intraspecific ecological variation and interspecific comparative ecology of H. sapiens can provide new avenues for conservation and ecological research.

Estimating interaction credit for trophic rewilding in tropical forests

Trophic rewilding has been suggested as a restoration tool to restore ecological interactions and reverse defaunation and its cascading effects on ecosystem functioning. One of the ecological processes that has been jeopardized by defaunation is animal-mediated seed dispersal. Here, we propose an approach that combines joint species distribution models with occurrence data and species interaction records to quantify the potential to restore seed-dispersal interactions through rewilding and apply it to the Atlantic Forest, a global biodiversity hotspot. Using this approach, we identify areas that should benefit the most from trophic rewilding and candidate species that could contribute to cash the credit of seed-dispersal interactions in a given site. We found that sites within large fragments bearing a great diversity of trees may have about 20 times as many interactions to be cashed through rewilding as small fragments in regions where deforestation has been pervasive. We also ranked mammal and bird species according to their potential to restore seed-dispersal interactions if reintroduced while considering the biome as a whole and at finer scales. The suggested approach can aid future conservation efforts in rewilding projects in defaunated tropical rainforests.This article is part of the theme issue 'Trophic rewilding: consequences for ecosystems under global change'.

Measuring rewilding progress

Rewilding is emerging as a promising restoration strategy to enhance the conservation status of biodiversity and promote self-regulating ecosystems while re-engaging people with nature. Overcoming the challenges in monitoring and reporting rewilding projects would improve its practical implementation and maximize its conservation and restoration outcomes. Here, we present a novel approach for measuring and monitoring progress in rewilding that focuses on the ecological attributes of rewilding. We devised a bi-dimensional framework for assessing the recovery of processes and their natural dynamics through (i) decreasing human forcing on ecological processes and (ii) increasing ecological integrity of ecosystems. The rewilding assessment framework incorporates the reduction of material inputs and outputs associated with human management, as well as the restoration of natural stochasticity and disturbance regimes, landscape connectivity and trophic complexity. Furthermore, we provide a list of potential activities for increasing the ecological integrity after reviewing the evidence for the effectiveness of common restoration actions. For illustration purposes, we apply the framework to three flagship restoration projects in the Netherlands, Switzerland and Argentina. This approach has the potential to broaden the scope of rewilding projects, facilitate sound decision-making and connect the science and practice of rewilding.This article is part of the theme issue 'Trophic rewilding: consequences for ecosystems under global change'.

Governing with nature: a European perspective on putting rewilding principles into practice

Academic interest in rewilding is moving from commentary to discussion on future research agendas. The quality of rewilding research design will be enhanced if it is informed by knowledge of the rewilding practice. Here, we describe the conceptual origins and six case study examples of a mode of rewilding that emerged in the Dutch Delta and is being promoted and supported by Rewilding Europe, an umbrella organization established in 2011. The case experiences presented help position this version of rewilding in relation to the US 3C's version and point towards a rewilding action philosophy characterized by pragmatic realism and pioneer projects around which multiactor networks interested in policy innovation and change form. We argue that scaling-up the models of rewilding presented is constrained by institutional cultures and will require innovations in conservation finance and business models. Nonetheless, we suggest that the expanding European Rewilding Network and associated facilities, such as the European Wildlife Bank, represent a valuable asset for natural science research, aimed at exploring the ecological impacts of grazing and the relationship between role of restored herbivore guilds and biotical expansion, and for social science research investigating concepts such as non-human agency and autonomy. Lastly, we ask applied scientists to view rewilding as an uncertain and unfolding conservation approach and to refrain from seeking to specify it as a management approach supporting the delivery of pre-determined targets and/or ideals. This is because such actions may constrain the transformative potential of rewilding practice.This article is part of the theme issue 'Trophic rewilding: consequences for ecosystems under global change'.