Prey features affecting ingestion rates by Acanthocyclops robustus (Copepoda: Cyclopoida) on zooplankton

Summary (1) Ingestion rates by adult female and juvenile Acanthocyclops robustus on a number of prey types were measured at a prey concentration of 100/l in experimental volumes of 300–400 ml. (2) For the adult predator, Synchaeta pectinata was most vulnerable (22.3, standard error 1.4, prey ingested per predator per day) as compared to Brachiomus calyciflorus, Brachionus diversicornis, Keratella cochlearis (two morphs), Asplanchna priodonta, Polyarthra major, Synchaeta kitina, Pompholyx sulcata, Daphnia spec., and Bosmina longirostris. For these latter prey, the lowest ingestion rate was on one morph of K. cochlearis and the highest on A. priodonta, being, respectively, 1.0, SE 0.5, and 11.3, SE 1.0, prey per predator per day. (3) With regard to the juvenile predator (mostly copepodite stages I, II and III), ingestion rates on K. cochlearis and P. sulcata were low (respectively 1.2, SE 0.7, and 0.3, SE 0.1, prey per predator per day) but quite high on S. kitina (5.7, SE 0.6). (4) In addition, the effect of increasing prey concentration on the ingestion rate (functional response) by the adult female predator was examined for B. calyciflorus, K. cochlearis, S. pectinata, S. kitina and Daphnia spec.. Increases in ingestion rate with prey density were minimal for B. calyciflorus and K. cochlearis, greater for Daphnia spec., still greater for S. pectinata and of greatest magnitude for S. kitina. (5) The reasons for these results are discussed with particular reference to prey features.     

Spatial overlap of a predatory copepod,Acanthocyclops robustus,and its prey in a shallow eutrophic lake

Spatial overlap between Acanthocyclops robustus, with special emphasis on the adult females, and other zooplankton in one basin of a shallow (approximate depth of 2 m) eutrophic lake was studied.Horizontal distribution patterns were analysed on two dates. On both dates, most taxa examined showed large-scale patchiness between the three sections of the lake basin (approximate length of 1.2 km). Similarly, most taxa, with the important exception of the adult female Acanthocyclops robustus, were significantly patchily distributed on the small-scale (i.e. within sections). However, the intensity of such patchiness was, in general, relatively low. There was no consistent evidence of aggregation by the adult females or copepodites and adult males (the latter two were considered together) of the predator in such small-scale prey patches.Diurnal vertical distribution patterns were studied on two 24–25 hour periods. The first period was characterized by calm weather. Adult female, and perhaps male, Acanthocyclops robustus, Chydorus sphaericus, Bosmina Coregoni, Keratella cochlearis, Asplanchna species, Polyarthra vulgaris and Pompholyx sulcata seemed to show diurnal migration patterns, while seven other taxa showed consistent preferences for particular depths. Only copepod nauplii and Daphnia species were approximately evenly distributed. Negative correlations were found between the vertical distributions of the adult female predator and seven of the seventeen potential prey recognized.The first half of the second period was characterised by strong winds which abated during the second half. Most zooplankton taxa showed inconsistent heterogeneous vertical distributions or were homogeneously distributed with vertical heterogeneity developing towards the end of the period. Only Bosmina longirostris and Daphnia species seemed to show vertical migration patterns. Thus, no consistent vertical segregation between predator and prey was detected.     

Rotifers as indicators of lake types in Estonia

Data on the pelagic rotifer fauna in 10 Estonian lakes accumulated for 20 years, as well as published data are analysed. It is possible to distinguish three main indicator groups among rotifers: (1) for oligo- and mesotrophic lakes (Ploesoma hudsoni, Keratella serrulata, Synchaeta grandis, Asplanchna herricki, Ascomorpha ovalis, Gastropus stylifer, Conochilus hippocrepsis); (2) for meso-and eutrophic lakes (Trichocerca capucina, Filinia longiseta, F. limnetica, Keratella quadrata, K. cochlearis tecta, K.c. hispida, Polyarthra euryptera, Keratella hiemalis, Trichocerca porcellus, T. pusilla); (3) for eutrophic lakes (Brachionus spp., Anuraeopsis fissa, Pompholyx sulcata, P. complanata, Trichocerca cylindrica, Hexarthra mira).     

