Scaling the effects of predation and disturbance in a patchy environment

The effects of hydraulic disturbances on the impact of two predatory benthic invertebrates on their prey were examined in a stream at two distinct spatial scales. At the scale of small habitat patches (0.0625 m²), hydraulic patch type was an important determinant of the microdistribution of prey and predators. Prey abundances were similar across all patch types at baseflow, but local densities were higher in patches identified as low-flow refugia after periods of high and fluctuating flow. The microdistribution pattern of predatory larvae of a caddisfly, Plectrocnemia conspersa, was similar to that of its prey, whereas predatory larvae of an alderfly, Sialis fuliginosa, did not shift their microdistribution significantly with discharge and were always most abundant in lowflow refugia. There was little evidence of an aggregative response of predators with prey, even though both predators and prey are mobile. Both predator species showed similar patch-specific patterns of per capita consumption rates: uniform consumption rates across hydraulic patch types at low and moderate flows, but highest in flow refugia during high flows. Species-specific patterns, however, were apparent in the magnitude and direction of differences between consumption rates during disturbance events, and in comparable patches at base flow: At high flow, consumption rates for P. conspersa were exaggerated (3.9 times higher) in flow refugia but at par in other patches; for S. fuliginosa they were at par in flow refugia but reduced in other patches (up to 3.3. times lower). These differences may be related to species-specific foraging behaviours (search vs ambush predators) and the influence of prey movements on feeding success. Using the patch-scale results only, it is difficult to predict the effects of physical disturbance on predation intensity at the larger scales of whole habitats, populations or communities. At the large scale (>200 m²), net predator impacts were estimated over the stream reach, using a spatially explicit model that accounts, in an additive way, for habitat heterogeneity and patch-specific responses of predators and prey. The relationship between predator impact over the whole reach and hydraulic disturbance differed for the two predators. The predator impact of S. fuliginosa decreased with increasing hydraulic disturbance, as predicted by the harsh-benign hypothesis. There was no directional trend for P. conspersa, however, and maximum predator impact may occur at intermediate disturbance levels. For the prey community in this stream, predation pressure from S. fuliginosa appears to fluctuate directly with the discharge hydrograph, whereas predation from P. conspersa may be more persistent. Flow refugia may play a dual role in the sructure of stream communities by preventing catastrophic mortality of animals (predators and prey) from physical forces during disturbances, and by maintaining (or perhaps increasing) predation pressure. Summing the effects of species interactions in small habitat patches to the larger scale of a whole stream reach indicates that the scale of approach influences the observed patterns and their implied underlying process.     

Diet and predators of Tenagomysis tasmaniae Fenton, Anisomysis mixta australis (Zimmer) and Paramesopodopsis rufa Fenton from south-eastern Tasmania (Crustacea:Mysidacea)

The diets of three mysid species Tenagomysis tasmaniae Fenton, Anisomysis mixta australis (Zimmer) and Paramesopodopsis rufa Fenton were investigated together with a number of potential fish predators by gut contents and stable isotope analysis. Gut content analysis of the three mysis species revealed that all have an omnivorous diet, although the stomachs of P. rufa contained a greater percentage of crustacean remains, whereas the stomach contents of T. tasmaniae were largely composed of fragments of macroalgae. The stomach contents of A. mixta australis were composed mainly of fine particulate matter. Diel feeding rhythms were examined from mysids collected during a 24-hour sampling session in October. P. rufa appeared to be primarily a day-time feeder while T. tasmaniae fed more intensively at night. The results for A. mixta australis were inconclusive. Gut contents analysis of fish collected at the study site revealed predation on mysids by Arripis trutta (juveniles), Aldrichetta forsteri, Vincentia conspersa and Pseudolabrus fucicola. The mysid species most frequently eaten was Tenagomysis australis Fenton. The mysid species most frequently eaten was Tenagomysis australis Fenton.     

