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.     

Experimental analysis of the predation impact of the larvae of pond smelt (<Emphasis Type="Italic">Hypomesus transpacificus nipponensis</Emphasis>) on zooplankton populations established in mesocosms

The predation impact of the larvae of pond smelt Hypomesus transpacificus nipponensis on a zooplankton community was studied using mesocosms. The fish significantly depressed the abundances of copepod nauplii and rotifers, especially Hexarthra mira. The vulnerabilities of these prey might be determined by their swimming behavior and population density, suggesting that larval fish selectively prey on zooplankton that have a high encounter rate with the predator. The larvae did not have a negative effect on the densities of cladocerans, but fish predation altered the cladoceran community structure from the dominance of B. longirostris to that of B. fatalis. This result suggests that larval fish predation is an important factor that shifts the species composition of Bosmina in some lakes, the shift occurring in the season when fish larvae are abundant. Our results have shown that predation by the larval fish would control not only the abundance, but also the community structure of the small-sized zooplankton prey.     

Effect of the cyclopoid copepod Mesocyclops thermocyclopoides on the interactions between the predatory rotifer Asplanchna intermedia and its prey Brachionus calyciflorus and B. angularis

In many shallow, eutrophic subtropical ponds, brachionid rotifers are common prey of the predatory copepod Mesocyclops thermocyclopoides. The predatory rotifer Asplanchna intermedia, which is itself a potential prey of the copepod, also feeds preferentially on brachionids. We studied in the laboratory the population dynamics of two mutually competing prey species, Brachionus angularis and B. calyciflorus, in the presence of the two predators A. intermedia and M. thermocyclopoides. The experimental design included separate population dynamics studies with one prey–one predator, two prey–one predator, one prey–two predator, and two prey–two predator systems. These combinations were compared with controls, in which both the prey species (B. angularis and B. calyciflorus) were grown separately and in combination with each other. In the absence of any predator, B. angularis generally eliminated the larger B. calyciflorus. Selective predation by the copepod allowed B. calyciflorus to persist longer in competition with B. angularis. Feeding by M. thermocyclopoides on A. intermedia reduced the predation pressure on B. calyciflorus. However, given enough time, the cyclopoid copepod was able to eliminate both the brachionids as well as the predatory Asplanchna.     

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.

     

Food of an endangered cyprinodont (Aphanius iberus): ontogenetic diet shift and prey electivity

Synopsis We studied the ontogenetic diet shift and prey electivity of an endangered cyprinodontid fish endemic to the Iberian Peninsula, the Spanish toothcarp (Aphanius iberus). The toothcarp’s diet was omnivorous, dominated by harpacticoid copepods (Mesochra lilljeborgi and Tisbe longicornis), copepod nauplii and detritus. Diet composition varied greatly among habitats, depending on prey availability. In a rarely inundated habitat (glasswort), there was more consumption of the isopod Protracheoniscus occidentalis and the harpacticoid copepod Mesochra lilljeborgi, while in algal mats another harpacticoid (Tisbe longicornis), chironomid dipterans and invertebrate eggs were more important in diet. Although a benthic feeding habitat has previously been suggested, in our study the diet was based rather on water column organisms for both glasswort and algal mat habitats. There was also an ontogenetic diet shift, with an increase of mean prey length with fish length, clearly linked to a microhabitat change. Smaller fish showed positive electivity and greater reliance on planktonic prey (e.g. copepod nauplii, the harpacticoid copepods Mesochra lilljeborgi and Tisbe longicornis, the rotifer Brachionus plicatilis, and ostracods), while larger fish elected and preyed on more benthic organisms (e.g. Canuella perplexa, Mesochra rapiens, and ephydrid dipterans).     

