How does behaviour underpin the impact of invasive tilapia on native fish?

Invasive species have a huge impact on the structure of freshwater communities and are a major source of biodiversity loss. Physiological, morphological and life history traits that are associated with invasive potential have been studied extensively. How invasive and native species interact through behaviour, however, has rarely been documented, particularly in aquatic habitats where observing behaviour is problematic. Aquaculture using Nile tilapia Oreochromis niloticus is growing exponentially throughout the tropics as an affordable source of animal protein; however, its spread is associated with feral populations becoming established outside its native range and subsequent negative effects on native fish assemblages. Many of these negative effects are hypothesised to be mediated by behaviour: Nile tilapia are believed to competitively exclude native fish from shelters (exposing native fish to greater predation risk), outcompete native fish for food, and their foraging behaviour reduces macrophyte algae abundance and increases water turbidity. Despite some evidence of these effects, e.g. from behavioural laboratory studies, observing and quantifying the extent to which they occur in natural systems has remained elusive. This project will use artificial shelters equipped with underwater cameras in mesocosms and at field sites in Tanzania to quantify in unprecedented detail the interactions between Nile tilapia, an increasingly problematic invasive species in tropical freshwater ecosystems, and native cichlid fish species.