Molecular diagnostics reveal spiders that exploit prey vibrational signals used in sexual communication

Vibrational signalling is a widespread form of animal communication and, in the form of sexual communication, has been generally regarded as inherently short‐range and a private communication channel, free from eavesdropping by generalist predators. A combination of fieldwork and laboratory experiments was used to test the hypothesis that predators can intercept and exploit such signals. First, we developed and characterized PCR primers specific for leafhoppers of the genus Aphrodes and specifically for the species Aphrodes makarovi. Spiders were collected from sites where leafhoppers were present and screened with these primers to establish which spider species were significant predators of this species during the mating period of these leafhoppers. Analysis using PCR of the gut contents of tangle‐web spiders, Enoplognatha ovata (Theridiidae), showed that they consume leafhoppers in the field at a greater rate when signalling adults were present than when nymphs were dominant, suggesting that the spiders were using these vibrations signals to find their prey. Playback and microcosm experiments then showed that E. ovata can use the vibrational signals of male leafhoppers as a cue during foraging and, as a result, killed significantly more male than female A. makarovi. Our results show, for the first time, that arthropod predators can exploit prey vibrational communication to obtain information about prey availability and use this information to locate and capture prey. This may be a widespread mechanism for prey location, one that is likely to be a major unrecognized driver of evolution in both predators and prey.     

Trophic relationships: integrating meiofauna into a realistic benthic food web

• 1 This paper summarises the most important contributions on trophic relationships of lotic meiofauna. In contrast to marine research, the few quantitative studies of the freshwater meiobenthos have shown that these invertebrates not only take up particulate/fine organic matter, but also dissolved organic substances attached to organic particles. In lotic ecosystems, further estimates of grazing rate and bacterial/algal ingestion rate are needed, particularly in situ measurements.
• 2 The effects of macroinvertebrate predators upon meiofauna are still under debate. Depending on the type of experiments (laboratory vs. field) it seems that macrofauna may or may not affect meiofauna. Field samples and analyses of gut contents of larval tanypod chironomids have shown that the impact upon meiofauna was low and larvae were nonselective predators. Predation amounted to 2.2% of the combined prey density and prey consumption averaged 1.3 individuals per predator individual per year.
• 3 Adding taxonomic resolution by including the meiofaunal component within lotic food webs distinctly increases the number of total species and, as a consequence, changes food web statistics. Webs that included meiofauna revealed that these metazoans contributed substantially to the percentage of intermediate species (species with predators and prey). The resolution of dietary analyses of major consumers of macro‐ and meiobenthos showed that many stream invertebrates feed on meiofauna.

     

Diet and trophic position of two mackerel species in the archipelago of Madeira,Portugal

The Atlantic chub mackerel Scomber colias and the blue jack mackerel Trachurus picturatus are two abundant species in the Macaronesia region which includes the archipelago of Madeira, Portugal. Both are key species in the trophic web, being important prey for several local top predators, such as seabirds and marine mammals. Nonetheless, little is known about their feeding ecology in oceanic environments. In this study, the authors describe the seasonal variation in the diet of S. colias and T. picturatus in the oceanic region of Madeira throughout a year. Visual inspection of stomach contents revealed that S. colias fed on a broader range of prey groups than T. picturatus, but for both species, zooplankton (particularly calanoid copepods) and fish were the most important food items. The diet of S. colias included a higher proportion of fish, namely Atlantic saury Scomberesox saurus and S. colias, than that of T. picturatus, that included mostly the longspine snipefish Macroramphosus scolopax. T. picturatus consumed a higher proportion of decapods and other copepods. Seasonal variation was found in the diet of both species, with zooplanktonic species being more important in colder months (February to April) for S. colias and during warm months (May to October) for T. picturatus. Their diet in other seasons was dominated by fish. Although they consume similar prey, carbon and nitrogen stable isotope analysis of muscle of S. colias and T. picturatus showed little overlap in their diets, and T. picturatus showed higher δ¹⁵N and a narrower isotopic niche.     

