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

Abstract

Whether the invasive freshwater cladoceran Bythotrephes longimanus can establish after introduction into a water body depends on several biotic and abiotic factors. Among these, water temperature is important because both development rates and mode of reproduction (parthenogenetic or sexual) in Bythotrephes are influenced by temperature. We built a stage-structured model for the population dynamics of Bythotrephes based on the temperature-dependency of events in its life cycle and used the density of resting eggs at the end of each year to track changes in population density. The model was parameterized using data from published laboratory experiments and data on the Bythotrephes population in Harp Lake, Canada, from 1994 to 2005. The parameterized model was then used to simulate the outcome of invasions with different initial resting egg densities under different temperature regimes. A strong Allee effect emerged from the model, i.e. there is a critical threshold density above which the population can establish and below which it goes extinct. We showed analytically that the existence of an Allee effect arises from the model structure and is therefore robust to the parameter values. An increase in temperature reduces the establishment threshold for introductions in the same year as well as for introductions in the previous years. We therefore hypothesize that climate warming might facilitate Bythotrephes invasions. Finally, we study how the establishment threshold is influenced by the timing of the introduction event and thus identify time periods during the year when lakes may be particularly susceptible to Bythotrephes invasions.

The spread, establishment and impacts of the spiny water flea, Bythotrephes longimanus, in temperate North America: a synopsis of the special issue

“…Potapov et al (2011), Wittmann et al (2011), and Brown and Branstrator (2011 all provide evidence for a strong Allee effect influencing Bythotrephes establishment success, (see also . Underlying mechanisms of Allee effects were also identified, in particular bottom-up control and starvation ) controlling summer population size, the rapid turnover and relative low survival rate of resting eggs (Brown and Branstrator 2011), and temperature-limited growth (Wittmann et al 2011), below thermal thresholds. Even relatively well established populations may fail in particularly hot years (Kerfoot et al 2011).…”

“…Here, we fill several fundamental holes in understanding about Bythotrephes. In terms of population and community dynamics, Brown and Branstrator (2011) and Wittmann et al (2011) demonstrate the role of the resting egg biology of Bythotrephes on its invasion success, while Pichlová-Ptácníková and Vanderploeg (2011), Bourdeau et al (2011), andYoung et al (2011), respectively, consider how differences in prey avoidance abilities, migration tendencies, and spring abundances can explain the invader's abundance, and its differential impacts on specific taxa. Hessen et al (2011) and Jokela et al (2011) compare the invader's interactions with native macro-invertebrate, holoplanktonic predators in Norway and Canada; Kerfoot et al (2011) prove the role of fish in its dispersal; while Rennie et al (2011) document the overall changes in trophic structuring of food webs that follow invasion.…”

“…Wittmann et al (2011) predict that small increases in temperature should increase the probability of establishment of Bythotrephes by increasing rates of population growth of founding propagules to Allee effect thresholds that will lead to establishment. However, Bythotrephes is a coolwater species, dying at temperatures just above 25°C (Grigorovich et al 1998;Yurista 1999;Kim and Yan 2010); hence, climate warming should eventually alter the invader's spread and its eventual distribution.…”

Effects of chemical and physical conditions on hatching success of Bythotrephes longimanus resting eggs

“…Because B. longimanus is invasive in North America (Lehman and Cá ceres 1993;Yan et al 2001;Pangle et al 2007), there has been considerable interest in understanding its life cycle and the role of the resting egg during range expansion (Brown and Branstrator 2011;Wittmann et al 2011). Human recreational equipment (e.g., bait bucket, boat hull, or fishing line) is believed to be the primary overland dispersal vector of B. longimanus Weisz and Yan 2010 (Grigorovich et al 1998), their efficacy at killing resting eggs has not been evaluated.…”

Can Daphnia lumholtzi invade European lakes?

“…In this case, the growing season would have to be sufficiently long and temperatures sufficiently warm to reach high population densities and to produce enough resting eggs that will hatch in the next year. Increases in temperature may thus promote D. lumholtzi establishment by helping them to overcome Allee effects, as has been suggested for another cyclical parthenogenetic cladoceran, Bythotrephes longimanus (Wittmann et al 2011).…”