Seasonal development of planktonic rotifers in Slapy Reservoir (Czech Republic)

The rotifer community of the canyon shaped Slapy Reservoir was studied over four years, from 2000 to 2003. A total of 38 rotifer taxa were identified in the pelagial zone. The dominant species, Keratella cochlearis, K. quadrata, Polyarthra dolichoptera, P. vulgaris, Synchaeta lakowitziana and Pompholyx sulcata, were similar to other reservoirs in the same area. Tychoplanktic species, which are typical for communities of upstream reservoirs, are reduced in the Slapy Reservoir. The seasonal fluctuation of rotifer abundance is characterized by a significant spring peak, clear water depression, summer peak and sometimes a lower peak in autumn. Fluctuation of the rotifer species shows a highly unified trend through the years with very low variation through the years. It results from the input of hypolimnetic water from an upstream reservoir, which erased a large part of the effect of year to year climatic fluctuations.     

A comparative study of the functional response of four species of carnivorous stoneflies

SUMMARY 1. Comparisons were made of the functional responses of mature larvae of Perlodes microcephalus, Isoperla grammatica, Dinocras cephalotes and Perla bipunctata. Experiments were performed in stream tanks with natural substrata and glass bottoms, so that feeding could be observed above and below the substratum. There was one stonefly per tank and one of 10 prey densities between 20 and 200 larvae of either Chironomus sp. or Baetis rhodani per tank. Consumed prey were replaced in a first set of experiments but not in a second set. Additional experiments assessed intraspecific interference between larvae of each predator species (two to five predators per tank). 2. The number of prey eaten increased curvilinearly with prey density. The relationship was described by two models, a Type II instantaneous model and its integrated equivalent, for experiments with and without prey replacement, respectively. Handling time did not change significantly with prey density, and was the same for experiments with and without prey replacement. Estimates of attack rate were similar for the two models, but varied between prey type and predator species. Handling time varied considerably but was normally distributed for each prey type and predator species. Mean handling time varied for Chironomus from 39 s for Isoperla, which rarely ate a whole larva, to 57 s for Perlodes and for Baetis from 116 s for Perlodes to 167 s for Perla. All predators were more efficient at capturing Baetis, but the longer handling time for Baetis ensured that more Chironomus were eaten. It was concluded that these variations in attack rate and handling time were related to activity and growth differences between the predator species, and that experiments with and without prey replacement could both be relevant to the field, depending on how the predators searched for food. 3. In the interference experiments, mean handling time did not change with increasing predator density, but attack rate decreased curvilinearly, the decrease varying from negligible for Isoperla to marked for Perlodes. Prey capture decreased with decreasing attack rate. Therefore, interference reduced prey consumption, but this effect was negligible for Isoperla and increasingly severe in the order Dinocras, Perla and Perlodes.     

Post-encounter vulnerability of some rotifer prey types to predation by the copepod Acanthocyclops robustus

Prey characteristics affecting vulnerability of a number of rotifer species to the predator Acanthocyclops robustus were investigated. Body volume was the main feature affecting the probability of attack after encounter and, with the exception of Polyarthra major, capture after attack. The lorica provided protection against predation in some species and a skipping escape response reduced the likelihood of capture in Polyarthra major.     

Prey selectivity of Piona exigua,a planktonic water mite

Summary Females, males and nymphs of Piona exigua were observed during prey capture and ingestion. The encounter radius of the mite was very small, allowing the escape of some crustaceans, such as the calanoid copepod Boeckella. Cladocerans, such as Bosmina or Chydorus, with little or no pre-contact escape response were the most vulnerable to mite predation. Preference values in size-selection experiments varied widely between individual mites. Adult mites presented with two sizes of Daphnia carinata generally preferred the smaller prey. When four sizes were presented simultaneously, however, the preferences of female mites for each size were not significantly different. Patterns of prey selection varied with predator age and sex; for example, female mites preferred Daphnia to Simocephalus, Ceriodaphnia and Chydorus, while nymphs showed a strong preference for Chydorus over Ceriodaphnia. When two prey types were present in equal proportions, differences in total prey density (range 5 or 10/1 – 30 or 50/1) did not alter preferences between the prey species. The preference of female mites for a particular prey type generally increased with increasing relative abundance of the prey type in each of three experiments (Daphnia: Ceriodaphnia, Ceriodaphnia: Chydorus, and Daphnia: Simocephalus). These results imply switching behaviour in these mites. Our results indicate the value of direct observation of predatory behaviour as an adjunct to prey selection experiments. It is also apparent that predatory behaviour in the presence of more than one prey type may not be predictable from that observed in single-prey situations. Predation rates on particular prey species were sometimes reduced in the presence of another species. The relative proportions of prey eaten when two species were present could not be predicted from the number of each species eaten when they were presented separately.     

