A matter of timing: heat wave impact on crustacean zooplankton

1. Climate change has affected zooplankton phenology and abundance in many freshwater ecosystems. The strong temperature anomalies that characterise summer heat waves make these events particularly suitable to study the effects of different seasonal warming patterns on zooplankton. Since heat waves are expected to occur more frequently under continuing climate change, they may also allow us to investigate how freshwater systems will be affected in the future. 2. Using a long‐term data set (1991–2007) from a shallow, eutrophic lake in Germany, we identify time periods in spring and summer during which cyclopoid copepods and bosminids are particularly sensitive to changes in water temperature. Based on this knowledge, we consider why summer populations responded differently to recent heat wave events that occurred at different times in the season. 3. Linear regressions of moving averages suggested that water temperatures shortly before and shortly after the clear‐water phase (CWP) were crucial for summer development of bosminids and cyclopoid copepods, respectively. Algal food availability (diatoms and cryptophytes) in the first weeks after the CWP also strongly influenced the summer populations of the two zooplankton groups. 4. Inter‐annual differences in water temperature during the critical time periods at least partly explained the contrasting responses of cyclopoid copepods and bosminids to heat wave events. 5. Our findings indicate that the zooplankton response to climate warming, particularly to heat wave events, is critically dependent on the temporal pattern of elevated water temperatures. Beyond that, we show that the summer zooplankton populations react to periods of warming in relation to events in the plankton annual cycle (such as the CWP in eutrophic lakes) rather than to warming at a fixed time in the season.     

The role of light for fish–zooplankton–phytoplankton interactions during winter in shallow lakes – a climate change perspective

1. Variations in the light regime can affect the availability and quality of food for zooplankton grazers as well as their exposure to fish predation. In northern lakes light is particularly low in winter and, with increasing warming, the northern limit of some present-day plankton communities may move further north and the plankton will thus receive less winter light.
2. We followed the changes in the biomass and community structure of zooplankton and phytoplankton in a clear and a turbid shallow lake during winter (November–March) in enclosures both with and without fish and with four different light treatments (100%, 55%, 7% and <1% of incoming light).
3. In both lakes total zooplankton biomass and chlorophyll- a were influenced by light availability and the presence of fish. Presence of fish irrespective of the light level led to low crustacean biomass, high rotifer biomass and changes in the life history of copepods. The strength of the fish effect on zooplankton biomass diminished with declining light and the effect of light was strongest in the presence of fish.
4. When fish were present, reduced light led to a shift from rotifers to calanoid copepods in the clear lake and from rotifers to cyclopoid copepods in the turbid lake. Light affected the phytoplankton biomass and, to a lesser extent, the phytoplankton community composition and size. However, the fish effect on phytoplankton was overall weak.
5. Our results from typical Danish shallow eutrophic lakes suggest that major changes in winter light conditions are needed in order to have a significant effect on the plankton community. The change in light occurring when such plankton communities move northwards in response to global warming will mostly be of modest importance for this lake type, at least for the rest of this century in an IPCC A2 scenario, while stronger effects may be observed in deep lakes.     

Effects of simulated heat waves on an experimental plant–herbivore–predator food chain

Greater climatic variability and extreme climatic events are currently emerging as two of the most important facets of climate change. Predicting the effects of extreme climatic events, such as heat waves, is a major challenge because they may affect both organisms and trophic interactions, leading to complex responses at the community level. In this study, we set up a simple three‐level food chain composed of a sweet pepper plant, Capsicum annuum; an aphid, Myzus persicae; and a ladybeetle, Coleomegilla maculata, to explore the consequences of simulated heat waves on organism performance, trophic interactions, and population dynamics. We found that (1) heat waves do not affect plant biomass, significantly reduce the abundance and fecundity of aphids, and slightly affect ladybeetle developmental time and biomass, (2) heat waves decrease the impact of ladybeetles on aphid populations but do not modify the effect of aphids on plant biomass, and (3) food chains including predatory ladybeetles are more resistant to heat waves than a simple plant–aphid association, with aphid abundance being less influenced by heat waves in the presence of C. maculata. Our results suggest that more biodiverse ecosystems with predators exerting a strong biotic control are likely to be less influenced by abiotic factors and then more resistant to extreme climatic events than impoverished ecosystems lacking predators. Our study emphasizes the importance of assessing the effects of climatic change on each trophic level as well as on trophic interactions to further our understanding of the stability, resilience, and resistance of ecological communities under climatic forcing.     

