Ecomorphological trait analysis as a risk assessment tool for invasive freshwater fish species

The invasive success of alien freshwater fish species is potentially enhanced by efficient food competition with native species. Competition between such trophic analogues has been studied using functional-response experiments, in which generally the invader outperformed the native species in terms of maximum consumption rate. However, the mechanisms and traits underlying these differences in functional responses are mostly not clear at the organismal level. In this study I used an ecomorphological approach (the Food-Fish Model: FFM) to investigate how differences in feeding performance may depend on feeding-associated morphological traits. The FFM explicitly links morphological traits of the predator to biomechanical, behavioral, and chemical characteristics of prey, resulting in trophic profiles quantifying the capacity of a species to feed on a range of aquatic prey types. It was expected that species with a higher predicted capacity of feeding on a particular prey type, would also show higher maximum consumption rates in functional-response experiments. To explore this, I compared a series of pairs of alien and native freshwater fish species with published different functional responses (e.g. alien Gobiidae and Centrarchidae v. native Cottidae and Cyprinidae), and measured 15-20 feeding-associated morphological traits, covering all stages of feeding, including prey detection, intake, chewing, and digestion. In case of prey types that set high demands on predators, such as tadpoles (a relatively large and fast prey), or mollusks (hard prey), the quantified feeding capacities based on morphology were generally in line with consumption rates, although the alien species were not necessarily better at all stages of the feeding process. Therefore, using feeding-associated morphological traits can lead to mechanistic insights into feeding and competition for prey, and thus is a promising additional tool for risk assessment of alien fishes, provides causal explanatory power.