Potential of Periplaneta fuliginosa densovirus as a biocontrol agent for smoky-brown cockroach, P. fuliginosa

A densovirus, named Periplaneta fuliginosa densovirus (PfDNV), affects smoky-brown cockroach (P. fuliginosa), which is a major peridomestic cockroach in China, southeastern United States, Japan, and Southeast Asia. We reported here that PfDNV could be mass-produced using virus rescue technology. Pathology and ultrastructural studies revealed the presence of enlarged and dense nuclei in hindgut cells of infected smoky-brown cockroach nymphs and adults. Laboratory bioassays of the PfDNV against P. fuliginosa showed that it has the potential to be used as a biocontrol agent. High mortality was recorded in adult smoky-brown cockroaches treated with PfDNV baits at the dosage of 6 × 10⁴ virions per gram against P. fuliginosa in both no-choice tests and two-choice tests (LT₅₀’s were 13.37 and 13.50 days, respectively). PfDNV was also effective in large population chamber tests. LT₅₀ was 17.57 days and mortality achieved was 95.6% in 28 observation days.     

Landscape, habitat characteristics and the genetic population structure of two caddisflies

1. In a region of south‐eastern England, we investigated the hierarchical genetic structure of populations of two stream‐dwelling caddisflies (Trichoptera: Polycentropodidae) with contrasting distributions: Plectrocnemia conspersa inhabits numerous small, patchily distributed seeps and streams, while the confamilial Polycentropus flavomaculatus is found in fewer but larger streams and rivers. We also contrasted the genetic structure of P. conspersa in the lowland south‐east with that in an upland region in the north west. 2. Microsatellite genotypes were obtained from samples of both species taken from a ‘core area’ and at sites 15, 40 and 100 km from this core (two regions for P. conspersa, totalling 45 sites and 1405 larvae; one region for P. flavomaculatus, totalling 10 sites and 269 larvae). 3. The genetic structure of P. conspersa differed in the two regions. In the upland north‐west, significant genetic differentiation was observed at a spatial scale of around 40 km from the core, while there was no structure in the lowland south‐east up to around 100 km. Areas of high altitude did not appear directly to reduce gene flow, whereas other potential landscape barriers, including particular geological formations, large urban areas and the sea had a pronounced effect. 4. Weak genetic differentiation in P. conspersa across large distances, particularly in the lowland south‐east, suggests that it disperses strongly, facilitating gene flow within and between catchments. Conversely, for P. flavomaculatus we found strong genetic differentiation between almost all sites, suggesting that dispersal is much more limited. 5. Greater dispersal in the patchily distributed P. conspersa than in P. flavomaculatus, which occupies larger and presumably more persistent habitats, could be a general feature of other similarly distributed aquatic insects. While higher relief is potentially a partial barrier to dispersal, P. conspersamust have effective gene flow through such apparently inhospitable terrain, perhaps attributable to dispersal between neighbouring small and ephemeral populations. Indeed, its exploitation of headwaters and seeps requires the ability to disperse between such sites. Apparently it cannot, however, overcome more continuous barriers, consisting of large tracts of landscape with few habitable larval sites. Such landscapes, including those created by humans, may have a stronger effect on population connectivity and colonization in the longer term.     

The role of notothenioid fish in the food web of the Ross Sea shelf waters: a review