Climate warming and heat waves affect reproductive strategies and interactions between submerged macrophytes

Extreme climatic events, such as heat waves, are predicted to increase in frequency and intensity during the next hundred years, which may accelerate shifts in hydrological regimes and submerged macrophyte composition in freshwater ecosystems. Since macrophytes are profound components of aquatic systems, predicting their response to extreme climatic events is crucial for implementation of climate change adaptation strategies. We therefore performed an experiment in 24 outdoor enclosures (400 L) separating the impact of a 4 °C increase in mean temperature with the same increase, that is the same total amount of energy input, but resembling a climate scenario with extreme variability, oscillating between 0 °C and 8 °C above present conditions. We show that at the moderate nutrient conditions provided in our study, neither an increase in mean temperature nor heat waves lead to a shift from a plant‐dominated to an algal‐dominated system. Instead, we show that species‐specific responses to climate change among submerged macrophytes may critically influence species composition and thereby ecosystem functioning. Our results also imply that more fluctuating temperatures affect the number of flowers produced per plant leading to less sexual reproduction. Our findings therefore suggest that predicted alterations in climate regimes may influence both plant interactions and reproductive strategies, which have the potential to inflict changes in biodiversity, community structure and ecosystem functioning.     

The relation between the feeding activity of wintering shovelers (Anas clypeata) and the horizontal distribution of zooplankton in Lake Teganuma,Japan

We investigated seasonal changes in the number and feeding activity of Shovelers wintering in Lake Teganuma in connection with temporal and horizontal fluctuations of zooplankton, and analyzed esophageal contents of a captured Shoveler. Zooplankton community was dominated by rotifers followed by copepods during the study period. Horizontal distribution of both invertebrate taxa differed; rotifers most abundant in the western and eastern parts of the lake in February–March, and cyclopoid copepodids and nauplii more common in the northeast area of the eastern portion of the lake. The number and feeding activity of Shovelers increased from January to March in the northeast area of Lake Teganuma. A Shoveler captured in the area had mostly consumed cyclopoid copepodids despite the fact that rotifers dominated in the zooplankton community at that location. These results suggest that the horizontal distribution and feeding activity of the Shovelers were correlated with the distribution of the cyclopoid copepodids.     

Zooplankton Communities in the Shallow Lake Guiers (Senegal,West Africa)

Seasonal variations of zooplankton communities and their interactions with phytoplankton and environmental parameters were studied over a twelve‐month period in Lake Guiers (Senegal, West Africa). Zooplankton was most abundant during the warm and rainy season corresponding to the flood event (July to October) with peaks for rotifers and cyclopoid copepods in July–August and September–October, respectively. Filamentous cyanobacteria were the dominant phytoplankton during the warm season (August to November), while diatoms were dominant during the cool season (December to April). Temperature increase and river flooding both played an important role in these successions, favoring intense development of cyanobacteria and cyclopoid copepods. Trophic interactions also seem to be an important factor in structuring of the plankton community. Overall, the plankton composition displayed a trend toward a eutrophication state. Our study confirms the existence of seasonality in zooplankton communities and the importance of using biological indicators such as phyto‐ and zooplankton to monitor water quality, in particular in tropical freshwater ecosystems. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Freshwater Copepods and Rotifers: Predators and their Prey

