Larger risk-taking by non-native than native shrimp: an advantage in a human-disturbed environment?

Abstract

The invasion of foreign species into ecosystems is a growing problem. To control their spread and population growth, knowledge is needed on the factors that facilitate or impede their invasion success. Traits often associated with invasion success are high activity, boldness, and aggression. However, these traits also make invaders more susceptible to predation, which could curb their population growth. We investigated if a recent invader into the Baltic Sea, the shrimp Palaemon elegans, differs in risk-taking from a native shrimp, P. adspersus, regarding activity, habitat choice, and response to perceived predation threat. We found the invading shrimp to take larger risks than the native shrimp; it did not adjust its behaviour – activity, aggression, and foraging – to habitat structure, while the native shrimp did, and it resumed normal activity after a perceived predation threat sooner than the native shrimp. Despite the greater risk taking, the non-native shrimp population has grown rapidly during the last two decades and is now larger than the native one. We discuss plausible explanations for the population growth, including the recent decline in predatory fishes that could have reduced the cost of risk-taking, and anthropogenic eutrophication that has increased the abundance of food and could have allowed the population growth. Thus, human-induced changes to the environment may have altered the costs and benefits of risk-taking and benefitted the non-native shrimp. These results stress the need to assess the impact of human-induced environmental changes on optimal behaviour when evaluating the factors that influence invasion success in disturbed environments.