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

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 (Tijuca, 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, as
some interaction pathways contained several reintroduced species. These
changes in network metrics were significantly greater than if a randomly
chosen set of four species were 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.