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Defaunation has a major driver of biodiversity loss in tropical forests. Here we discuss how to reverse defaunation by re-introducing key species in defaunated or restored forests.

Rewilding has been an increasingly popular tool to restore plant–animal interactions and ecological processes impaired by defaunation. However, the reestablishment of such processes has seldom been assessed. We investigated the restoration of ecological interactions following the reintroduction of the brown howler monkey (Alouatta guariba) to a defaunated Atlantic forest site. We expected the reintroduction to restore plant–animal interactions and interactions between howlers and dung beetles, which promote secondary seed dispersal. We estimated the number of interactions expected to be restored by the reintroduction to provide the baseline interaction richness that could be restored. We followed the reintroduced howler monkeys twice a week for 24 months (337 hours total) to assess their diet. We used howler monkey dung in secondary seed dispersal experiments with 2484 seed mimics to estimate the removal rates by dung beetles and collected the beetles to assess community attributes. We compared the potential future contribution of howler monkeys and other frugivores to seed dispersal based on the seed sizes they disperse in other areas where they occur. In 2 years, howler monkeys consumed 60 animal-dispersed plant species out of the 330 estimated. Twenty-one dung beetle species were attracted to experimentally provided dung; most of them were tunnelers, nocturnal, and large-sized (>10 mm). On average 30% (range 0–100%) of the large seed mimics (14 mm) were moved by dung beetles. About 91% of the species consumed by howlers (size range 0.3–34.3 mm) overlapped in seed size with those removed by dung beetles. In our study area, howler monkeys may consume more large-seeded fruit species than most other frugivores, highlighting their potential to affect forest regeneration. Our results show reintroductions may effectively restore ecological links and enhance ecological processes. El resalvajamiento cada vez crece más como una herramienta popular para restaurar las interacciones entre animales y plantas, así como los procesos ecológicos perjudicados por la pérdida de fauna. Sin embargo, el restablecimiento de dichos procesos ha sido poco evaluado. Investigamos la restauración de las interacciones ecológicas después de la reintroducción del mono aulladorpardo (Alouatta guariba) a un sitiode bosque atlántico con pérdida de fauna. Nuestras expectativas planteaban que la reintroducción restauraría las interacciones planta–animal y las interacciones entre los monos y los escarabajos peloteros, la cual promueve la dispersión secundaria de semillas. Estimamos que el número de interacciones que se esperaba fueran restauradas proporcionaría la línea base para la riqueza de interacciones que podría ser restaurada. Seguimos a los monos aulladores reintroducidos dos veces por semana durante 24 meses (227 horas en total) para evaluar su dieta. Usamos las excretas de los monos en experimentos de dispersión secundariade semillas con 2484 imitaciones de semilla para estimar las tasas de extracción por parte de los escarabajos peloteros y luego los colectamos para evaluar los atributos de la comunidad. Comparamos la potencial contribución futura de los monos aulladores y otros frugívoros para la dispersión de semillas con base en el tamaño de las semillas que dispersan en otras áreas en donde están presentes. En dos años los monos aulladores consumieron 60 especies de plantas dispersadas por animales de las 330 estimadas. Veintiún especies de escarabajos peloteros fueron atraídos por las excretas proporcionadas experimentalmente; la mayoría de ellas eran excavadoras de túneles, nocturnas, y grandes (>10 mm). En promedio, el 30% (rango 0 – 100%) de las imitaciones de semillas grandes (14 mm) fueron movidas por los escarabajos peloteros. Aproximadamente el 91% de las especies consumidas por los monos aulladores (rango del tamaño 0.3 – 34.3 mm) se traslaparon en cuanto a tamaño de la semilla con aquellas removidas por los escarabajos peloteros. Con base en nuestras estimaciones para el área de estudio, los monos aulladores consumieron más frutos con semillas grandes que la mayoría de los frugívoros, lo que resalta su potencial para afectar la regeneración del bosque. Nuestros resultados muestran que las reintroducciones pueden restaurar efectivamente las conexiones ecológicas y mejorar los procesos ecológicos.

Seed dispersal and predation are paramount for tropical plant diversity. When encountered by scatter-hoarding frugivores, seeds can be either eaten, dispersed or ignored. But even after dispersal, seed caches are still subjected to predation. Many factors are known to influence these dynamics; however, how frequently hoarders use certain patches has seldom been related to cache predation rates. We used the interaction between agoutis (Dasyprocta leporina), a scatter-hoarding rodent, and Joannesia princeps, a tropical tree, as a model to investigate how the number of visits by hoarders in certain areas influences cache predation and seed fate. Camera-traps were used for 30 days in twenty different locations in Tijuca National Park to assess number of visits by agoutis. Thereafter, we placed seed piles on the same areas and determined their fate using the spool-and-line method to track seeds for over one hundred days. We found a non-linear relationship between how often an area is used by hoarders and the final proportion of dispersed seeds. At areas with a low number of visits, proportion of dispersed seeds was low due to low removal. As frequency of visits by hoarders increased, seed removal and the number of dispersal events increased but so did cache predation. Thus, in areas intensively used by hoarders, high cache predation resulted in a low number of dispersed seeds that remained alive in caches. As a result, dispersal was maximized in areas with intermediate use by scatter-hoarders, where there was a balance between primary seed dispersal and cache predation.