Culturing freshwater, planktonic rotifers on Rhodomonas minuta var. nannoplanctica Skuja and Stichococcus bacillaris Nageli

Eleven freshwater, planktonic rotifer species (Brachionus angularis,Brachionus cafyciflorus, Keratella quadrata, Nolholca squamula,Ascomorpha ecattdis, Synchaeta kitina, Synchaela tremula, Potyarthradolichoptera, Polyanhra vulgarii, Pompholyx sulcata, Filiniabrachiata) were cultured successfully on either Rhodomonas minutavar. nannoplanctica Skuja or Stichococcus bacillaris Nägeli,in a totally synthetic medium. Three of these species had notpreviously been kept in laboratory culture. The method is proposedas a simple technique for the routine batch culture of a varietyof planktonic rotifer species. Some important observations onhandling techniques, incubation temperature, culture vesselsand media are discussed.     

The ecology of Synchaeta kitina Rousselet in Loch Leven,Scotland

Synchaeta kitina Rousselet reached population densities of up to 5000 ind.l^–1 in Loch Leven, between January 1977 and December 1982. The species was found over the entire range of temperatures recorded (0.4–21.4 °C), but was most abundant at temperatures above 7 °C. Embryo development times, determined under laboratory conditions, ranged from 122 h at 2 °C to 12.5 h at 20 °C. There was a marked inverse relationship between populations of S. kitina and Daphnia hyalina var. lacustris in the loch. It seems unlikely that this was due to interference competition from Daphnia. S. kitina can be cultured on Rhodomonas minuta var. lacustris and there is some evidence that this rotifer also feeds on small flagellates in its natural environment.     

Oviposition patterns in a predatory mite reduce the risk of egg predation caused by prey

Abstract 1. Predatory arthropods lay their eggs such that their offspring have sufficient prey at their disposal and run a low risk of being eaten by conspecific and heterospecific predators, but what happens if the prey attacks eggs of the predator? 2. The egg distribution and time allocation of adult female predatory mites Iphiseius degenerans as affected by predation of their eggs by prey, the western flower thrips Frankliniella occidentalis, were studied on sweet pepper plants. The predatory mites attack the first instar of thrips but all active stages of thrips are capable of killing the eggs of the predator; however the predatory mite is used for biological control of thrips. 3. The majority of predatory mite eggs was laid on the underside of leaves in hair tufts (domatia). During the experiment, females spent increasing amounts of time in flowers where they fed on pollen and thrips larvae. The risk of predation on predator eggs by thrips was lower on leaves than in flowers where the majority of thrips resides. Moreover, predation risk was higher outside leaf domatia than inside. 4. This suggests that predators avoid ovipositing in places with abundant prey to prevent their eggs from being eaten by thrips.     

Ontogenetic shifts in the functional response and interference interactions of Rhyacophila dorsalis larvae (Trichoptera)

1. Ontogenetic shifts in predator behaviour can affect the assessment of food‐web structure and the development of predator–prey models. Therefore, it is important to establish if the functional response and interference interactions differ between life‐stages. These hypotheses were tested by (i) comparing the functional response of second, third, fourth and fifth larval instars of Rhyacophila dorsalis, using three stream tanks with one Rhyacophila larva per tank and one of 10 prey densities between 20 and 200 larvae of Chironomus sp.; (ii) using other experiments to assess interference within instars (two to five larvae of the same instar per tank), and between pairs of different instars (one, two or three larvae per instar; total predator densities of two, four or six larvae per tank). 2. The first hypothesis was supported. The number of prey eaten by each instar increased with prey density, the relationship being described by a type II model. The curvilinear response was stronger for fourth and fifth instars than for second and third instars. Mean handling time did not change significantly with prey density, and increased with decreasing instar number from 169 s for fifth instars to 200 s for second instars. Attack rate decreased progressively with decreasing instar number. Handling time varied considerably for each predator–prey encounter, but was normally distributed for each predator instar. Variations in attack rate and handling time were related to differences in activity between instars, fourth and fifth instars being more active and aggressive than second and third instars, and having a higher food intake. 3. The second hypothesis was partially supported. In the interference experiments between larvae of the same instar or different instars, mean handling time did not change significantly with increasing predator density, and attack rate did not change for second and third instars but decreased curvilinearly for fourth and fifth instars. Interference between some instars could not be studied because insufficient second instars were available at the same time as fourth and fifth instars, and most third instars were eaten by fourth and fifth instars in the experiments. Prey capture always decreased with decreasing attack rate. Therefore, interference reduced prey consumption in fourth and fifth instars, but not in second and third instars. The varying feeding responses of different instars should be taken into account when assessing their role in predator–prey relationships in the field.     

