Impact of food concentration on diel vertical migration behaviour of Daphnia pulex under fish predation risk

Abstract

Vertical migration of Daphnia represents the best-studied predator-avoidance behaviour known; yet the mechanisms underlying the choice to migrate require further investigation to understand the role of environmental context. To investigate the optimal habitat choice of Daphnia under fish predation pressure, first, we selected the individuals exhibiting strong migration behaviour. The animals collected from the hypolimnion during the daytime were significantly larger, being more conspicuous, and in turn performed stronger diel vertical migration (DVM) when exposed to fish cue. We called them strong migrants. Second, we provided the strong migrant D. pulex with food at high and intermediate (1 and 0.4 mg C l -1 , respectively) levels, which were well above the incipient limiting level and of high quality. They traded the benefits of staying in the warm water layer and moved down to the cold water in response to fish cue indicating fish predation. The availability of food allowed the animals to stay in the cold hypolimnion. However, at the low food level (0.1 mg C l -1 ), which is an additional constraint on fitness, Daphnia moved away from the cold hypolimnion. Poor food condition resulted in strong migrant Daphnia to cease migration and remain in the upper warmer water layer. Although temperature is known to be a more important cost factor of DVM than food, our results clearly show that this is only true as long as food is available. It becomes clear that food availability is controlling the direction of vertical positioning when daphnids experience a dilemma between optimising temperature and food condition while being exposed to fish cue. Then they overlook the predation risk. Thus, the optimal habitat choice of Daphnia appears to be a function of several variables including temperature, food levels and fish predation.

Seasonal adaptations of Daphnia pulicaria swimming behaviour: the effect of water temperature

“…Recent modelling studies (Schalau et al, 2008) demonstrate that temperature is the key environmental factor driving interannual variability in Daphnia populations, while mesocosm evidence (Beklioglu et al, 2008) indicates temperature as the primary driver of diel vertical migrations as long as food is not limiting.…”

Use of deep autochthonous resources by zooplankton: Results of a metalimnetic addition of 13C to a small lake

“…Patterns of diel vertical migration in zooplankton are the result of predator avoidance, competition for resources, and thermal requirements for growth and reproduction (Lampert 1989). In lakes with primary production in the metalimnion, zooplankton that migrate deep in the water column during the day can potentially exploit resources that can be rich in phosphorus (Sterner and Schwalbach 2001), thereby aiding growth (DeMott et al 2004) while avoiding visual predators such as fish (Beklioglu et al 2008). However, the cold water within the thermocline can significantly slow zooplankton growth and reproduction rates (Loose and Dawidowicz 1994).…”

Diel Vertical Migration of zooplankton in a eutrophic bay of Lake Victoria

“…In the absence of predation, zooplankton will distribute themselves in a water column according to the availability of food resources (Lampert et al, 2003), with other factors like competition (Larsson, 1997) contributing to their distribution to maximize fitness. The choice for an optimal habitat may therefore be a function of several factors including temperature, food availability and predation (Beklioglu et al, 2008).…”