Do feeding-related functional traits predict the invasive success of alien freshwater fishes?

Summary

Successful invasions of alien freshwater fish species are potentially enhanced by efficient food competition with native species. Such competition can be apparent from functional-response experiments, in which generally invaders outperform native species. However, it is mostly unclear which traits drive these differences at the organismal level. Here I will illustrate an ecomorphological approach in which feeding-associated morphological traits of individual fishes will be linked to biomechanical, behavioural, and chemical characteristics of a range of aquatic prey types, leading to quantified feeding capacities of the fish species. I compared alien and native freshwater fish species from the Netherlands (Gobiidae, such as round goby, v. Cottidae, e.g. river bullhead) and South Africa (Centrarchidae, such as smallmouth bass v. native Anabantidae, e.g. Cape kurper), and measured 15-20 feeding-associated morphological traits, covering all stages of feeding, including prey detection, intake, chewing, and digestion. In general, quantified feeding capacities based on morphology were generally in line with actual diets, especially for demanding food types, such as very hard (molluscs) or fast (fish) prey. Alien species were not necessarily direct competitors of native species, but also appeared to be able to fill hitherto ‘vacant niches’.