The Ross Sea, a large, high-latitude (72–78°S) embayment of the Antarctic continental shelf, averages 500 m deep, with troughs to 1,200 m and the shelf break at 700 m. It is covered by pack ice for 9 months of the year. The fish fauna of about 80 species includes primarily 4 families and 53 species of the endemic perciform suborder Notothenioidei. This review focuses on the diet and role in the food web of notothenioids and top-level bird and mammal predators, and also includes new information on the diets of artedidraconids and bathydraconids. Although principally a benthic group, notothenioids have diversified to form an adaptive radiation that includes pelagic and semipelagic species. In the southern Ross Sea, notothenioids dominate the fish fauna at levels of abundance and biomass >90% and are, therefore, inordinately important in the food web. Antarctic krill (Euphausia superba) and mesopelagic fishes are virtually absent from the shelf waters of the Ross Sea. Of the four notothenioid families, nototheniids show the most ecological and dietary diversification, with pelagic, cryopelagic, epibenthic and benthic species. Neutrally buoyant Pleuragramma antarcticum constitutes >90% of both the abundance and biomass of the midwater fish fauna. Most benthic nototheniids are opportunistic and feed on seasonally or locally abundant zooplanktonic prey. Artedidraconids are benthic sit-and-wait predators. Larger bathydraconids are benthic predators on fish while smaller species feed mainly on benthic crustaceans. Channichthyids are less dependent on the bottom for food than other notothenioids. Some species combine benthic and pelagic life styles; others are predominantly pelagic and all consume euphausiids and/or fish. South polar skuas, Antarctic petrels, Adélie and emperor penguins, Weddell seals and minke and killer whales are the higher vertebrate components of the food web, and all prey on notothenioids to some extent. Based on the frequency of occurrence of prey items in the stomachs of fish, bird and mammal predators, P. antarcticum and ice krill E. crystallorophias are the key species in the food web of the Ross Sea. P. antarcticum is a component of the diet of at least 11 species of nototheniid, bathydraconid and channichthyid fish and, at frequencies of occurrence from 71 to 100%, is especially important for Dissostichus mawsoni, Gvozdarus svetovidovi and some channichthyids. At least 16 species of notothenioids serve as prey for bird and mammal predators, but P. antarcticum is the most important and is a major component of the diet of south polar skua, Adélie and emperor penguins and Weddell seals, at frequencies of occurrence from 26 to 100%. E. crystallorophias is consumed by some nototheniid and channichthyid fish and can be of importance in the diet of emperor and Adélie penguins, although in the latter case, this is dependent on location and time of year.Unlike the linear phytoplanktonE. superbaconsumers of the E. superba food chain hypothesized for much of the Southern Ocean, the food web of the Ross Sea shelf is non-linear, with complex prey-predator interactions. Notothenioid fish play a key role: as predators, they occupy most of the trophic niches available in the ecosystem, relying on benthic, zooplanktonic and nektonic organisms; as prey, they are important food resources for each other and for most top predators living and foraging on the shelf. They also constitute the major link between lower (invertebrates) and higher (birds and mammals) levels of the food web. This is especially true for P. antarcticum. Along with E. crystallorophias, its ecological role in the Ross Sea is equivalent to that of myctophids and E. superba elsewhere in the Southern Ocean.     

Diet of the small-spotted catshark Scyliorhinus canicula in the Aegean Sea (eastern Mediterranean)

The diet of the small-spotted catshark Scyliorhinus canicula, captured in the Aegean Sea by bottom-trawl from 2006 to 2012, was investigated with respect to sex, maturity condition, sampling location and season. The stomach contents of 432 specimens, measuring from 144 to 517?mm in total length, were analysed. The cumulative prey curve showed that the sample size was adequate to describe the species’ diet, which was quantified using the percentage gravimetric composition (%W). The identified prey items belonged to eight major groups: Teleostei, Chondrichthyes, Crustacea, Cephalopoda, Annelida, Echinodermata, phanerogams and macroalgae, with Teleostei, Crustacea and Cephalopoda being the most consumed in both females (%W?=?48.1, 16.0 and 31.4, respectively) and males (%W?=?33.9, 31.6 and 29.8, respectively). Higher diet diversity was observed in males than females, in immature individuals than mature ones, regardless of sex, as well as in spring in comparison to autumn and winter. Feeding intensity seemed to be influenced mainly by sex and maturity condition. No significant dietary overlap was observed for all possible combinations of the factors examined. Gut indices were compared between the two sexes with females showing statistically significantly higher median relative gut length, as well as a longer gut than males of the same length. Based on the diet composition, S. canicula can be considered a generalist predator consuming, with geographical differentiation, a wide variety of benthic taxa. The estimated fractional trophic level (τ?=?4.22) classified the species as a carnivore with a preference for Teleostei and Cephalopoda, thus confirming its key role in the food web.     

