3: Inferring demographic change during invasion and its quantifying its impact on invasion success
In the simplest model of a successful invasion, some small fraction of a native population is transported to a new environment where a viable population forms and increases in size over time. This leads to a demographic bottleneck (a decrease in population size followed by an increase), which can have wide-ranging implications for both practical and theoretical aspects of invasion genetics (see Box 2). From a pragmatic perspective, the extreme demographic dynamics of colonization can be used to reconstruct invasion events in time. From a biological perspective, invasion geneticists are tasked with explaining how so many invasive species form viable populations, let alone dominate foreign ecosystems, in the face of a population bottleneck that reduces genetic diversity and increases the risk of inbreeding depression (Estoup et al., 2016). We discuss these two perspectives separately.