Three main groups of planktonic animals inhabit the limnetic zone of inland waters and compete for common food resources: rotifers, cladocerans and copepods. In addition to competition, their mutual relationships are strongly influenced by the variable, herbivorous and carnivorous feeding modes of the copepods. Most copepod species, at least in their later developmental stages, are efficient predators. They exhibit various hunting and feeding techniques, which enable them to prey on a wide range of planktonic animals from protozoans to small cladocerans. The rotifers are often the most preferred prey. The scope of this paper is limited to predation of freshwater copepods on rotifer prey. Both cyclopoid and calanoid copepods (genera Cyclops, Acanthocyclops, Mesocyclops, Diacyclops, Tropocyclops, Diaptomus, Eudiaptomus, Boeckella, Epischura and others) as predators and several rotifer species (genera Synchaeta, Polyarthra, Filinia, Conochilus, Conochiloides, Brachionus, Keratella, Asplanchna and others) as prey are reported in various studies on the feeding relationships in limnetic communities. Generally, soft-bodied species are more vulnerable to predation than species possessing spines or external structures or loricate species. However, not only morphological but also behavioural characteristics, e.g., movements and escape reactions, and temporal and spatial distribution of rotifer species are important in regulating the impact of copepod predation. The reported predation rates are high enough to produce top-down control and often achieve or even exceed the reproductive rates of the rotifer populations. These findings are discussed and related to the differences between the life history strategies of limnetic rotifer species, with their ability to quickly utilize seasonally changing food resources, and adjust to the more complicated life strategies of copepods.     

Future recovery of baleen whales is imperiled by climate change

Historical harvesting pushed many whale species to the brink of extinction. Although most Southern Hemisphere populations are slowly recovering, the influence of future climate change on their recovery remains unknown. We investigate the impacts of two anthropogenic pressures—historical commercial whaling and future climate change—on populations of baleen whales (blue, fin, humpback, Antarctic minke, southern right) and their prey (krill and copepods) in the Southern Ocean. We use a climate–biological coupled “Model of Intermediate Complexity for Ecosystem Assessments” (MICE) that links krill and whale population dynamics with climate change drivers, including changes in ocean temperature, primary productivity and sea ice. Models predict negative future impacts of climate change on krill and all whale species, although the magnitude of impacts on whales differs among populations. Despite initial recovery from historical whaling, models predict concerning declines under climate change, even local extinctions by 2100, for Pacific populations of blue, fin and southern right whales, and Atlantic/Indian fin and humpback whales. Predicted declines were a consequence of reduced prey (copepods/krill) from warming and increasing interspecific competition between whale species. We model whale population recovery under an alternative scenario whereby whales adapt their migratory patterns to accommodate changing sea ice in the Antarctic and a shifting prey base. Plasticity in range size and migration was predicted to improve recovery for ice‐associated blue and minke whales. Our study highlights the need for ongoing protection to help depleted whale populations recover, as well as local management to ensure the krill prey base remains viable, but this may have limited success without immediate action to reduce emissions.     

Feeding convergence in South American and African zooplanktivorous cichlids Geophagus brasiliensis and Tilapia rendalli

Synopsis Acará, Geophagus brasiliensis, and red-breasted bream, Tilapia rendalli, are important planktivorous cichlids in southern Brazilian lakes and reservoirs. In laboratory experiments, I quantified behavior and selectivity of different sizes of these two fish feeding on lake zooplankton. Feeding behavior depended on fish size. Fish < 30 mm were visual feeders. Fish 30–50 mm either visually fed or pump-filter fed depending on zooplankton size. Fish > 70 mm were pump-filter feeders. Replicate 1 h feeding trials revealed that, as the relative proportions of prey changed during an experiment, acará (30–42 mm, standard length) and tilapia (29–42 mm) shifted from visual feeding on large evasive copepods to filter feeding on small cladocerans and rotifers. Electivity and feeding rate increased with prey length, but were distinct for similar-sized cladocerans and copepods. Visual/filter-feeding fish had lowest electivities for small and poorly evasive rotifers and cyclopoid nauplii. They fed non-selectively on cyclopoid copepodites, had intermediate electivities for calanoid nauplii and small cladocerans, and had highest electivities for large cladocerans, cyclopoid adults, and calanoid copepodites and adults. Although belonging to different cichlid genera and native to South America and Africa, respectively, acará and red-breasted bream (= congo tilapia) exhibited similar selectivity for zooplankton. Apparently, few stereotyped feeding behaviors have evolved during the acquisition of microphagy in fish. Shift in feeding modes allows these two species to optimally exploit the variable and dynamic patchy distribution of planktonic resources.     