Detection of Bemisia tabaci remains in predator guts using a sequence-characterized amplified region marker

Bemisia tabaci (Gennadius) (Homoptera: Aleyrodidae) B biotype is an invasive species (biotype) in China. In order to understand the role that native natural enemies might play in its control, techniques were developed for detecting B. tabaci DNA within the gut of predators. A species-specific DNA fragment, ca. 350 bp, was identified by random amplified polymorphic DNA analysis. This fragment was absent in other closely related or co-occurring prey species, cotton, and other select predator species. After cloning and sequencing the fragment, one pair of sequence-characterized amplified region (SCAR) primers was developed, which amplified a single band of 240 bp. Specificity tests performed with the primers showed the presence of the 240-bp band for B. tabaci in all developmental stages and both sexes, in adult Propylaea japonica (Thunberg) (Coleoptera: Coccinellidae) fed on B. tabaci nymphs in the laboratory, and in predators collected in cotton fields. Following consumption of a single red-eyed B. tabaci nymph, prey DNA was detectable in 100% of P. japonica at t = 0, decreasing to 20% after 12 h of digestion, and no B. tabaci DNA detected at t = 24 h. In total, we analyzed the gut contents of 185 field-collected predators, representing four different orders. All nine field-collected predator species (namely, P. japonica, Harmonia axyridis, Scymnus hoffmanni, Coccinella septempunctata, Orius sauteri, Chrysopa pallens, Chrysopa formosa, Erigonnidium graminicolum, and Neoscona doenitzi) contained DNA from B. tabaci and are assumed predators of this pest insect. Overall, the B. tabaci was eaten by more than 50% of field-collected predator individuals, including larvae of the coccinellids (P. japonica and H. axyridis) and lacewings (C. pallens and C. formosa) and adults of O. sauteri and the spiders (E. graminicolum and N. doenitzi). There was a trend of a higher percentage of larval than adult coccinellids and lacewings that preyed on B. tabaci in the field. This study provides a framework for the future use of molecular gut content analysis in arthropod conservation ecology and food web research, with considerable potential for quantifying threats to invasive or endemic pest species in China and elsewhere.     

An ecological study of Phaenocora unipunctata (Örsted) (Turbellaria; Rhabdocoela): predator-prey interrelationships

The diet of P. unipunctata living in an English pond was investigated by examination of the gut contents of field-collected specimens, by a serological method and by laboratory experiments. Tubificids, and to a lesser extent lumbriculids, are the preferred food of small and large flatworms. In the laboratory damaged Cladocera and Chironomidae were fed upon to a very limited extent and in the serological tests a few flatworms gave a positive reaction with anti-Cladocera and anti-Chironomidae sera, but it is unlikely that these taxa are preyed upon extensively in the field. Communal feeding occurs. Algae and Protozoa are not eaten. P. unipunctata has no competitors for the oligochaete resource in the pond.Predators of the flatworm were determined mainly by laboratory experiments. Only the larvae and adults of Dytiscus attacked a few specimens. It is unlikely that flatworm and its cocoons have any serious predators in the pond.     

Indiscriminate Feeding by a Predatory Stonefly (Plecoptera: Perlidae) in a Tropical Asian Stream

The diet of an undescribed species of Kamimuria was investigated in Tai Po Kau Forest Stream, Hong Kong, by comparing larval gut contents with the array of available prey living on and among cobble substrates. Diets were dominated by chironomids and philopotamid caddisflies, with Baetidae, Heptageniidae, Hydropsychidae and Simuliidae comprising secondary dietary items. These six taxa made up 94% of the prey individuals eaten by Kamimuria. Data analysis using a selectivity index revealed that these stoneflies fed indiscriminately, eating individual prey taxa in proportion to their availability in the environment. Large and small Kamimuria exploited essentially the same prey. A comparison of the diet of Kamimuria with the diets of four sympatric Odonata indicated that the degree of interspecific similarity was determined by the extent of overlap in microhabitat use. Diets of Euphaea decorata (Zygoptera) larvae, which live under cobbles, were most similar to Kamimuria. This is the first – albeit limited – study of the gut contents of a tropical Asian stonefly. The results suggest that these predators have the potential to limit benthic invertebrate abundance but, because Kamimuria larvae feed unselectively, community structure may not be affected by their activities.     