Prey handling time and ingestion probability for Mesocyclops sp. predation on small cladoceran species Bosmina longirostris, Bosminopsis deitersi, and Scapholeberis mucronata

We compared the vulnerability of small cladoceran species (Bosminopsis deitersi, Bosmina longirostris, and Scapholeberis mucronata) to predation by Mesocyclops sp. in the laboratory based on prey handling time and ingestion probability. We also estimated the effects of ontogenetic changes on handling time by testing prey of various body sizes. All tested prey species showed an increasing pattern of handling time along with growth (increase of body size). For juveniles smaller than 0.3mm, the prey handling time was similar for B. deitersi and B. longirostris, but markedly longer for S. mucronata. Mesocyclops sp. rejected large (>0.35mm) B. longirostris and S. mucronata soon after capture and consequently showed a low probability of successful ingestion, whereas most large individuals of B. deitersi were consumed. The shorter handling time and higher ingestion probability of small juveniles indicate that the copepods ingest small juveniles more efficiently than larger individuals. Thus, it seems that the vulnerability of small cladocerans to copepod predation differs ontogenetically, with the greatest vulnerability being during the juvenile period. The ontogenetic reduction in the vulnerability of B. longirostris and S. mucronata was shown in the rapidly reduced ingestion probability as well as by the increase in prey handling time for large individuals. The results show that the vulnerability to predation by copepods of B. longirostris and S. mucronata reduces more quickly with increasing size than does that of B. deitersi, and it seems that the former two species are more resistant to copepod predation.     

Some aspects of vulnerability to cyclopoid predation of zooplankton prey individuals

The predation cycle (encounter, attack, capture and ingestion or survival) by adult female Acanthocyclops robustus was observed for four crustacean prey types. The chief defense of A. robustus nauplii was escape response ability, reducing the probability of capture after attack, and, most likely, attack after encounter. The most important feature reducing the vulnerability of Ceriodaphnia and Daphnia species was large body size, decreasing the probability of capture after attack. Escape response ability and carapace strength/integrity further reduced vulnerability. Carapace strength/integrity was an effective defense for Bosmina longirostris, reducing the probability of ingestion after capture.The predation cycle by juvenile A. robustus was examined for three prey types. All three prey types seemed to be readily attacked. Due to their possession of loricae, Keratella cochlearis and Pompholyx sulcata were seldom eaten, while the illoricate Synchaeta kitina was highly vulnerable.Egg vulnerability after attack by the adult female predator was analysed. The eggs of Brachionus calyciflorus, Pompholyx sulcata and Filinia longiseta were rarely eaten, although the adults of the latter were usually ingested (thus causing the eggs to float free). Out of three attacks recorded on Keratella Quadrata, the eggs were eaten (or destroyed) twice.Handling times by the adult female predator were measured for a number of prey types. The shortest mean handling time was for Synchaeta kitina (less than one second), while the longest was on Ceriodaphnia species (716 seconds). Results were quite variable. Handling time was significantly positively related to prey body volume, while exoskeletal strength/integrity also increased this time. No effect of temperature on handling time was found for Synchaeta pectinata or Polyarthra major between 15 and 26.5 °C.     

Sacrificial males: the potential role of copulation and predation in contributing to copepod sex‐skewed ratios

Predation is thought to play a selective role in the emergence of behavioural traits in prey. Differences in behaviour between prey demographics may, therefore, be driven by predation with select components of the population being less vulnerable to predators. While under controlled conditions prey demography has been shown to have consequences for predation success, investigations linking these implications to natural prey population demographics are scarce. Here we assess predator–prey dynamics between notonectid predators (backswimmers) and Lovenula raynerae (Copepoda), key faunal groups in temperate ephemeral pond ecosystems. Using a combination of field and experimental approaches we test for the development and mechanism of predation‐induced sex‐skewed ratios. A natural population of L. raynerae was tracked over time in relation to their predator (notonectid) and prey (Cladocera) numbers. In the laboratory, L. raynerae sex ratios were also assessed over time but in the absence of predation pressure. Predation success and prey performance experiments evaluating differences between L. raynerae male, female, gravid female and copulating pairs exposed to notonectid predation were then examined. Under natural conditions, a female dominated copepod population developed over time and was correlated to predation pressure, while under predator‐free conditions non sex‐skewed prey population demographics persisted. Predator–prey laboratory trials showed no difference in vulnerability and escape performance for male, female and gravid female copepods, but pairs in copula were significantly more vulnerable to predation. This vulnerability was not shared by both sexes, with only female copepods ultimately escaping from successful predation on a mating pair. These results suggest that contact periods during copula may contribute to the development of sex‐skewed copepod ratios over time in ecosystems dominated by hexapod predators. This is discussed within the context of vertebrate and invertebrate predation and how these dissimilar types of predation are likely to have acted as selective pressures for copepod mating systems.     

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.     

