Large Daphnia Research Articles

Phenotypic plasticity of Daphnia pulex in the presence of invertebrate predators: morphological and life history responses.

Morphological and life history traits of two clones of the cladoceran Daphnia pulex were measured in the presence and absence of size-selective insect predators, the midge larva Chaoborus flavicans, which preys on small Daphnia, and the water bug Notonecta glauca, which preys on large Daphnia. The aim was to detect predator-induced phenotypic changes, particularly the effect of simultaneous exposure to both types of predators. Other work has shown that in the presence of Chaoborus americanus, Daphnia pulex produce a socalled neck spine which may carry several teeth. The morphological modifications are supposed to serve as an anti-predator device. Furthermore, females exposed to Chaoborus often delay their maturation; this has been interpreted as a cost that balances the benefits of the neck teeth. In this investigation, females of both clones produced fewer but larger offspring than control animals when reared in the presence of Chaoborus flavicans. The offspring showed the typical neck spine and delayed first reproduction. In the presence of Notonecta glauca, one of the clones produced more and smaller offspring, and maturation occurred at earlier instars. The other clone also produced more offspring than the control but there was no size difference. When both predators were present, in most cases the reactions of the daphnids were similar to those in the Notonecta experiment. The response to Chaoborus appeared to be suppressed. The observed modifications are interpreted as evolved strategies that reduce the impact of size-selective predation. They are consistent with predictions of life-history theory.

Differential zooplankton feeding behaviors, selectivities, and community impacts of two planktivorous fishes

We examined the feeding behaviors and selectives of two common planktivorous fishes, pumpkinseeds Lepomis gibbosa and fathead minnows Pimephales promelas in the laboratory. Ingestion rates for both pumpkinseeds and fathead minnows feeding on zooplankton increased as a function of fish length. Pumpkinseeds fed on zooplankton strictly as particulate feeders, with preferences increasing as a function of zooplankton body size regardless of taxonomic identity. Preferences were highest for large Daphnia, intermediate for intermediate-sized copepods, and lowest for small Ceriodaphnia. Fathead minnows displayed the ability to use both particulate-feeding and filter-feeding behaviors. Differential preferences tended to reflect both zooplankton size and taxon, being highest for large, slow-swimming Daphnia, intermediate for small Ceriodaphnia, and lowest for faster-swimming copepods. These differences in prey capture behaviors and preferences of the two fishes are reflected in the zooplankton taxonomic composition of small ponds containing each fish type. The crustacean zooplankton assemblages in ponds containing both pumpkinseeds and fathead minnows were dominated by copepods. Cladocerans were rare. In ponds containing pumpkinseeds, but no fathead minnows, cladocerans were abundant, generally accounting for up to 80% of total crustacean zooplankton biomass. These results suggest that the type of planktivore, and not simply the presence or abundance of planktivores in a system, can determine zooplankton community structure.

Density-dependent predation ofChaoborus flavicans onDaphnia longispina in a small lake: the effect of prey size

Functional response curves of fourth instar larvae ofChaoborus flavicans preying on two size classes ofDaphnia longispina were examined throughout three summer seasons in a small forest lake. Data for each size class were fitted to Holling's disc equation. The parametersa′ (attack rate) andTh (handling time) were calculated for each prey size from these curves. Attack rate was greater and handling time was shorter for small (0.77 mm) than for large (1.82 mm)Daphnia. In 1:1 mixture of these prey size classes the predation rates ofChaoborus on smallDaphnia at prey densities above 20 l−1 were greater than predicted from the single size-class experiments. The observed predation rates on largeDaphnia were lower than predicted at all prey densities. Since both single size-class and two size-class experiments were run during the same period of time the difference in observed and predicted predation rates could not be attributed to seasonal changes in prey preference ofChaoborus larvae. In experiments with a concentrated mixture of lake zooplankton (dominated byD. longispina)Chaoborus preference forDaphnia decreased as prey body size increased. There was no obvious correlation between selectivity coefficients and size-frequency distributions ofDaphnia. When medium-sizedDaphnia were omitted from calculations the preference of small over large prey did not differ significantly from the predictions of the single size-class model.