Fluctuations in water level and the dynamics of zooplankton: a data‐driven modelling approach

1. The zooplankton in Lake Kinneret (Israel) have undergone large fluctuations in recent decades, which have been linked to both biotic and abiotic processes. 2. By applying a data‐driven modelling approach to a long‐term database, and focusing on key abiotic (lake‐level change) and biotic (prey abundance) variables, we attempted to identify the possible factors impacting the lake’s zooplankton community. 3. We hypothesised that changes in the predatory zooplankton (adult cyclopoids) assemblage are driven by changes in lake level during years of large changes. We further postulated that lake‐level changes would have a similar impact on the herbivorous zooplankton (cladocerans and cyclopoid copepodites) but an opposite effect on the microzooplankton. In the years of moderate changes to lake level, however, the abundance of predatory zooplankton would determine the size of the herbivore and microzooplankton populations rather than their food sources, that is, top‐down control. 4. The resulting decision trees supported the hypotheses stressing the importance of the annual rate of lake‐level change in shaping the zooplankton community in the lake. In addition, and in contrast to expectations, bottom‐up processes seem to play a role in determining zooplankton abundance.     

Generation time of Acanthocyclops robustus in relation to food availability and temperature in a shallow eutrophic lake

The generation time of the predatory cyclopoid copepod Acanthocyclops robustus was estimated on 11 occasions during the years 1980 to 1982 in Alderfen Broad. In a multiple regression model, generation time was found to be uncorrelated with temperature, positively correlated (p < 0.05) with the densities of Bosmina longirostris and rotifers, and negatively correlated (p < 0.001) with the density of nauplii of the calanoid copepod Eudiaptomus gracilis. It is suggested that generation time was determined largely by the availability of calanoid nauplii as prey, even though these constituted only 2% of zooplankton standing biomass.     

Temperature and prey density jointly influence trophic and non‐trophic interactions in multiple predator communities

相似文献   

Different Predation Impacts of Two Cyclopoid Species on a Small-sized Zooplankton Community: An Experimental Analysis with Mesocosms

We used mesocosms to analyze predation impacts on the prey populations and prey community structures by two cyclopoid copepod species, the larger Mesocyclops pehpeiensis and the smaller Thermocyclops taihokuensis, who coexist with small-sized herbivorous zooplankton species in a fish-abundant lake. The overall predation impact on the prey populations was stronger for Mesocyclops than for Thermocyclops. Mesocyclops had a strong and less selective impact on the rotifer community but a selective impact on the crustaceans. In contrast, Thermocyclops had a selective predation impact on rotifers but a weak and less selective impact on the crustacean community. As a result, the former predator reduced the diversity of the crustacean community but not the rotifer community, while the latter had an opposite impact on the diversities of the two communities. It has been suggested that fish induce development of a zooplankton community dominated by the small-sized zooplankton species in fish-abundant lakes. Our results demonstrated that cyclopoid copepods altered species composition and diversity of the small-sized zooplankton community in such lakes. Thus, the results have given an important suggestion on the role of the invertebrate predator cyclopoid copepods, which often coexist with fish, that they determine population dynamics and community structures of small-sized zooplankton in fish-abundant lakes.     

Calanoid–cyclopoid interactions: evidence from an 11-year field study in a eutrophic lake

1. The interactions between calanoid and cyclopoid copepods were examined in an 11-year field study of a eutrophic lake (Heiligensee, Berlin, Germany).
2. A diminishing ratio of calanoids to cyclopoids was observed. The responses, however, were species specific. While two cyclopoid species responded with increased populations ( Cyclops vicinus, Thermocyclops oithonoides ), one species exhibited marked declines ( C. kolensis ). Other species extended the duration of their pelagic phase ( Mesocyclops leuckarti, Diacyclops bicuspidatus, T. oithonoides, C. vicinus ), leading to higher population overlaps. Eudiaptomus graciloides and E. gracilis, which used to be present throughout the year, were more frequently absent.
3. These changes coincided with a series of mild winters during which prey availability (algae and rotifers) was high.
4. Enhanced prey availability, in conjunction with a flexible diapausing strategy, are hypothesized to underly the increased success of C. vicinus . Predatory losses due to early occurrence and enhanced abundances of C. vicinus, rather than competition for the same food resources, are hypothesized to be responsible for the declines of C. kolensis and Eudiaptomus .
5. Summer species tended to develop higher abundances early in the season, which led to enhanced seasonal means during spring. These changes cannot be explained by the interaction between calanoids and cyclopoids alone, but were probably a result of changes in fish predation.     