Antennule shape and body size of <Emphasis Type="Italic">Bosmina</Emphasis>: key factors determining its vulnerability to predacious Copepoda

Cyclopoid copepods are common in lakes and ponds, and they have a significant predation impact on the communities of the small zooplankton species. To reduce the predation risk, some cladoceran zooplankters develop protuberant (defensive) morphologies in the presence of the copepods. In the case of the small cladoceran Bosmina, they elongate their appendages (antennule and mucrone) and change the antennule morphotype. However, information about the effectiveness of these defensive devices against copepod predation is still insufficient. In our study, to find the compositive effects of these appendages on the vulnerability of Bosmina, we exposed two bosminid species (B. longirostris and B. fatalis) of different body sizes and with appendages of different lengths and shapes to copepod (Mesocyclops) predation. The experiment revealed that the shape of the antennule is a main factor determining the bosminid’s vulnerability to copepod predation and indicated that the protection of the opened ventral carapace must be a key strategy by which Bosmina avoids copepod predation.     

Spatial Partitioning of Predation Risk in a Multiple Predator-Multiple Prey System

ABSTRACT Minimizing risk of predation from multiple predators can be difficult, particularly when the risk effects of one predator species may influence vulnerability to a second predator species. We decomposed spatial risk of predation in a 2-predator, 2-prey system into relative risk of encounter and, given an encounter, conditional relative risk of being killed. Then, we generated spatially explicit functions of total risk of predation for each prey species (elk [Cervus elaphus] and mule deer [Odocoileus hemionus]) by combining risks of encounter and kill. For both mule deer and elk, topographic and vegetation type effects, along with resource selection by their primary predator (cougars [Puma concolor] and wolves [Canis lupus], respectively), strongly influenced risk of encounter. Following an encounter, topographic and vegetation type effects altered the risk of predation for both ungulates. For mule deer, risk of direct predation was largely a function of cougar resource selection. However, for elk, risk of direct predation was not only a function of wolf occurrence, but also of habitat attributes that increased elk vulnerability to predation following an encounter. Our analysis of stage-based (i.e., encounter and kill) predation indicates that the risk effect of elk shifting to structurally complex habitat may ameliorate risk of direct predation by wolves but exacerbate risk of direct predation by cougars. Information on spatiotemporal patterns of predation will be become increasingly important as state agencies in the western United States face pressure to integrate predator and prey management.     

Predator-prey interactions and community structure: chironomids,mosquitoes and copepods in Heliconia imbricata (Musaceae)

Summary Evidence from both field observations and experimental work indicates that predation by larvae of a midge, Pentaneura n. sp. (Chironomidae), causes the low densities of mosquito larvae (Culicidae) found in the water filled bracts of Heliconia imbricata (Musaceae), microhabitats typically colonized by mosquitoes. This predation affects 2 species of mosquitoes, Wyeomyia pseudopecten, a resident species, and Trichoprosopon digitatum, a non-resident species. Predation keeps resident mosquito densities low while completely excluding the nonresident mosquito from the habitat. Both these effects of predation depend on the presence of an abundant alternative prey, an undescribed species of harpacticoid copepod found in the bracts. These copepod prey sustain chironomids when resident mosquito densities are low, permiting predator densities to remain high enough to exclude the non-resident mosquito. I discuss the evolutionary and ecological implications of predation structuring communities.     

The feeding behaviour of Leptodora kindti and its impact on the zooplankton community of Neusiedler See (Austria)

Leptodora kindti is a very efficient invertebrate predator. Its searching mode of preying is tactile. The setae of the first thoracic limb act as mechanoreceptors, the other thoracic limbs, thorax and head together form the shape of an open basket in which after encounter the prey is pushed in by the aid of the first thoracic limbs and the furca. In Neusiedler See, small individuals of Diaphanosoma brachyurum (0.6–0.9 mm) are the preferred prey, rarely copepods are taken. The predation rate is influenced by temperature, prey density and predator size and varies between less than one and 12 prey items per predator per day. At high predator densities, Leptodora will have a substantial effect on the Diaphanosoma population of Neusiedler See.     