Trophic Level Relationships in Pelagic Food Webs: Comparisons Derived from Long-Term Data Sets for Oneida Lake, New York (USA), and Lake St. George, Ontario (Canada)

We used standardized methods to analyze a 14-yr data set from Oneida Lake and a 10-yr data set from Lake St. George. We estimated mean summer concentrations of several trophic level indicators including piscivores, planktivores, zooplankton, phytoplankton, and total phosphorus, and we then investigated the relationships between these variables. Both data sets yielded similar long-term and short-term trends. The long-term mean annual trends were that (1) the relationships between concentrations of planktivores and zooplankton (including daphnids) were always negative, (2) the relationships between concentrations of zooplankton and various measures of phytoplankton abundance were unpredictable and never statistically significant, and (3) the relationships between total phosphorus and various measures of phytoplankton abundance were always positive. Over short periods, the data from both lakes showed periodic, strong top-down relationships between concentrations of zooplankton (especially large Daphnia) and chlorophyll a, but these events were unpredictable and were seldom related to piscivore abundance.

Growth‐Related Constraints on Diet Selection by Sunfish

Diet selectivity by the planktivorous bluegill sunfish (Lepomis macrochirus) is correlated with the fishes' visual resolution. Poor visual capabilities are thought to impose a constraint on the ability of small sunfish to chose prey. Li et al. (1985) suggested that sunfish subjected to conditions of poor visual resolution select prey in accordance with a model in which prey choice is determined by apparent prey size. Further, enhanced visual resolution permitted large sunfish to assess absolute prey size more accurately than could smaller conspecifics and, consequently, large—sized sunfish consumed relatively more large prey than was predicted by the apparent size model. Here, we examine the visual capabilities and prey selection of very small sunfish, extend the analyses of Li et al. by determining the optimal diet sets for the fish used in their study, and compare prey selection by all sunfish size categories to that predicted by the apparent size and optimal foraging models. Contrary to the conclusions of Li et al., small sunfish (<20 mm standard length [SL]) were more selective than was predicted by the apparent size model and preferentially attacked small—sized Daphnia. The optimal foraging "prey" model predicted correctly the size—related changes in mean size of prey attacked by sunfish, whereas the apparent size model predicted a preference for large Daphnia for all sizes of fish. Yet, the observed diet breadths were always larger than those predicted by the optimal foraging model. The visual system any energy considerations constrain prey selection in small sunfish but operate in opposite fashions.

Predation Risk and the Importance of Cover for Juvenile Rainbow Trout in Lentic Systems

Abstract Juvenile rainbow trout Oncorhynchus mykiss stocked in midelevation reservoirs in Utah inhabit shallow nearshore areas and are vulnerable to predation from piscivorous fish and birds. We determined the use and importance of nearshore habitats by (1) measuring habitat selection by, prey availability to, and feeding of juvenile rainbow trout in two reservoirs with populations of predators, and (2) measuring survival and growth rates in the presence and absence of cover in a pond experiment where adult brown trout Salmo trutta were predators. In the reservoirs juvenile rainbow trout (60–120 mm standard length) were abundant in complex inshore habitats but avoided simple habitats such as sand and gravel during the day. At night, however, juvenile rainbow trout in both reservoirs were observed in more exposed areas, and they rested on the bottom. Measurements of gut fullness indicated that juvenile rainbow trout fed actively on large Daphnia spp. during the day but little at night. Because large daphni...

Regulation of Planktonic Microbial Communities by Nutrients and Herbivores

We conducted a series of single—factor and factorial experiments in two north—temperate lakes (Peter and Paul lakes, Gogebic County, Michigan, USA) to study regulation of heterotrophic microbial communities. In single—factor experiments large Daphnia were added to enclosures, and these were compared to enclosures without Daphnia. These treatments contrast the major food—web configurations that occur in these lakes as a consequence of cascading trophic interactions. Bacterial abundance and the incorporation of methyl [3H]—thymidine into DNA by bacteria were similar in treatments with and without Daphnia. Ciliates were significantly reduced while heterotrophic flagellates were only marginally reduced by Daphnia additions in the Peter Lake experiments. Protozoans were not affected by Daphnia additions in the Paul Lake experiment. Factorial experiments compared the relative significance of large daphnids and nutrients as regulators of bacteria and protozoa. Treatments included controls, Daphnia additions, nutrient (N plus P) additions, and a combined Daphnia—nutrient treatment. Bacteria responded to nutrient additions but not to Daphnia. Protozoa, on the other hand, were strongly affected by Daphnia and to a lesser extent by nutrients. These experiments suggest that the trophic cascades is truncated at the level of protozoans. Protozoa appear to be partially regulated by predators, whereas bacteria show no response to changes in either Daphnia or protozoa.

