source_sink_vital_rates_Jun2024

We use 26 years of data on reproduction, movement, and survival to estimate annual source-sink dynamics of the Everglade snail kite (Rostrhamus sociabilis plumbeus), an endangered wetland-dependent raptor in the United States. The biological invasion of a non-native apple snail (Pomacea maculata) provides a supplementary food source for snail kites and the increased prey availability has been linked to increases in reproduction, survival, body mass, and population growth. This analysis estimates fecundity, survival, and movement parameters as a function of years since invasion and how source-sink dynamics changed over time.
The Everglade snail kite forms a spatially structured population limited to flooded freshwater wetlands and shallow lakes in peninsular Florida in the United States. Our study area includes all known breeding areas for the Everglade snail kite. Wetlands were grouped into 6 populations based on geographic location and hydrology: Paynes Prairie, Kissimmee River Valley, Okeechobee, Everglades, East, and St. John’s Marsh.
For each vital rate (demographic parameter) we included linear, quadratic, and logarithmic effects of years since P. maculata invasion. We tested for interactive effects between years since invasion and snail kite age because the invasion may have affected younger birds differently. Here, the top models for each demographic rate are presented, please see (Beatty et al. for the full model list).
To compare pre- and post-invasion estimates, a pre-invasion value was estimated for each vital rate using data before each population was invaded. Pre-invasion values were estimated separately to be able to estimate the distinct relationship between vital rates and time since invasion and because we expected patterns in vital rates to be different before the invasion. Pre-invasion estimates are a single value for each population and therefore do not vary with years since invasion. The Paynes Prairie population did not have snail kites breeding in it until after it was invaded and therefore pre-invasion data is missing for this site and years since invasion represents the number of years since snail kites began breeding in the invaded site.