Diel vertical migration of the copepod <Emphasis Type="Italic">Thermocyclops inversus</Emphasis> (Kiefer, 1936) in a tropical reservoir: the role of oxygen and the spatial overlap with <Emphasis Type="Italic">Chaoborus</Emphasis>

The effect of water transparency, dissolved oxygen concentration and the invertebrate predator Chaoborus brasiliensis on the day–night vertical distribution of the copepod cyclopoid Thermocyclops inversus was investigated in a shallow tropical reservoir, Nado Reservoir, Belo Horizonte, Brazil. Diel cycles were carried out over a period of 12 consecutive months, between October 1999 and September 2000. The different developmental stages of T. inversus exhibited diel vertical migration (DVM) and displayed a clear ontogenetic trend, with the amplitude of DVM increasing with the age of the organism, and ranging from 0.4 m to 0.8 m for nauplii, 0.4 m to 1.2 m for copepodite, and 1.1 m to 2.1 m for adults. We observed that seasonal changes in dissolved oxygen and C. brasiliensis directly influenced the vertical distribution of the copepod population in this reservoir. Furthermore, it was showed that the diurnal vertical migration is an important predator avoidance behavior since it diminished the spatial overlap between prey and its potential predator. This finding supports the hypothesis that the vertical migration is a defense mechanism against predation. Thus, T. inversus is able to remain in the anoxic layers during day light hours, and at night they move upwards avoiding hypolimnetic waters to escape from predation by Chaoborus.     

Additive multiple predator effects can reduce mosquito populations

1. Multiple predator interactions may profoundly alter ecological community dynamics and can complicate predictions of simpler pairwise predator–prey interaction strengths. In particular, multiple predator effects may lessen or enhance prey risk, with implications for community-level stability. Such emergent effects may modulate natural enemy efficacy towards target organisms. 2. In the present study, a functional response approach was used to quantify emergent multiple predator effects among natural enemies towards the disease vector mosquito complex, Culex pipiens. Conspecific multiple predator–predator interactions of the cyclopoid copepod Macrocyclops albidus (intermediate predator) were quantified by comparing multiple predator consumption simulations, based on individual consumption rates, with multiple predator consumption rates that were experimentally observed. Further, the study examined the influence of the presence of a predator at a higher trophic level, Chaoborus flavicans, on copepod group predation. 3. Both predators displayed type II functional responses, with C. flavicans consuming significantly more prey than M. albidus individually. Overall consumption levels of mosquitoes increased with greater predator density and richness. Antagonistic or synergistic emergent multiple predator effects between conspecifics of M. albidus were not detected, and the higher-level predator did not reduce effects of the intermediate predator. Accordingly, evidence for additive multiple predator interactions was found. 4. The lack of predator–predator interference between cyclopoid copepods and larval chaoborid midges provides strong support for their combined application in mosquito biocontrol. It is proposed that there should be increased examination of multiple predator effects in assessments of natural enemy efficacies to better understand overall predatory effects within communities and utilities in vector control.     

The influence of prey behaviour on prey selection of the carnivorous plant Utricularia vulgaris

The mechanisms underlying differential prey selection of two microcrustaceans by the common bladderwort (Utricularia vulgaris) were studied in the laboratory. Functional response experiments with single prey showed that Utricularia had a higher attack rate coefficient and a longer handling time coefficient with the cladoceran Polyphemus pediculus than with the cyclopoid copepod Eucyclops serrulatus. Observation of predation rate, defined as number of prey eaten per unit time, from direct behavioural observation on single prey species, showed a higher predation rate with Polyphemus than on Eucyclops, at low prey densities. The opposite pattern was found at high prey density. When the two prey were presented simultaneously to the predator, Eucyclops was preferred over Polyphemus. Results from the situation with two prey and some of the results from the direct behavioural observations support field data on the diet of Utricularia, which shows that cyclopoid copepods are selected more frequently than Polyphemus.     