Feeding responses of Asplanchna brightwelli (rotifera): laboratory and field studies

Laboratory-reared A. brightwelli were offered 16 different prey rotifer species from the genera Anuraeopsis, Brachionus, Epiphanes, Filinia, Hexarthra, Lecane, Lepadella, Pompholyx, Proalides and Trichocerca. Feeding responses (prey encounter, escape, capture, rejection and ingestion) were recorded. In general, the predator's ingestion time was positively correlated with prey length. B. falcatus and H. intermedia were never captured. Once captured, smaller rotifer species were ingested. Gut contents of field-collected A. brightwelli revealed increased occurrence of prey numbers when concentrated plankton samples were preserved after some delay.     

Study of the Trophi of <Emphasis Type="Italic">Testudinella</Emphasis> Bory de St. Vincent and <Emphasis Type="Italic">Pompholyx</Emphasis> Gosse (Rotifera: Testudinellidae) by Scanning Electron Microscopy

The fine morphology of the trophi of Pompholyx sulcata and nine species of Testudinella (Rotifera, Monogononta, Flosculariacea, Testudinellidae) was studied by scanning electron microscopy. The number of unci teeth and arched rami scleropili, and the shape of the major unci teeth and fulcrum are considered to be reliable additional characters for identification.     

Handling time, prey preference, and functional response for Chrysoperla rufilabris in the laboratory

The predaceous larvae of Chrysoperla rufilabris (Burmeister) exhibited some success-motivated searching, particularly when feeding on Heliothis virescens (F.) eggs, but handling time did not decrease with experience. Handling time for H. virescens larvae was more than twice that for eggs. H. virescens larvae were preferred to cotton aphids (Aphis gossypii (F.)) while aphids were preferred to H. virescens eggs. C. rufilabris larvae exhibited a linear functional response to the three prey types tested, over the prey densities tested.USDA, ARS, Retire. Present address: 200 Highland, College Station, TX 77840, USA     

Feeding rate and attack specialization: the roles of predator experience and energetic tradeoffs

Synopsis Individual mosquitofish, Gambusia affinis, can adopt a broad range of attack selectivities. In part, this variation can be explained by the past experiences of a fish. Individuals selected the more profitable Ceriodaphnia dubia (Cladocera) over less profitable cyclopoid copepods to a greater degree after being exposed to both prey types than did individuals experienced with only one of the prey types. Feeding rate (biomass ingested per unit time) declined with increased attack specialization on the profitable prey (Ceriodaphnia) when such prey were scarce, a result in agreement with assumptions of optimal diet theory. When profitable prey were abundant feeding rate was a bimodal function of the intensity of specialization on profitable prey; fish that specialized on cyclopoid copepods (the less profitable prey type) fed at higher rates than did generalists. This may be the result of antagonistic learning that precluded feeding efficiently on more than one type of prey at a time. The data are consistent with the hypothesis that rejection of unsuitable prey involves a time cost. The two preceeding aspects of foraging behavior, which are absent from most optimal diet models, could lead to failure in predicting the attack specialization of some predators, An additional aspect of the results was the generally weak relationship between feeding efficiency and specialization behavior. This suggests that feeding rate may not have been as tightly linked to the specialization behavior a predator adopts as is assumed by current foraging theory.     

Effect of beetle size on predation of cabbage root fly eggs by ground beetles

Laboratory studies were done to determine the numbers of cabbage root fly (Delia radicum L.) (Diptera: Anthomyiidae) eggs eaten by sixty species of ground beetles (Coleoptera: Carabidae) collected from a range of habitats. For 35 species that were between 2.7 mm and 10 mm long, there was a linear relationship between the numbers of eggs eaten and beetle length. For each 1 mm increase in length above 2.7 mm, an additional 18 eggs were eaten/beetle/day. Eight further species within the above size range did not eat any fly eggs, as these species are known to be either phytophagous or to feed on moving prey. Large numbers of eggs were eaten by beetles in 13 of the 25 genera tested. Based on size, maximum numbers of eggs were eaten by 7 species of Agonum Bonelli, 5 species of Amara Bonelli and seven species of Bembidion Latreille. Only one of the 6 species of Pterostichus Bonelli tested, P. strenuus (Panz.), ate the expected numbers of eggs, the other species being too large to feed from such small prey items as cabbage root fly eggs. The numbers of beetles larger than 10 mm that ate eggs was highly variable and so 10 mm was considered the upper size limit of carabid predators of cabbage root fly eggs.     

