Species reintroduction and community-level consequences in dynamically simulated ecosystems

Global biodiversity, and its associated ecosystem services, are threatened due to species extinctions. Reintroducing locally extinct species may be a partial solution to this problem. However, the success and possible consequences of any artificial reintroduction will depend on its ecological community, and the reaction of that community to the species' extinction and reintroduction. Mathematical models can offer useful insights by identifying the key features of communities and reintroduced species most likely to result in successful reintroductions. Here we simulated extinctions and reintroductions for a range of theoretical food webs generated using an established bioenergetics model. This allows the probability of successful reintroductions to be quantified as a function of two important ecological factors: the connectance of the food web, and of the time between extinctions and reintroductions. Reintroduction success is measured across an ensemble of 1796 simulated communities, with connnectances of 0.05, 0.15 and 0.3, using three criteria: presence of the reintroduced species in the final community, unchanged species richness in the final community compared to the pre-extinction persistent community and the complete restoration of the community (including both species richness and equilibrium biomass distributions). Although only 12 reintroduced species fail to re-establish according to minimal criteria, the process of extinction and reintroduction frequently has a large effect on the community composition. Increasing time to reintroduction increases both the probability of species loss, and equilibrium biomass change in the community. Proportionally, these community-level impacts occur more frequently when the reintroduced species is a primary producer or top predator. These results indicate that ignoring broader measures of reintroduction success could seriously underestimate the impact of reintroductions on the ecological community. These quantitative results can be compared to empirical literature and may help reveal which factors are most important to the success of reintroductions.