Food‐web‐mediated effects of climate warming: consequences for the seasonal Daphnia dynamics

Abstract

Summary 1. In an extensive field study, we tested the hypothesis that warming during a sensitive period alters trophic interactions in pelagic food webs of dimictic lakes: Matching of predation on the key herbivore Daphnia by vertebrate (Perca fluviatilis) and invertebrate (Leptodora kindtii) predators would destabilise Daphnia populations during summer. To predict food‐web‐mediated effects of climate warming, we relied on phase‐specific warming trends (during winter, early thermal stratification, summer stagnation) of an 11‐year (1999–2009) period to study instantaneous or time‐delayed ecological responses. 2. Warming during the period of early thermal stratification (here corresponding to May) rather than during winter or summer was found to generate complex, time‐delayed cascading effects on Daphnia via timing and rates of predation. In contrast to our hypothesis, warming exceeding a critical mean temperature (14 °C) during May increased the stability of the Daphnia population during summer. 3. The termination of predation on Daphnia by older perch and L. kindtii was advanced even stronger (14 days per degree Celsius warming during May) than the start of predation. Warming during May thus shortened the period of synchronised predation on Daphnia by older perch, young‐of‐the‐year perch and L. kindtii (match index) by up to 4 weeks, thereby decreasing total rates of predation on Daphnia during July by up to 40%. 4. The timing of the top‐down control of Leptodora dynamics by perch proved to be a key process for population stability of Daphnia during summer compared to the less important direct cascading effect of fish on Daphnia and temperature effects on Leptodora growth and consumption or on Daphnia reproduction. 5. We conclude that predicting the consequences of climate warming for plankton dynamics requires a mechanistic understanding of lake‐specific temperature‐driven changes in trophic cascades, especially when an invertebrate predator is dynamically coupled both to the key herbivore and to their predators.

The response of temperate aquatic ecosystems to global warming: novel insights from a multidisciplinary project

“…The interplay between temperature, stratification, and light was also the focus of the limnetic mesocosm experiments on Brunnsee (Sebastian et al 2012), highlighting the role of thermal stratification as light switch. Phenological shifts in zooplankton key species and fish larvae have also been demonstrated in field studies (Hüls-mann et al 2012;Wagner et al 2012b). The spring increase in the grazing pressure by herbivorous zooplankton is not necessarily a numerical response to elevated food levels.…”

“…Biotic interactions as modulators of climate change effects have been reported from several AQUASHIFT projects (Burgmer and Hillebrand 2011;Dziallas and Grossart 2012;Gaedke et al 2010;Klauschies et al 2012;Sommer and Lewandowska 2011;Wagner and Benndorf 2007;Wagner et al 2012b) as well as from terrestrial ecosystems (Suttle et al 2007). For two-link food chains, it is easy to predict an increasing disadvantage for the prey, if the predator profits more strongly from warming than the prey.…”

“…In the case of the Saidenbach reservoir, Daphnia phenological patterns were found to be independent of winter conditions (Hüls-mann et al 2012). Rather, they depended on warming during early stratification, which was also the critical period for hatching and early growth of fish (Wagner and Benndorf 2007;Wagner et al 2012b).…”

“…For the Daphnia-phytoplankton interaction, modeling studies suggest that a mismatch is only likely to occur under extreme warming and a strong reliance of Daphnia dynamics on recruitment from resting eggs, triggered by day length (De SenerpontDomis et al 2007). In the Saidenbach Reservoir study, climate-driven phenology shifts of the participant species led to a switch between invertebrate and fish predation on the herbivorous zooplankton (Wagner and Benndorf 2007;Wagner et al 2012b). Simulations based on field and laboratory data showed that an increase of environmental temperature has the potential to cause a decoupling of the life cycle of Gammarus pulex and the availability of its food resource leaf litter in temperate streams Kupisch et al 2012).…”

Zooplankton biomass dynamics in oligotrophic versus eutrophic conditions: a test of the PEG model

“…While a stronger control by temperature as compared to food limitation of zooplankton spring dynamics might be expected from previous studies on Daphnia dynamics (Gillooly & Dodson, ; George, ; Straile et al ., ; Wagner et al ., ), the absence of a clear effect of trophic status on biomass peak timing seems at first surprising. Although modelling (Schalau et al ., ) and mesocosm (Berger et al ., , ) studies support the importance of food limitation on Daphnia spring phenology, in addition to the effect of temperature, these studies addressed the effect of food limitation, rather than the effect of trophic status of the lake.…”