Differential short- and long-term effects of an invertebrate predator on zooplankton communities in invaded and native lakes
Correspondence: Noreen E. Kelly, Department of Biology, York University, 4700 Keele St., Toronto, ON M3J 1P3, Canada.
Forecasting the effects of invasive species remains difficult, because short-term effects may be transitory and theories of long-term effects are poorly developed and rarely tested. Here, we compare zooplankton communities from freshwater lakes in Norway and Canada that differ in their duration of exposure to the invertebrate predator Bythotrephes longimanus, to aid in predicting its potential long-term impacts on Canadian zooplankton communities.
Freshwater lakes in Canada and Norway.
We compared differences in zooplankton community structure, richness and occurrence between lakes with and without Bythotrephes in Canada and Norway using univariate and multivariate analyses of the incidence of crustacean zooplankton species.
Correspondence analysis confirmed that zooplankton community composition differed dramatically in lakes with and without Bythotrephes in Canada but not in Norway. The short-term exposure of Canadian lakes to Bythotrephes led to lower zooplankton diversity, particularly for cladoceran species, whereas in Norway, a greater diversity of zooplankton, particularly for copepod species, occurred in lakes where Bythotrephes has been present for long periods. Significantly more species in Norway demonstrated an increase in their frequency of occurrence, while significantly more species in Canada demonstrated a decrease, in lakes containing Bythotrephes.
Bythotrephes can modify zooplankton community structure, diversity, and spatial occurrence across a watershed in a short period (i.e. a few decades) after invasion; however, some species appear to adapt to the presence of Bythotrephes over time. We hypothesize the long-term effects of higher diversity in Norwegian lakes is attributed to altered interspecific community interactions, coupled with behavioural adaptations to avoid Bythotrephes predation, enabling the remaining species to increase their populations in space and time. If Canadian communities adapt similarly, the long-term effects of Bythotrephes invasion in Canada may thus be less severe than those observed in the first few decades of the invasion.