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Abstract

In Lake Lucerne, Switzerland, the predaceous cladocerans Leptodora kindti and Bythotrephes longimanus segregate along spatial and temporal dimensions. In spring (April-May/June), Bythotrephes longimanus occurs below 0-20 m, while Leptodora is absent. In summer and early autumn (July-September/October), when Leptodora dominates during daytime in the 0-20 m depth, Bythotrephes longimanus also lives in deeper zones. Food competition and fish predation pressure may be the cause of differences in ecology of Leptodora and Bythotrephes acquired during evolution. Due to its transparency and tolerance of higher temperature, Leptodora could avoid fish predation and, therefore, competes with Bythotrephes longimanus successfully. In addition, the differences between the two species may account for the spatial and temporal niche segregation in oligotrophic Swiss Lakes. But spatial niche segregation is less important in mesotrophic lakes with high prey density than in oligotrophic lakes with low prey density. In small, eutrophic lakes importance of temporal niche segregation also decreases, and Bythotrephes is seldom or not present. The preference of Bythotrephes to live in deeper water to avoid fish predation during summer may be the cause of its difficulties to establish itself in small and eutrophic lakes with high prey densities, where the hypolimnion is missing or anoxic. In the spring, Bythotrephes exhibits r-strategy (smaller body size and a higher fecundity), the female is already fertile after the first molt. In the summer, a K-strategy prevails (larger body length and lower fecundity than in the spring), and female Bythotrephes are fertile only after the second molt. Shortage of prey (biomass of Bosmina and Daphnia decreased after June especially in the surface layers) and the maximum fish predation pressure in summer may change the life strategy of Bythotrephes: while fecundity decreases from generation to generation, body length increases. Enhanced prey densities (e.g. during mesotrophic conditions in L. Lucerne) lead to larger individuals in summer and autumn.

Shifting invertebrate zooplanktivores: watershed-level replacement of the native Leptodora by the non-indigenous Bythotrephes in Canadian Shield lakes

“…Although it has been predicted that co-existence of the two predators is unlikely in Canadian Shield lakes (Branstrator 1995;Foster and Sprules 2009), and classic theory suggests competitive exclusion (Hardin 1960), it has long been known that many plankton species with overlapping niches can co-exist (Hutchinson 1961). Nevertheless, if Bythotrephes is experiencing competitive and/or enemy release due to its change in locale (Elton 1958), increased prey consumption by Bythotrephes could negatively effect native Leptodora populations. In addition, Leptodora itself can fall prey to Bythotrephes, while the reverse does not seem to be the case, as even small Bythotrephes are too large for the grasping basket of Leptodora (Branstrator 1995;Herzig and Auer 1990).…”

Food web consequences of size‐based predation and vertical migration of an invertebrate predator (Leptodora kindtii)

“…Leptodora is a voracious predator of small-to medium-sized zooplankton (Andrews 1948;Herzig and Auer 1990) and is thought to have strong effects on the abundance (Hall 1964;Herzig 1995;Uusitalo et al 2003), seasonality (Costa and Cummins 1969;Herzig 1995), and composition of zooplankton communities (Lane 1979;Yan et al 2002;McNaught et al 2004). Although Leptodora densities are influenced by macro-invertebrate predators such as Bythotrephes in boreal lakes (Weisz and Yan 2011), this taxon remains an important predator in productive European and North American lakes (Enz et al 2001;Palmer et al 2001) where Bythotrephes abundance has declined because of eutrophication (Therriault et al 2002). Despite Leptodora's wide distribution and potentially strong effects on lake food webs, very little is known about what factors explain variation in Leptodora density, habitat use, feeding behavior, and size structure.…”