Size-specific swimming behavior of Daphnia pulex

Body length affects several aspects of the behavior of quietly swimming Daphnia pulex Swimming and sinking rates were measured at 0.033 s intervals during the 'hops' characteristic of Daphnia swimming behavior Larger animals swim faster, cover more distance, and produce more powerful swimming strokes. Larger Daphnia also sink faster, but the sinking rate scales as length to the 0 58 power, far lower than the power of 2 00 predicted by Stokes Law considerations. The number of hops s1 was independent of body size, although a theoretical analysis predicts hopping rate (antennal beat frequency) should increase as body length squared. Turning behavior, measured as the ratio of displacement to total distance, during 5 s, is also independent of body size Independence of several parameters of body motion and body size implies that factors other than simple mechanics affect Daphnia swimming behavior

Effects of planktivorous fish mass mortality on the plankton community of Lake Mendota, Wisconsin: implications for biomanipulation

Massive mortality of planktivorous fish had a dramatic impact on plankton community dynamics of Lake Mendota, Wisconsin, USA. After fish mortality, the larger Daphnia pulicaria replaced the smaller Daphnia galeata mendotae, resulting in greater grazing pressure on phytoplankton. This was accompanied by a much longer spring clear-water period and lower summer phytoplankton biomass compared to years before the fish mortality. Analysis of historical data (from the mid-1970’s) showed that previous fluctuations in planktivorous abundance had similar effects on Daphnia abundance and species composition, and on spring phytoplankton biomass. However, the mid-1970’s fish fluctuations had no detectable effect on summer phytoplankton. Concentrations of phosphorus were much higher in the 1970’s (spring P 80–135 μg 1−1 ’) than in the 1980’s (spring P 19–36 μg 1−1) and it is possible that high P concentrations may reduce trophic cascade effects on summer phytoplankton communities. This suggests that the success of biomanipulation programs may be dependent on lake nutrient status.

Trophic interactions of Leptodora in Lake Mendota

Using a series of field enclosure experiments, we investigated the trophic dynamics of Leptodora kindtii in Lake Mendota. Leptodora fed on both small and large Daphnia as well as on Diaphanosoma, Conochilus, and copepod nauplii. These results were combined with field data and a computer simulation model to examine how various densities of Leptodora might affect the densities of Daphnia and other zooplankton in Lake Mendota. Leptodora could account for all of the mortality calculated for Daphnia galeata mendotae in late June to early July. Reduced numbers minimized Leptodora’s potential, however, for direct control of Daphnia earlier in the year. The simulation model demonstrated that, because the dominant planktivorous fish in the lake fed on both Leptodora and daphnids, a decrease in planktivorous fish could result in higher Daphnia mortalities due to increased predation by Leptodora.

Direct assessment of the independent effects of exploitative and interference competition between Daphnia and rotifers

It is well established that large Daphnia can markedly reduce rotifer populations in both natural communities and laboratory cultures, but the mechanism for this reduction has been debated. Both exploitative competition for resources and interference have been invoked, but experiments have not directly assessed the independent roles of these mechanisms. Using laboratory chambers divided with 53-µm Nitex screen, I have separated the effects of interference from exploitative competition by Daphnia pulex on Keratella cochlearis and Keratella crassa. At both high and low food levels, K. cochlearis is strongly affected by interference competition but not exploitative competition, and K. crassa shows no evidence of suppression by Daphnia through interference competition. These results suggest that laboratory studies examining the effects of Daphnia on rotifers are correct in attributing much of the reduction in rotifer numbers to direct interference competition.

Influence of Prey Abundance on Species and Size Selection by Young Yellow Perch (Perca flavescens)

Prey selection by young yellow perch (Perca flavescens) (22–62 mm TL) was measured during 11 experiments over two summers, 1982–83. For each experiment fish were offered different densities of the same mixture of zooplankton from Oneida Lake, NY. As density of prey increased, several measures of selectivity for Daphnia either remained unchanged or declined, while all measures of selectivity for calanoids and cyclopoids increased. At all densities small to mid-sized Daphnia were preferred to large Daphnia. Reanalyses of other studies suggests this may be the general pattern for young planktivores, despite the contrary predictions of several models of prey selection. For young planktivores, differences in the nutritional quality of zooplankton prey, including resultant growth efficiency and speed of digestion, can account for these results.

