Abstract
Source-sink dynamics are a cornerstone of theory for spatially structured populations. Despite long-standing interest, understanding temporal variation in source-sink dynamics in wild populations remains rare. Biological invasions have the potential to alter source-sink dynamics for native species, which may change over time as invasions proceed. We used 28 years of data on reproduction, movement, and survival to estimate annual source-sink dynamics across the entire range of the endangered Everglade snail kite (Rostrhamus sociabilis plumbeus) during the invasion of a novel prey species, the island apple snail (Pomacea maculata). Snail kite populations underwent striking changes in source-sink dynamics with time since invasion, and no population was consistently a source or sink over time. Some initial benefits of increased prey availability on snail kite demography were diminished in the long term. Populations invaded by P. maculata impacted uninvaded populations via changes in snail kite retention (i.e., lack of movement) and emigration across the metapopulation. Our findings illustrate how effects of biological invasions can change over time and may take decades to fully emerge, and they emphasize how an invasive species can have distant impacts on uninvaded populations via fluctuations in native species' local retention and emigration. In addition, our results demonstrate how fluctuating emigration and retention alter long-term interpretations of source-sink dynamics through variation in local versus landscape contributions of populations to the metapopulation, highlighting that the status of "source" or "sink" can be highly variable through time.