Intraspecific variation and the leaping ability of northern pike (Esox lucius): implications for invasion ecology and management

Abstract

Although biological invasions are a leading threat to global biodiversity they provide opportunities to study factors that mediate invasion success from ecological and evolutionary perspectives and inform management efforts. The invasion of Northern Pike (Esox lucius) throughout southcentral Alaska has provided a useful case study, where invasive Northern Pike may benefit relative to native individuals due to high habitat suitability, abundant fish prey, and adaptive or plastic selective forces of invasion. Northern Pike continue to spread throughout the highly interconnected river and lake systems of southcentral Alaska; however, hypothesized differences in Northern Pike and native salmonid leaping abilities make selective vertical drop barriers a potential management option. Here, I build upon previous work by comparing physiological and morphological traits of invasive and native Northern Pike from river and lake habitats in Alaska that may influence their invasion success and leaping ability. Then, I used leaping experiments to determine how physical (abiotic) factors and individual biological traits influenced the maximum leaping ability of Northern Pike and developed a model to characterize these relationships. I found that invasive Northern Pike stomachs were two times more likely to contain energy-rich vertebrate diet items relative to native individuals, which was associated with two-fold faster growth rates, earlier ages-at-maturity, and 30% greater lipid content. Diet and physiological benefits were greater in lake habitats for invasive individuals, while native individuals experienced improved metrics in river habitats, potentially explained by thermal regimes, metabolic demands, and food availability. Leaping experiments proved that Northern Pike could ascend barrier heights four-times greater than previously assumed; pool depth, body size, and standardized growth rate also influenced individual leap success. Northern Pike leaping ability was significantly lower than salmonids. However, model predictions suggest that faster growth rates of invasive Northern Pike in Alaska may marginally enhance their leaping ability, and barriers should be tested in-situ before implementation. Insights into Northern Pike physiology and leaping behavior that result from this work can help managers determine if Northern Pike-selective barriers are a viable option in southcentral Alaska and elsewhere Northern Pike are invasive, and supports the importance of intraspecific variation in invasive species ecology and management.