Effects on lower trophic levels of massive fish mortality

PREDATION can be a potent force structuring ecological communities and affecting several trophic levels1–7. The cascading trophic interactions hypothesis predicts that lacustrine predators such as fish can have a strong effect on herbivorous zooplankton, which in turn can regulate phytoplankton8,9. Ascertaining the scale, scope and generality of this hypothesis is important for both development of ecological theory and aquatic ecosystem management10. Although small-scale tests of parts of this cascade are common11–15, whole-lake assessments are not, particularly in large, natural lakes9; also the influence of several trophic levels and nutrients, a requisite for unambiguous interpretation of predator effects, has not been considered. Here we present data from a natural experiment in Lake Mendota, Wisconsin, USA, which support the cascading trophic interactions hypothesis. Massive mortality of fish greatly reduced prEdation on zooplankton, resulting in an increase in the abundance of large Daphnia, and a dramatic decrease in phytoplankton biomass. Physical factors and concentrations of limiting nutrients were unchanged before and after fish mortality, indicating that these factors probably did not cause the observed decrease in phytoplankton. Our results demonstrate strong food web influences on phytoplankton, and support the idea that food web interactions can be managed to reduce phytoplankton abundance.

Perturbation Planktivory, and Pelagic Community Structure: The Consequence of Winterkill in a Small Lake

The top predator (largemouth bass, Micropterus salmoides) in eutrophic Wintergreen Lake, Michigan, was eliminated by successive winterkills in 1978 and 1979. Within 2 yr, the golden shiner (Notemigonus crysoleucas), a facultative planktivore, dominated the fish community. The zooplankton, previously consisting of large Daphnia pulex and D. galeata mendotae, concomitantly shifted to a community consisting of smaller species: Bosmina and small copepods. In situ fish enclosure experiments in 1981 and 1982 revealed that the large Daphnia species would grow in Wintergreen Lake in the absence of the golden shiner. Golden shiners exhibit both a particulate and filtering mode of planktivory on large and small zooplankton, respectively. This flexible feeding behavior suggests that golden shiners are able to prevent the reestablishment of Daphnia, while Bosmina and the other small zooplankton support a high and apparently stable golden shiner density.

The susceptiblity of Keratella cochlearis to interference from small cladocerans

SUMMARY. 1. Even at high population densities (300–2000 ind. 1−1), only one of five small cladoceran species (adult body length <1 mm) significantly suppressed population growth of the rotifer Keratella cochlearis through interference (encounter) competition. At 500 ind. H, adults of D. ambigua (0.96 mm body length) imposed an instantaneous per capita death rate of 0.21 day−1 on this rotifer. These short‐term experiments may have underestimated cladoceran interference because newborn rotifers were rarely present.2. Newborn rotifers (<12 h old) were much more susceptible than adult rotifers (> 24 h old) to interference from Ceriodaphnia dubia. All of the small cladoceran species tested were very much less likely than large Daphnia (body lengths >1.2 mm) to interfere with K. cochlearis, but perhaps at high population densities they could suppress population growth of susceptible rotifer species by damaging, and possibly eating, relatively small and soft‐bodied newborn individuals.3. K. cochlearis of the tecta form, without a posterior spine, produced offspring of the typica form, with a posterior spine, in the presence of C. dubia. This developmental response is stimulated by at least several, and possibly all, cladocerans and probably reduces the susceptibility of the rotifer to cladoceran interference.

Changes in Prey Rank and Preference by Young Planktivores for Short-Term and Long-Term Ingestion Periods

Feeding by young planktivorous fishes (yellow perch, Perca flavescens, rainbow trout, Oncorhynchus mykiss, and lake trout, Salvelinus namaycush) was examined. Prey rank was determined by offering a swarm of one prey type and observing ingestion rates. During the initial feeding burst, larger prey generally ranked higher. During long-term feeding the largest prey, large Daphnia magna, generally declined in rank while the smallest prey, Diaptomus sicilis, increased to the highest or second highest rank. Prey preference was measured with fishes feeding in a swarm of mixed prey. Initially small rainbow trout and yellow perch selected for large Daphnia then switched to Diaptomus. For small rainbow trout this switch in prey preference paralleled the change in prey rank. For yellow perch, large Daphnia and Diaptomus provided essentially the same long-term ingestion rates. The nearly exclusive selection for Diaptomus during long-term feeding did not agree with prey rank based on caloric ingestion rates. Previous work has shown that yellow perch have a high growth efficiency on a diet of Diaptomus. Selection for Diaptomus suggests that fish can rank prey by nutritional quality as well as caloric ingestion rates.

