Predators, Prey, and Anglers : Behavioral Mechanisms Driving Vulnerability and Selection in Freshwater Ecosystems

Abstract

Predator-prey interactions are important processes that shape ecological communities. Because predation exerts strong selective pressures, invasive species and anthropogenic influences that change these interactions may strongly affect native fish populations. In this dissertation, consisting of three scientific peer-reviewed manuscripts, the influence of developmental stages in prey and behavioral traits of predators on susceptibility to predation and capture in freshwater ecosystems is studied using a combination of laboratory, mesocosm, and field experiments. In paper I, stereoscopic 3D video analyses were used to investigate predator-prey interactions between invasive three-spined stickleback (Gasterosteus aculeatus) and native prey fish larvae. The analysis revealed that capture success of different age-classes of predator-naïve prey fish larvae is not related to parameters of prey swimming performance, but to ontogenetic differences in escape timing and escape complexity of prey. In paper II, pike (Esox lucius) were observed under standardized laboratory conditions using an advanced 3D video setup to assess behavioral types or coping strategies and their effects on catchability in angling, bait selectivity, hunting behavior, and learning. This study showed consistent individual differences in proactive and reactive coping styles that are related to their vulnerability to angling, with proactive individuals being more vulnerable to angling than reactive individuals. It was also shown that learning plays a major role in the development of susceptibility to angling: pike of both behavioral types quickly learned to avoid bait. In paper III, these findings were tested in a natural ecosystem using underwater video cameras during trolling that were specially designed for angling, where fast and slow attacking pike were tested in a standardized foraging trial. The study confirmed that the individual variation in coping styles found in laboratory observations could also be identified in the wild. The study showed that pike with a more, proactive coping style were caught more often on artificial lures compared to their reactive conspecifics. The overall higher susceptibility of proactive animals to capture together with bait-dependent selection pressure may result in a significant effect of angling on the behavioral diversity in pike populations. Together, the three studies demonstrate the role that finely tuned behavioral mechanisms play in natural and human-induced predatorprey interactions. It is therefore important to include behavioral diversity in studies of ecological resilience and as a relevant component of biodiversity to be considered in management decisions related to fisheries and conservation of fragile freshwater ecosystems.