Introduced species can cause localized extinctions, but they may also facilitate coexistence amongst prey species through top-down controls. In lakes across Aotearoa New Zealand, it is hypothesized that the native freshwater fishes kōaro/climbing galaxias (Galaxias brevipinnis) and smelt (Retropinna retropinna) are typically unable to coexist due to competitive exclusion of kōaro by smelt. Conversely, in lakes where introduced trout (Oncorhynchus mykiss) are also present kōaro can persist in the presence of smelt. This is likely due to top-down control of smelt populations by trout, allowing kōaro to escape competitive pressure. How the interactions between these three species play out is likely a function of lake productivity, environmental conditions, and the relative amount of littoral and pelagic habitat available.
Here, we will present an agent-based model (ABM) of a simple lake food web consisting of two competing species (kōaro and smelt) and a top predator (trout). Agent based models are powerful tools for examining food-web dynamics, particularly when individual variability and spatially explicit dynamics are of interest. These models also allow us to explore management and conservation interventions, such as the effect of total, or partial removal of non-native species. We will use our ABM to explore food web dynamics among trout, kōaro and smelt. We will examine how prey preference, habitat availability, and lake productivity influence persistence and coexistence.