Suppression of rotifer populations by Daphnia: A review of the evidence, the mechanisms, and the effects on zooplankton community structure1

There is strong evidence that rotifers cannot become abundant members of freshwater zooplankton communities in the presence of large (≳ 1.2 mm) Daphnia. Indirect evidence comes from field observations and experiments showing that rotifers are replaced by Daphnia in seasonal successions, that rotifers are much less common in communities with than without Daphnia, and that the experimental addition of zooplanktivorous fish causes the removal of Daphnia and a simultaneous increase in rotifer abundance, while the experimental removal of fish has just the opposite effect. Direct evidence comes from field experiments showing that the removal of Daphnia from communities causes a marked increase in the fertility and abundance of rotifers, and from laboratory experiments showing that Daphnia can kill and rapidly exclude rotifers in mixed‐species cultures. Rotifers are suppressed by large Daphnia both through exploitative competition for shared, limiting food resources and through mechanical interference. This interference can cause high mortality rates on susceptible rotifer species, even at low (1–5 ind. liter‒1) Daphnia densities and should affect the species structure of rotifers able to coexist with Daphnia in natural communities.Rotifers seem to be much less inhibited by small 1.2 mm) cladocerans and often co‐occur with them at high densities in natural communities in the absence of large Daphnia. There are several reasons why small cladocerans are less likely than large Daphnia to competitively suppress rotifers: small cladocerans generally do not mechanically interfere with rotifers, are less likely to deplete food resources, are themselves more likely to be suppressed by exploitative competition with rotifers, and usually are more susceptible to invertebrate predation. High rotifer abundance in the absence of Daphnia competition may have an important secondary effect in natural communities—the development of populations of invertebrate predators dependent on rotifer prey.

Large Daphnia as an indicator of fish predation on another zooplankton species (Holopedium gibberum Zaddach)

Large <i>Daphnia</i> as an indicator of fish predation on another zooplankton species (<i>Holopedium gibberum</i> Zaddach)

The Population Dynamics of Daphnia At Constant Food Supply: a Review, Re-Evaluation and Analysis of Experimental Series From the Literature

Data on the population dynamics of five Daphnia species, viz. D. galeata mendotae, D. obtusa, D. pulicaria, D. pulex and D. magna, were collected from the literature. The experiments with constant food input were re-analysed for the oscillatory behaviour of the populations. Some populations appear to stabilize, whereas others continue to fluctuate. Some fluctuations are apparently caused by external factors. A decline to far below the average population size is always followed by a large population overshoot. Even populations that tend to stabilize do so by way of a series of damped oscillations. The oscillation period depends on, among other things, the Daphnia species, and increases with its size. Sometimes the same feeding regime leads to an equal or greater population size for a larger Daphnia species. This suggests that the chosen food species was not equally suitable for the two Daphnia species. No effect of crowding on the population size of Daphnia is found.

A Field Manipulation of Trophic Interactions in Rock-Pool Plankton

Three rock-pools (ca. 10 Daphnia 1-1, ca. 100 Daphnia 1and > 100 Daphnia 1-1) were each bisected with a plastic curtain. One side of each pool was left intact, while planktivorous fish were introduced into the other side. The succession of the zooplankton and phytoplankton communities in the rock-pools was followed, using quantitative sampling, for one summer. In the experiment the fish eliminated large (> 0.5 mm) herbivorous cladocers from the zooplankton within 20-40 d of introduction. An increase in the numbers of small zooplankton (rotifers, cladocers) then occurred. In the control sides large Daphnia thrived well, though with fluctuating densities, throughout the summer. The response of phytoplankton to the elimination of large herbivores varied between the rock-pools. In terms of species diversity and evenness no obvious differences were observed between control and experiment in the rock-pool with low Daphnia density. In the medium-density rock-pool both species diversity and evenness were lower in the experimental part, while in the high-density rock-pool the opposite was observed. In these two pools elimination of Daphnia resulted in an increase in total numbers of cells 11 of 2-3 orders of magnitude. The difference between control and experimental parts was due to the increase in small cells (< 64 Bm diameter). The elimination of large herbivores resulted in lowered densities (low-density) or elimination (medium and high-density) of filamentous algae from the phytoplankton.