Movement and mixing in a managed metapopulation
Animal movement connects otherwise isolated social groups and populations across the landscape, influencing demographic persistence and promoting gene flow. For endangered species with small, fragmented populations, managers often rely on metapopulation theory to guide conservation efforts and regulate movement between populations. Here, we evaluate the consequences of managed movement on the genetic and demographic viability of the red wolf (Canis rufus) and test the application of metapopulation theory to guide management of a highly endangered predator.
Red wolves historically occurred throughout the southeastern United States, but were decimated by habitat alteration and predator control programs, and were declared extinct-in-the-wild by 1980. The establishment of an ex situ population allowed persistence of red wolves and facilitated a reintroduction program that continues today. The species currently exists as a metapopulation with ex and in situ populations connected via managed releases to the wild. We analyzed over 40 years of individual-level data on red wolves to quantify the genetic and demographic impacts of historic movement between populations. We also constructed an agent-based metapopulation model to predict the impacts of continued movement on the species’ long-term persistence and genetic diversity, and to evaluate the capacity of the species to meet recovery objectives.
Since 1987, managers have released over 130 wolves to restoration areas in North Carolina, although release rates have varied from 1-15/year. Released wolves have fared well demographically: they have similar first-year survivorship to wild-born wolves (49.3% vs. 51.9%), but intriguingly have a significantly higher probability of reproducing than wild-born wolves (25.3% vs. 8.0%). Releases have allowed the reintroduced population to establish and grow, and in 2000, with the wild population approaching 100 animals, managers decreased releases from 5.9 to 3.9/year.
Contrary to theoretical expectations, releases have not caused the populations to synchronize dynamics, likely due to differences in vital rates between populations (survivorship and reproduction are significantly higher ex situ). Continued movement is having important genetic impacts on the reintroduced population, however, as there is a significantly positive relationship between the annual release rate and the amount of gene diversity retained in the population. Our model indicates that continued movement between populations will promote retention of gene diversity and demographic stability across the metapopulation, allowing the red wolf to meet long-term recovery objectives. To achieve necessary movement rates, however, ex situ breeding must increase by >14%. This study highlights the application of metapopulation theory to manage species of conservation concern.