Trophic rewilding benefits a tropical community through direct and indirect network effects

Abstract

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.

Supporting the restoration of complex ecosystems requires long‐term and multi‐scale perspectives

“…Together, the studies of this Special Issue highlight how restoration initiatives in the Anthropocene should focus on conserving and promoting ecological complexity and emergent properties at multiple scales and nurturing the processes responsible for the long‐term maintenance of high biodiversity levels and ecological resilience (Bullock et al 2021, Mittelman et al 2021, Storch et al 2021). They emphasize the need for integrating pluralistic values of nature in restoration research and planning in order to find the required support to implement restoration at scale (Quintero‐Uribe et al 2022).…”

“…The prediction that higher ecological complexity is linked to enhanced emergent properties such as ecosystem function and resilience finds support in two studies using theoretical approaches (Storch et al 2021) and trophic network modelling (Mittelman et al 2021). Storch et al (2021) use the theoretical framework of the equilibrium theory of biodiversity dynamics (ETBD) to demonstrate that relatively high equilibrium biodiversity levels can be achieved by nurturing the resource fluxes necessary for the maintenance of stable total community abundance and biomass production.…”

“…Community biomass and diversity can also be enhanced by ensuring the presence of trophic interactions that control dominant competitors as well as the presence of ecosystem engineers. In a modelling study on ecological networks in an Atlantic Forest site in Brazil, Mittelman et al (2021) demonstrate the importance of restoring trophic network complexity. They show that restoring three frugivore keystone species has disproportionate impacts on the structure and properties of trophic networks, with an increase in network connectance, nestedness, robustness and number of pathways that is greater than the sum of isolated effects for each species.…”

“…Papers in this special issue cover from local‐scale studies (Mittelman et al 2021, Zhang et al 2021) to continental (Segar et al 2021, Quintero‐Uribe et al 2022) and global (Monsarrat and Svenning 2021, Storch et al 2021, Vynne et al 2022), highlighting a growing interest for restoration research from a broad range of spatial perspectives.…”

Using ecological networks to answer questions in global biogeography and ecology

“…historical records of ecological interactions), it may be possible to predict effects in unsampled regions using phylogenetically structured networks (Raimundo et al, 2018), trait‐matching (Pichler et al, 2020) and/or other methods that operate independently of species identities (which change across biogeographical space). As an example, in plant–frugivore networks large bodied organisms are able to disperse larger seeds, thus reintroducing large organisms to regions where they are extinct may contribute to the regeneration of plant communities (Mittelman et al, 2022).…”