Food limitation impacts life history of the predatory cladoceran Bythotrephes longimanus, an invader to North America

Abstract

North American invasions of the predatory cladoceran Bythotrephes longimanus have resulted in declines in native zooplankton abundance, species richness, and diversity. In the field, population maxima of Bythotrephes are positively correlated to those of their zooplankton prey. To test the hypothesis that increased prey availability enhances Bythotrephes fitness, we reared Bythotrephes in the laboratory on three mixed-species prey densities (equivalent to 15, 30, and 45 prey organisms day-1; designated “low,” “medium,” and “high” food treatments, respectively) over 22 days at 21°C. Bythotrephes consumed the daily equivalent of 9, 14, and 22 prey organisms at the low, medium, and high food densities. Smaller, slower prey were most often selected. Indeed, with increasing prey density, Bythotrephes’ predation rates increased, resulting in significantly higher population growth rates, net reproductive rates, growth, and first brood clutch and offspring sizes; significantly faster generation times; and shorter maximum life spans. We propose that the positive relationship between Bythotrephes population maxima and prey seen in the field is largely due to increased predation rates by Bythotrephes when prey abundance is high and the fitness benefits that ensue. Our findings may be useful for Bythotrephes risk and impact assessments.