Effect of temperature extremes on the spatial dynamics of predator–prey interactions: A case study with dragonfly nymphs and newt larvae

Theory predicts that predators are more vulnerable to increasing temperature than prey. Despite huge variations in the magnitude and duration of thermally-extreme episodes in nature, most empirical studies on predator–prey interactions consider conditions induced by a climatic shift in mean temperature. We asked whether the increased vulnerability of predators holds under daily thermal extremes occurring during heat waves, using dragonfly nymphs and newt larvae as the predator–prey model system. Direct exposure of predator to prey in heated and non-heated aquaria under semi-natural conditions revealed that predator movements increased with rising temperature, whereas prey activity decreased. In contrast to the theory of predator–prey space use, the spatial co-occurrence of predator and prey individuals increased with temperature, while predation rates diminished. We conclude that daily thermal extremes affect trophic interactions in the same way, i.e. through the increased vulnerability of predators, as do long-term shifts in mean environmental temperature. Our results highlight the importance of behavioral studies for understanding mechanisms mediating the effect of extreme thermal events on species interactions.     

Cyanobacterial chemical warfare affects zooplankton community composition

1. Toxic algal blooms widely affect our use of water resources both with respect to drinking water and recreation. However, it is not only humans, but also organisms living in freshwater and marine ecosystems that may be affected by algal toxins. 2. In order to assess if cyanobacterial toxins affect the composition of natural zooplankton communities, we quantified the temporal fluctuations in microcystin concentration and zooplankton community composition in six lakes. 3. Microcystin concentrations generally showed a bimodal pattern with peaks in early summer and in autumn, and total zooplankton biomass was negatively correlated with microcystin concentrations. Separating the zooplankton assemblages into finer taxonomic groups revealed that high microcystin concentrations were negatively correlated with Daphnia and calanoid copepods, but positively correlated with small, relatively inefficient phytoplankton feeders, such as cyclopoid copepods, Bosmina and rotifers. 4. In a complementary, mechanistic laboratory experiment using the natural phytoplankton communities from the six lakes, we showed that changes in in situ levels of microcystin were coupled with reduced adult size and diminished juvenile biomass in Daphnia. 5. We argue that in eutrophic lakes, large unselective herbivores, such as Daphnia, are ‘sandwiched’ between high fish predation and toxic food (cyanobacteria). In combination, these two mechanisms may explain why the zooplankton community in eutrophic lakes generally comprise small forms (e.g. rotifers and Bosmina) and selective raptorial feeders, such as cyclopoid copepods, whereas large, unselective herbivores, such as Daphnia, are rare. Hence, this cyanobacterial chemical warfare against herbivores may add to our knowledge on population and community dynamics among zooplankton in eutrophic systems.     

Diel periodicity and selectivity in the feeding rate of the predatory copepod Mesocyclops edax

The diel periodicity and selectivity in the feeding behaviorof the predatory cyclopoid copepod Mesocyclops edax was investigatedat 3 h intervals over two 24 h sampling periods in nature. Gutcontent analyses revealed an increase in gut fullness at 11.30and 20.30 in July, and at 20.30 in August. The increase in gutfullness at these times could not be explained by an increasein prey density, changes in predator-prey overlap or differencesin prey vulnerability. We suggest that M.edax exhibits a truediel periodicity in the intensity of its predatory activities,although the alternative hypothesis of a diel periodicity ingut passage time cannot be ruled out. Vanderploeg and Scavia'sE^* selectivity index indicated a preference for rotifer andcladoceran prey over copepods.     

An experimental study of the effects of nutrient supply and Chaoborus predation on zooplankton communities of a shallow tropical reservoir (Lake Brobo, Côte d'Ivoire)

