Adding ecological and evolutionary processes to restoration biodiversity offset models using neutral theory

Aim: Biodiversity offsets are being implemented or planned across all continents and biogeographical realms. Due to their popularity, new offset projects have developed faster than empirical evidence of their ecological effectiveness, so policy has been informed by quantitative models. However, these models have yet to incorporate ecological and evolutionary processes, which vary globally. Here we use the unified neutral theory of biodiversity to integrate speciation and dispersal into models of restoration biodiversity offsets.

Location: A simulated one-dimensional circular landscape.

Methods: We designed a simulation framework based on neutral theory that allowed us to compare restoration biodiversity offsets under various scenarios of speciation, dispersal and offset implementation: no offsets, passive restoration and translocation. This approach allowed us to evaluate time-series of multiple metrics of biodiversity (richness, evenness and community similarity) at different spatial scales (patch and landscape), which were then compared using model-based recursive partitioning.

Results: The choice of offset implementation was the main determinant of successful offset outcomes; translocation consistently had the best outcomes. Passive restoration only improved offset outcomes for systems with high speciation rates. Speciation and dispersal mainly played a secondary role in offset outcomes, with dispersal only affecting offset outcomes at landscape scales. Outcomes also varied across different metrics of biodiversity, with species richness and evenness showing opposing trajectories for some scenarios.

Main conclusions: Although ecological and evolutionary processes affect biodiversity offset outcomes, the type of offset implementation remains the most important determinant of offset success. This emphasises the development – and effective implementation – of robust offset policies and guidelines that include active translocation and demand more than just passive restoration.