Modelling the Impact of Dispersal on a Natal Population that Exhibits Boom-Bust Dynamics

Dispersal, an important form of movement, influences population dynamics, species distribution, and gene flow between populations. In population models, dispersal is often included in a simplified manner by removing a random proportion of the population. Many ecologists now argue that models should be formulated at the individual-level instead of the population-level to accurately capture how dispersal affects population dynamics. This is especially true for populations exhibiting boom-bust dynamics as these often harbour specialised disperser morphs, life histories or behaviours, as dispersal is essential for persistence. Within a management context, such dynamics play a key role in the stability of populations and in turn extinction risk of species. Here we parameterised an integral projection model, which allows studying how individual life histories determine population-level processes. Using bulb mites (Rhizoglyphus robini), a species that shows boom-bust dynamics, we assess the extent dispersal expression (frequency of disperser morphs) and dispersal probability (probability to emigrate) affect the proportion of dispersers and natal population growth rate. We find that, if residents and dispersers differ in life history, different combinations of dispersal probability and dispersal expression produce the same proportion of leaving dispersers. Additionally, for a given proportion of dispersing individuals different natal population growth rates occur. Dispersal life histories, and frequency of disperser morphs occurring in the natal population, can thus significantly affect population-level processes. It is therefore important for our understanding of boom-bust dynamics to elucidate how dispersal characteristics of individuals relate to population resilience and potential re-establishment for populations after a bust phase.