Species reintroductions can be used as a conservation strategy to restore ecological interactions and the functionality of impoverished ecosystems. The ecological effects of reintroductions go beyond restoring pairwise interactions, because reintroductions can change how extant species are indirectly linked to each other in an ecological community. These indirect pathways, in turn, may shape a myriad of ecological and evolutionary processes operating in ecological systems. Here, we investigated how reintroductions may affect the direct and indirect pathways connecting species in ecological networks. We modeled the potential effects of the reintroduction of four frugivore species (channel‐billed toucans, red‐humped agoutis, brown howler monkeys and yellow‐footed tortoises) to the local seed dispersal network in an Atlantic Forest site, the Tijuca National Park (Rio de Janeiro, Brazil). We used a seed dispersal interaction dataset together with data on species occurrences in Tijuca to build network models. Then, we calculated how network structure and the total amount of indirect effects varied across simulated networks with and without the reintroduced species. Using random reintroduction simulations, we tested if the observed network changes were expected merely from the increase in species richness. The reintroduction of the frugivore species increased network connectance, nestedness, robustness, number of pathways and total amount of indirect effects in all simulated networks. The increase in number of pathways with the addition of the four reintroduced species was greater than the sum of isolated effects for each species, because some interaction pathways contained several reintroduced species. These changes in network metrics were significantly greater than if a randomly chosen set of four species was reintroduced. Furthermore, our results indicate that multiple reintroductions in the same area, known as refaunation, may have an even greater restoration effect than single species reintroductions through increased indirect connections in the network.

Rewilding has been intensely debated among conservationists and ecologists. Multiple definitions and conceptual frameworks have been proposed for rewilding programmes, but hitherto all with a focus on promoting biodiversity conservation via restoration of ecological processes. Recently, however, it has been proposed to instead focus rewilding on the promotion of self-sustaining provisioning of preferred ecosystem services. Such shift in focus comes with an increased risk that rewilding efforts could be designed towards the promotion of simplified ecosystems providing selected ecosystem services, despite negative effects on biodiversity, as well as considerable socio-economic risks and ethical problems. We argue that rewilding should keep its focus on promoting biodiversity, with provisioning of other ecosystem services being integrated in the design of rewilding projects only as co-benefits. If such services become the main motivation for rewilding projects, there is a risk of misinterpretations and rewilding promoting less diverse ecosystems.

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’.

Reintroduction has been recognized as a powerful conservation tool, but in order to ensure its success, animal monitoring is highly recommended. One way to monitor released animals is to put radiotelemetry collars on them. These devices, however, can harm the subjects, causing serious wounds. Our objectives in this work were to describe the injuries caused by a radiotelemetry collar model on reintroduced agoutis and to propose modifications to it. We equipped agoutis with TXE-311C radio collars (Telenax Wildlife Telemetry) before releasing them in the wild. They acquired serious wounds and one animal died. We then modified the collar structure to reduce its width and retention of water. After these modifications, the injuries did not occur again. As reintroduction is an expensive conservation strategy, any improvement that maximize its probability of success is important. We believe that the improvements we propose here have the potential to enhance the success of reintroductions and to increase animal welfare. This recommendation is more important when captive animals are re-introduced, because they tend to have lower immunity, particularly when they are released in rainy habitats. [PUBLICATION ABSTRACT]

As defaunation spreads through the world, there is an urgent need for restoring ecological interactions, thus assuring ecosystem processes. Here, we define the new concept of credit of ecological interactions, as the number of interactions that can be restored in a focal area by species colonization or reintroduction. We also define rewiring time, as the time span until all the links that build the credit of ecological interactions of a focal area have become functional again. We expect that the credit will be gradually cashed following refaunation in rates that are proportional to (1) the abundance of the reintroduced species (that is expected to increase in time since release), (2) the abundance of the local species that interact with them, and (3) the traits of reintroduced species. We illustrated this approach using a theoretical model and an empirical case study where the credit of ecological interactions was estimated. This new conceptual framework is useful for setting reintroduction priorities and for evaluating the success of conservation initiatives that aim to restore ecosystem services. Restoring ecosystem functioning is urgent. Herein, we develop a coherent, insightful new conceptual framework to study the recovering, rather than losing, of ecological interactions. We argue that defaunated areas should have a credit of ecological interactions that could be cashed through refaunation.

Large‐seeded plants are especially vulnerable to the loss of seed dispersers in small forest fragments. The palm Attalea humilis goes against this trend by reaching high abundances in small remnants. Productivity, seed dispersal and seed predation of A. humilis were investigated in two large (2400 and 3500 ha) and three small (19, 26 and 57 ha) Atlantic Forest fragments in southeastern Brazil. Palms in the small fragments produced more female inflorescences, resulting in a higher fruit production in these places. Seed dispersal rates were higher in the large fragments, where scatter hoarding was more frequent. Scolytine beetles were the main seed predators and damaged a larger number of seeds in small fragments, but predation by rodents and bruchine beetles was low irrespective of fragment size. As scolytines do not necessarily kill the seeds, low predation by bruchines and rodents, together with its own high productivity, allow A. humilis to be more abundant in small fragments despite the scarcity of its main dispersers. This increased abundance, by its turn, can increase competitive interactions between A. humilis and other plants in small fragments. Thus, abundance patterns of A. humilis are a good example of fragmentation affecting the balance of ecological interactions in a complex way, emphasizing the role of preserving ecological processes for conserving biodiversity in fragmented tropical landscapes. Abstract in Portuguese is available at http://www.blackwell‐synergy.com/loi/btp.

Because most invertebrate seed predators are host-specific, they are usually expected to produce Janzen-Connell patterns. This expectation was fulfilled for Astrocaryum but not for Allagoptera, depending on the effects of bruchine and scolytine predators on the seeds of these palms. Thus, the mere existence of invertebrate predation is not sufficient for generating Janzen-Connell; what matters is seed mortality, which varies between predators and between plant species for the same predator. Abstract in Portuguese is available at http://www.blackwell-synergy.com/loi/btp.