Linking behavioral type and cannibalism propensity in Eurasian Perch

Abstract

Consistent differences in behavior between individuals within a population can contribute to community and system complexity by adding alternate trophic linkages and maintaining diversity. Past studies have examined individual differences in behavior as well as the occurrence of cannibalism within populations, but not the link between predator behavioral type and cannibalism. Individual Eurasian perch Perca fluviatilis were assayed for sociability and activity, and a subset of individuals, selected based on individual consistency in activity levels, were included in predation experiments. These focal perch were each given an equal number of small conspecific and heterospecific (roach, Rutilus rutilus) prey, and recorded selective predation showed that the behavioral type characterized by low activity and sociability had a significantly higher cannibalism rate. This increased cannibalism could be due to inferior competitive ability among inactive and antisocial individuals, compared to their more active and social counterparts, in successfully capturing the quick swimming roach. Another possibility is that perch with differing activity levels use different hunting strategies that are more efficient in capturing different types of prey. Regardless of the cause, the link between predator behavioral type and cannibalistic behavior may be a mechanism important to the understanding of community and trophic processes in natural systems.

Popular Abstract

Fish are food, not friends

“Typical that the slow moving, anti-social fish are cannibals,” responded Nate, my best friend, when I told him about the results of my study. Humans are good at both thinking ourselves unique compared to other animals and imposing our societal values upon them (how else would Nemo meet a vegetarian great white shark). The background for my study somehow manages to be affected by both of these things. In part because of its scarcity among humans, early scientific literature neglected cannibalism or misinterpreted it as a rare or atypical behavior. Now recognized as remarkably widespread in the animal kingdom, it has been studied in birds, reptiles, spiders, mammals, and especially fish. Unlike cannibalism, individual differences in behavior, also called personality, are expected among humans and this phenomena was previous assumed to be exclusive to humans. Because of this false assumption, individual behavioral differences in animals, like cannibalism, were commonly misinterpreted as the result of study error. Only recently have studies begun examining the implications of individual differences in animals’ behavior.

Who eats whom and the relationship between the fish doing the eating and fish running away, has been studied for many years. Past studies show that prey that express one behavior over another, such as boldness over shyness, are preferred by predators. But if prey personality matters when examining who gets eaten, shouldn’t predator personality matter too? My study examines the relationship between predator behavioral type and cannibalism in a common freshwater fish, the Eurasian Perch.

To quantify personality in our predator fish we first tested activity and sociability by recording the total time each fish spent moving and the time they spent close to a small shoal of other perch. Each individual perch has a behavioral type (also called personality), which is a specific combination of activity level and time spent shoaling. I found two distinct groups of fish displaying opposite behavioral types, one group of highly active and highly social perch (High) and a second group of inactive and antisocial perch (Low). A small subset of fish was selected to act as predator fish in a prey selection experiment. Each predator perch was placed in a tank with five small roach and five small perch and allowed to feed at will until they had consumed three total prey fish.

The record of who ate whom shows that the antisocial and slow moving group was more cannibalistic while the active and social fish selectively ate roach, and avoided cannibalism. The higher cannibalism among low behavioral type perch could be a result of them being less efficient at catching the fast swimming roach, and settling for the slower-moving perch. Another possibility is that perch with differing activity levels use different hunting strategies that are more efficient in capturing different types of prey. Regardless of the cause, the difference in diet between predators with different behavioral types is important because it adds complexity to the system. Given the importance of cannibalism in many aquatic ecosystems it is important to continue studying the influence of both predator and prey behavior on predator diet and scale these findings up to better understand past changes in fish populations and how they may change in the future.

Advisor: Anders Nilsson
Master´s Degree Project 30 credits in Aquatic Ecology* 2016
Department of Biology, Lund University

• author: Andersson, Matilda
• supervisor: Anders Nilsson
• organization: Degree Projects in Biology
• course: BIOM01 20152
• year: 2016
• type: H2 - Master's Degree (Two Years)
• subject: Biology and Life Sciences
• language: English
• id: 8871160
• date added to LUP: 2016-04-18 09:53:47
• date last changed: 2016-04-18 09:53:47