Life History and Multiple Antipredator Defenses of an Invertebrate Pelagic Predator, Bythotrephes longimanus

Abstract

Abstract. Multiple antipredator defense strategies and their interactions were examined in a field study of the predatory planktonic waterflea Bythotrephes longimanus in Lake Constance, at the northern fringe of the European Alps. Because of its large body size and conspicuousness, Bythotrephes is a preferred prey of freshwater fish. We observed seasonal changes in life history and morphology and diel vertical migration, all best understood as a response to fish predation. Bythotrephes population dynamics were characterized by pronounced population growth in late spring, maximum abundances in June, and a steady decline toward the end of the season. In late spring, high population growth rates were achieved by means of large clutches, low investment in individual offspring, and small size at first reproduction. While the population was still increasing, a marked life history shift occurred. The reproductive strategy of females switched toward high per-offspring allocation at the expense of clutch size. This change in reproductive behavior resulted in an increase in the size of neonates and was accompanied by an increase in the size at first reproduction. Such a life history shift is typically observed in the presence of gape-limited predators, which points to the importance of juvenile fish as the principal vertebrate planktivores in Lake Constance. The length of Bythotrephes defensive spina increased throughout the season, reflecting increasing predation pressure, probably owing to seasonally increasing mouth gape size of juvenile fish. In contrast to the predictions of the predator-avoidance theory, the migration amplitude of large and conspicuous Bythotrephes was small as compared to other zooplankton species. We argue that theory and data can be reconciled if the migration behavior of Bythotrephes is considered as a result of an interaction of predator defenses in the presence of predominantly juvenile, gape-limited fish. As Bythotrephes achieved protection because of its life history and spina, the costs of large diel migrations may outweigh the benefits.

Temperature-dependent Allee effects in a stage-structured model for Bythotrephes establishment

“…The question how environmental factors like temperature, starvation, crowding and photoperiod act together to determine the sex of cladocerans has mainly been studied in Daphnia thus far and is not well understood yet (Hobaek and Larsson 1990;Eads et al 2008). Some males can be observed in summer, but male production peaks in autumn when water temperatures go down (Straile and Hälbich 2000). At about the same time, mature females start to undergo an anatomical transformation that enables them to produce meiotic resting eggs after internal fertilization by males (Egloff et al 1997).…”

Increased abundance of the non-indigenous zooplanktivore, Bythotrephes longimanus, is strongly correlated with greater spring prey availability in Canadian Shield lakes

“…In Peninsula Lake in 2004, which had a very similar early spring Bythotrephes abundance peak to 2003, per capita birth rates were highest in June, and prey availability was the greatest contributor on 3 June. Bythotrephes in European Lake Constance (Straile and Hälbich 2000) and Lago Maggiore (Manca et al 2007) have a similar population dynamic to Peninsula Lake. The early spring Bythotrephes abundance peaks in these lakes were also attributed to earlier onsets of exponential growth (Manca et al 2007) and high springtime per capita birth rates (Straile and Hälbich 2000).…”

“…A greater availability of prey in the early months of Bythotrephes emergence would allow for higher per capita birth rates, leading to increased population growth. Additionally, Bythotrephes clutch sizes in the spring are much larger than the summer, making very high birth rates possible (Straile and Hälbich 2000;Young 2008). In Peninsula Lake in 2004, which had a very similar early spring Bythotrephes abundance peak to 2003, per capita birth rates were highest in June, and prey availability was the greatest contributor on 3 June.…”

Patterns of Bythotrephes longimanus distribution relative to native macroinvertebrates and zooplankton prey

“…Based on the predator-avoidance hypothesis (Lampert 1993), we would expect a strong diel vertical migration by Bythotrephes given its conspicuousness to visual predators. Its relatively weak migration and shallow daytime position (Dokulil et al 1990;Lehman and Caceres 1993;Grigorovich et al 1998;Straile and Halbich 2000) may be a result of the type of planktivore pressure it experiences, where coldwater Coregonus spp. represent an important source of mortality for Bythotrephes (De Bernardi and Giussani 1975;Coulas et al 1998;Palmer et al 2001).…”

“…Moreover, simple co-occurrence at the lake scale does not necessarily mean that ecologically significant spatial overlap or interaction is occurring. Many macroinvertebrate predators exhibit diel vertical migration (DVM) as a means of reducing predation risk (Lampert 1993); however, Bythotrephes does not display a strong DVM in its invaded range, remaining relatively high in the water column during the day (Lehman and Caceres 1993;Straile and Halbich 2000;Young and Yan 2008). Although this may reduce the amount of vertical overlap between Bythotrephes and some of the native macroinvertebrates, it could still have an important effect, especially in terms of food availability.…”