Recent Advances and Current Challenges in Applying Source-Sink Theory to Species Conservation

Purpose of Review The source-sink paradigm has been a powerful tool for focusing theoretical and empirical explorations of population dynamics in heterogeneous landscapes. The prevalence of suspected source-sink dynamics in empirical studies would lead to the conclusion that sources and sinks are common. However, important questions remain about how source-sink dynamics have been assessed in past studies and the degree to which current approaches apply to atypical populations and dynamic landscapes. Recent Findings We reviewed 432 papers that directly addressed source-sink dynamics between 1985 and 2018. We found that the majority of studies focused on birds, mammals, and forested systems. In recent years, however, the number of aquatic invertebrate and marine studies increased, as did the tendency to focus on conservation or management goals and to report population trends. Although 79% of papers claimed to identify source-sink dynamics, only 13% of studies based their assessment on all four measures of reproduction, mortality, immigration, and emigration. Nearly 23% of all studies used neither demographic nor movement metrics to make conclusions about the presence of source-sink dynamics. Summary Source-sink theory and practice has matured and is increasingly relevant for species conservation and management. However, we lack a clear understanding of the conditions under which limited data can defensibly support source-sink assessments and be scaled up to the extent at which resource decisions are made. In the absence of this, future studies will need to take a more rigorous approach to defining sources and sinks to better gauge the prevalence of source-sink dynamics.