1. Based on two mesocosm experiments and 10 in vitro predation experiments, this work aimed to evaluate the impact of nutrient supply and Chaoborus predation on the structure of the zooplankton community in a small reservoir in Côte d'Ivoire. 2. During the first mesocosm experiment (M1), P enrichment had no effect on phytoplankton biomass (chlorophyll a) but significantly increased the biomass of some herbivorous zooplankton species (Filinia sp, Ceriodaphnia affinis). During the second experiment (M2), N and P enrichment greatly increased phytoplankton biomass, rotifers and cladocerans (C. affinis, C. cornuta, Moina micrura and Diaphanosoma excisum). In both experiments, nutrient addition had a negative impact on cyclopoid copepods. 3. Larger zooplankton, such as cladocerans or copepodites and adults of Thermocyclops sp., were significantly reduced in enclosures with Chaoborus in both mesocosm experiments, whereas there was no significant reduction of rotifers and copepod nauplii. This selective predation by Chaoborus shaped the zooplankton community and modified its size structure. In addition, a significant Chaoborus effect on chlorophyll a was shown in both experiments. 4. The preference of Chaoborus for larger prey was confirmed in the predation experiments. Cladocerans D. excisum and M. micrura were the most selected prey. Rotifer abundance was not significantly reduced in any of the 10 experiments performed. 5. In conclusion, both bottom‐up and top‐down factors may exert a structuring control on the zooplankton community. Nutrients favoured more strictly herbivorous taxa and disadvantaged the cyclopoid copepods. Chaoborus predation had a strong direct negative impact on larger crustaceans, favoured small herbivores (rotifer, nauplii) and seemed to cascade down to phytoplankton.     

Diurnal variation around an optimum and near‐critically high temperature does not alter the performance of an ectothermic aquatic grazer

The growing threat of global climate change has led to a profusion of studies examining the effects of warming on biota. Despite the potential importance of natural variability such as diurnal temperature fluctuations, most experimental studies on warming are conducted under stable temperatures. Here, we investigated whether the responses of an aquatic invertebrate grazer (Lymnaea stagnalis) to an increased average temperature differ when the thermal regime is either constant or fluctuates diurnally. Using thermal response curves for several life‐history and immune defense traits, we first identified the optimum and near‐critically high temperatures that Lymnaea potentially experience during summer heat waves. We then exposed individuals that originated from three different populations to these two temperatures under constant or fluctuating thermal conditions. After 7 days, we assessed growth, reproduction, and two immune parameters (phenoloxidase‐like activity and antibacterial activity of hemolymph) from each individual. Exposure to the near‐critically high temperature led to increased growth rates and decreased antibacterial activity of hemolymph compared to the optimum temperature, whilst temperature fluctuations had no effect on these traits. The results indicate that the temperature level per se, rather than the variability in temperature was the main driver altering trait responses in our study species. Forecasting responses in temperature‐related responses remains challenging, due to system‐specific properties that can include intraspecific variation. However, our study indicates that experiments examining the effects of warming using constant temperatures can give similar predictions as studies with fluctuating thermal dynamics, and may thus be useful indicators of responses in nature.     

Increased autumn rainfall disrupts predator–prey interactions in fragmented boreal forests

There is a pressing need to understand how changing climate interacts with land‐use change to affect predator–prey interactions in fragmented landscapes. This is particularly true in boreal ecosystems facing fast climate change and intensification in forestry practices. Here, we investigated the relative influence of autumn climate and habitat quality on the food‐storing behaviour of a generalist predator, the pygmy owl, using a unique data set of 15 850 prey items recorded in western Finland over 12 years. Our results highlighted strong effects of autumn climate (number of days with rainfall and with temperature <0 °C) on food‐store composition. Increasing frequency of days with precipitation in autumn triggered a decrease in (i) total prey biomass stored, (ii) the number of bank voles (main prey) stored, and (iii) the scaled mass index of pygmy owls. Increasing proportions of old spruce forests strengthened the functional response of owls to variations in vole abundance and were more prone to switch from main prey to alternative prey (passerine birds) depending on local climate conditions. High‐quality habitat may allow pygmy owls to buffer negative effects of inclement weather and cyclic variation in vole abundance. Additionally, our results evidenced sex‐specific trends in body condition, as the scaled mass index of smaller males increased while the scaled mass index of larger females decreased over the study period, probably due to sex‐specific foraging strategies and energy requirements. Long‐term temporal stability in local vole abundance refutes the hypothesis of climate‐driven change in vole abundance and suggests that rainier autumns could reduce the vulnerability of small mammals to predation by pygmy owls. As small rodents are key prey species for many predators in northern ecosystems, our findings raise concern about the impact of global change on boreal food webs through changes in main prey vulnerability.