Managed relocation, the purposeful movement of species (assisted migration) or genotypes (assisted gene flow) beyond their historical range, might support population persistence under climate change but entails a variety of risks. Assisted migration risks accidentally invasive species negatively impacting recipient communities, and assisted gene flow risks loss of local adaptation to non-climatic factors and loss of metapopulation-level genetic diversity. This question of the balance of risks and benefits of managed relocation directly parallels the broader ecological question of the potential for connectivity to lead to a trade-off between diversity maintenance and mobilization. Too little connectivity might limit local response to disturbance and change as it depends on genetic or demographic rescue; too much connectivity might have the homogenizing influence of eroding total diversity and therefore overall adaptive or response capacity to environmental change. An understanding of this trade-off is inherent to the theories of gene flow and local adaptation and of the interactive roles of environmental variation, dispersal, and species interactions in driving community assembly. In this talk, I will synthesize the theory of diversity maintenance-mobilization trade-offs across population and community levels to inform expectations for the drivers and balance of the risks and benefits of managed relocation.
In the theory of gene flow and local adaptation, dispersal and any resulting gene flow can enhance local genetic diversity (increased diversity mobilization), but any resulting reduction in local adaptation given spatial environmental heterogeneity in selection can decrease total population diversity (decreased diversity maintenance). Example factors that decrease the strength of this trade-off include increasing selection strength, frequency-dependent selection based on resource monopolization, stochasticity in dispersal, the existence of locally small or declining populations susceptible to drift, and temporal variability in selection. In the theory of community assembly, dispersal typically increases alpha diversity (increased diversity mobilization) but decreases beta and gamma diversity (decreased diversity maintenance). Example factors that decrease the strength of this trade-off include increasing primary productivity, decreasing disturbance, and an increasing total species pool. These factors that influence diversity maintenance-mobilization trade-offs across population and community levels suggest (i) information likely to be necessary for effective management decision-making (e.g., the degree of environmental stochasticity), (ii) potential indicators of the level of risk in managed relocation (e.g., primary productivity), and (iii) approaches that might reduce the risks of managed relocation (e.g., mimicking stochastic dispersal).