Notes taxinomiques sur quelques Rotifères planctoniques

Résumé Les caractères spécifiques des différentes espèces appartenant aux genres Keratella, Polyarthra, Synchaeta, Filinia, Conochiloides, Conochilus sont discutés en fonction des observations effectuées par l'auteur dans les collections d'eau de la région parisienne.

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Summary The specific characters of the different species from the genus Keratella, Polyarthra, Synchaeta, Filinia, Conochiloides, Conochilus are discussed according to the observations made by the author in the water collections of the parisian region.

     

Functional response of the predator <Emphasis Type="Italic">Scolothrips takahashii</Emphasis> to hawthorn spider mite, <Emphasis Type="Italic">Tetranychus viennensis</Emphasis>: effect of age and temperature

A leaf disc bioassay was employed to examine the effects of temperature and predator age on functional response of an acarophagous thrips, Scolothrips takahashii Priesner, to hawthorn spider mite, Tetranychus viennensis Zacher, in the laboratory. The results indicated that the predatory thrips exhibited type-II functional responses against the mites under various temperatures, and that females are more voracious than males. Analysis showed that temperature had significant effects on the predatory capacity of adult thrips over the range of 20–35 °C. Attack rate in females linearly increased with temperature while in males it was independent of temperature. Handling times in both males and females decreased linearly with increasing temperature. Extended response models describing the functional response with temperature incorporated as a parameter were developed, yielding an estimated maximum numbers of prey attacked at four temperatures were 38.38, 55.06, 71.74 and 88.42 eggs per day for females, and 15.11, 26.11, 37.11 and 48.01 eggs per day for males, respectively. The age of predator affected both the type of the functional response shown and the magnitude of predation by S.␣takahashii on the spider mite. Females of various ages exhibited Type-II functional responses with similar attack rates, but handling time prolonged linearly as age increased: the handling times in 15- and 18-d-old females were significantly longer than in 6-d-old thrips. However, Type-I functional responses were determined for males aged 12 d or more; the maximum number of prey eaten in 24 h decreased as age increased. The implications of the results for the management of hawthorn spider mite are discussed.     

Selective feeding of Arctodiaptomus salinus (Copepoda, Calanoida) on co-occurring sibling rotifer species

1. Using two‐ and three‐dimensional video recordings, we examined the steps involved in predation that lead to the differential vulnerability of three sympatric rotifer sibling species (Brachionus plicatilis, B. ibericus and B. rotundiformis) to a co‐occurring, predatory, calanoid copepod (Arctodiaptomus salinus). 2. Brachionus rotundiformis, the smallest prey tested, was the most vulnerable with the highest encounter rate, probability of attack, capture and ingestion, and the lowest handling time. 3. Comparison of our results with those of a previous study shows that A. salinus is a more efficient predator than a co‐occurring cyclopoid copepod (Diacyclops bicuspidatus odessanus) feeding on these same rotifer species. However, despite its higher capture rates, A. salinus seems to be less selective than D. b. odessanus based on attack distances and prey handling times. 4. The differential vulnerability to both calanoid and cyclopoid copepod predation can help explain the coexistence and seasonal succession of these co‐occurring rotifer species.     

The essential omega-3 fatty acid EPA affects expression of genes involved in the metabolism of omega-6-derived eicosanoids in Daphnia magna

We quantified the predation of Acanthocyclops americanus from the shallow Mediterranean lake Albufera, using gut contents from field collections and laboratory feeding tests. For functional response studies, we used Brachionus plicatilis (at 6 concentrations, 400–4000 ind. 40 ml⁻¹) and Diaphanosoma mongolianum (at 2–20 ind. 40 ml⁻¹). Copepod feeding rates were also estimated using different proportions of rotifer prey and lake seston (0–67.5% of seston + 40 individuals of B. plicatilis). Prey selection studies were conducted using five zooplankton species: Brachionus angularis, Brachionus plicatilis, Keratella tropica, Daphnia magna and Diaphanosoma mongolianum. Gut contents of field-collected adult Acanthocyclops contained filamentous algae and cyanobacteria and 16 zooplankton species (Keratella cochlearis, unspined and spined forms, K. tropica, Brachionus plicatilis, Brachionus calyciflorus, Brachionus angularis, Brachionus variabilis, Asplanchna girodi, Polyarthra vulgaris, Synchaeta pectinata, Lepadella rhomboides, unidentified bdelloids, Alona rectangula, Chydorus sphaericus, Bosmina longirostris, D. magna, Ceriodaphnia dubia and copepod nauplii). When fed B. plicatilis or D. mongolianum, female A. americanus had higher prey consumption rates than males. Increased proportion of lake seston caused reduced consumption of brachionid prey. Our data suggest that A. americanus is omnivorous in nature.