The Portfolio Effect: Spreading the Risk in an Era of Environmental Uncertainty

Management strategies that increase biological diversity and promote varied approaches to population protection are more likely to succeed during a future where global warming drives rapid environmental change and increases uncertainty.  We describe how the concept of a diverse management portfolio can be applied to native trout conservation by increasing Representation (protecting/restoring diversity), Resilience (having sufficiently large populations and intact habitats to facilitate recovery from rapid environmental change), and Redundancy (saving enough different populations so that some can be lost without jeopardizing the species).  Saving diversity for native trout requires the conservation of genetically pure populations, the protection and restoration of life history diversity, and the protection of populations across the historical range.  Protecting stronghold populations is important because such populations will have a better chance of surviving future environmental disturbances.  The long-term persistence of populations is likely to require maintenance of larger population sizes and habitat patches than currently exist for many native trout populations.  Redundancy among these elements is important given that many populations are small, occupy reduced habitat in fragmented stream systems, and therefore are vulnerable to extirpation.  Application of the concept is further described in a case study of Bonneville cutthroat trout (Oncorhynchus clarkii utah).