Patterns of prey selectivity in the cyclopoid copepod Mesocyclops thermocyclopoides

In the shallow and eutrophic subtropical aquatic ecosystems, which it generally inhabits, the omnivorous copepod Mesocyclops thermocyclopoides encounters a wide variety of animal prey types including ciliates, rotifers, and cladocerans. We studied prey selectivity in laboratory-reared adult females of this species given a choice of (i) prey types belonging to different taxa (ciliates, rotifers, cladocerans, and cyclopoid nauplii), and (ii) different prey species within a taxonomic group differing in body size, morphology or behaviour. We also tested the effect of different proportions of prey species on its selectivity. Prey type proportion had no significant effect on selectivity of the copepod, nor was there any evidence of switching based on the relative abundance of prey. Among the ciliate prey species tested, the largest species, Stylonychia mytilus was positively selected regardless of its relative abundance, while the smallest, S. notophora was selected only when its density was higher. Offered a choice of three species of a brachionid rotifer differing in size, the copepod selected the largest of them, Brachionus calyciflorus, and avoided the smallest B. angularis. The evasive rotifer Hexarthra mira was also avoided. When prey choice included three cladoceran species Daphnia similoides, Moina macrocopa and Ceriodaphnia cornuta, the copepod selected the intermediate-sized M. macrocopa regardless of the abundance of the other two species. Although it fed on Mesocyclops nauplii when there was no choice, M. thermocyclopoides avoided them when alternative food was available. In a multispecies prey choice test, the copepod selected predominantly the rotifer B. calyciflorus and the cladoceran M. macrocopa. We suggest that the prey selectivity patterns shown by M. thermocyclopoides are adaptive in that they lead to ingestion of the most profitable prey.     

The possibility of predator avoidance by Lake Michigan zooplankton

Low densities of Diaptomus ashlandi, Diacyclops thomasi, and Daphnia galeata mendotae were measured at depths where Mysis relicta formed nighttime aggregations. Calculations suggest that mysid predation can not account for the rarity of prey animals at these depths, which further suggests that the prey avoided the mysids. Unlike D. galeata mendotae, Daphnia pulicaria was common in mysid aggregations. The somewhat larger size of D. pulicaria may reduce its vulnerability to mysid predation, and consequently may explain the vertical distribution differences between the two congeners. Vertical distributions of Limnocalanus macrurus and copepod nauplii showed no obvious relationships to the mysid distributions. These were the only two taxa with distributions that were correlated with chlorophyll a concentrations. All crustacean taxa were rare in the epilimnion at night when sonar recorded a dense fish school.     

Influence of cyanobacterial diet on Asplanchna predation risk in Brachionus calyciflorus

Asplanchna sylvestrii does not discriminate between groups of Brachionus calyciflorus fed either the cyanobacterium Anabaena flos-aquae or a control diet of Euglena gracilis. We based our analysis on the observed probabilities of attack, capture and ingestion during encounters between predator and prey. While A. sylvestrii was very sensitive to brachionid size, we found no significant affects of prey diet on predatory behavior. Thus, cyanobacterial diet did not influence the short-term predation risk of B. calyciflorus exposed to an effective predator. On the other hand, matched cohorts of A. sylvestrii fed B. calyciflorus cultured on the cyanobacterium reproduced more slowly than those fed the same prey cultured on the control food. With prolonged sympatry, therefore, the long-term risk of Asplanchna predation may be reduced for Brachionus by the latter's consumption of cyanobacteria.     

A method for in situ estimation of prey selectivity and predation rate in large plankton, exemplified with the jellyfish Aurelia aurita (L.)

A method to estimate predation rates of large predatory zooplankton, such as jellyfish and ctenophores, is outlined. Large plankton size allows direct visual tracking of the predator during the process of foraging. The presented method is novel in the sense that it measures predation rate of a specific individual plankton predator in situ.After prey has been evacuated from the gut of an individual predator, the predator is incubated in situ, and observed by SCUBA-divers who recapture the individual after a defined time. Given that this incubation time is shorter than prey digestion time, predation rate can be calculated as increase in gut content over time. Clearance rates for different prey can be calculated from predation rates and prey concentrations in the water, allowing accurate estimates of prey selectivity. Thus, the problem of unknown feeding history and feeding environment, which can otherwise be a problem in prey selectivity studies of in situ-captured predators, is circumvented. Benefits and limitations of the method are discussed.The method was applied to adult medusae of the common jellyfish Aurelia aurita. A large variation in number of captured prey was detected both among individual jellyfish and among the various oral arms and gastric pouches within individuals. Clearance rates varied strongly with prey type. The medusae selected large crustacean prey (cladocerans and copepods/copepodites) over echinoderm larvae and copepod nauplii. Prey distribution within the medusae indicates that both tentacles and oral arms were used as prey capturing sites. Food passage time from prey capturing organs to gastric pouches was estimated.