Laboratory rearing of huhu,Prionoplus reticularis (Cerambycidae): insights into the gut microbiome

We developed a laboratory rearing method for huhu grubs, Prionoplus reticularis White (Coleoptera: Cerambycidae), on defined cellulose (cotton) and lignocellulose (pine) diets. Huhu grubs were shown to both gain weight and eventually undergo metamorphosis on these diets, two indications of successful use of the substrates for healthy growth. Since insects typically rely on their gut microbiome to assist in nutrient assimilation this rearing method was used to study the gut microbiome of P. reticularis, using the frass produced as a proxy for the gut contents. In this preliminary study patterns of fungal community diversity in frass suggest that their composition is significantly influenced by diet; however, the influence of diet on bacterial community diversity was less clear. Results do demonstrate the potential of the experimental model for studying shifts in the gut microbiome induced by diet change. This approach could prove essential in identifying microorganisms, or consortia, involved in the breakdown of lignocellulose.     

Stream flow and predation effects on the spatial dynamics of benthic invertebrates

Field experiments were carried out to determine the influence of predation and prey movements on the accumulation of prey in enclosures. Experimental enclosures permitted exchange of prey with the benthos, but not of the large, predatory larvae of the caddisfly, Plectrocnemia conspersa (Curtis). Unseasonally heavy rainfalls during the experiment resulted in high flows and enabled us to examine the effects of a major, abiotic disturbance on invertebrate spatial dynamics. Prey colonization rates of cages without predators were determined in nine 24 h periods. Colonization rates increased exponentially with flow and were species-specific, depending on dispersal behaviour. Prey accumulation and predator impacts were measured in cages, with and without P. conspersa larvae, placed in the stream for 1, 2 or 3 weeks. Prey densities in cages increased with exposure time, but increases were not gradual and depended on flow regime. Flow was reduced within cages and they accumulated large numbers of invertebrates during high discharge. Analogous, naturally occurring refugia in the stream channel could be important for the recovery of lotic communities after major disturbances. Overall, prey densities were lowest in cages with predators. For fast colonizers, predation effects were detectable early in the experiment, but quickly obscured thereafter by continuous exchange of prey. For slow colonists, predation effects were detectable later, but persisted longer. Consumption rates for P. conspersa varied with prey density and flow regime. We suggest that the spatial dynamics of benthic invertebrates, especially as they are influenced by stochastic events, are important in understanding and detecting predation effects in stream communities.     

Coupling of canopy and understory food webs by ground‐dwelling predators

Understanding food‐web dynamics requires knowing whether species assemblages are compartmentalized into distinct energy channels, and, if so, how these channels are structured in space. We used isotopic analyses to reconstruct the food web of a Kenyan wooded grassland. Insect prey were relatively specialized consumers of either C₃ (trees and shrubs) or C₄ (grasses) plants. Arboreal predators (arthropods and geckos) were also specialized, deriving c. 90% of their diet from C₃‐feeding prey. In contrast, ground‐dwelling predators preyed considerably upon both C₃‐ and C₄‐feeding prey. This asymmetry suggests a gravity‐driven subsidy of the terrestrial predator community, whereby tree‐dwelling prey fall and are consumed by ground‐dwelling predators. Thus, predators in general couple the C₃ and C₄ components of this food web, but ground‐dwelling predators perform this ecosystem function more effectively than tree‐dwelling ones. Although prey subsidies in vertically structured terrestrial habitats have received little attention, they are likely to be common and important to food‐web organization.     

EVIDENCE FOR COMPETITIVE RELEASE IN SIMPLIFIED SAXICOLOUS LICHEN COMMUNITIES

Saxicolous cryptogam communities were sampled quantitatively on two Potomac River island habitats in June of 1980. As a result of air pollution stress, the community on one island was found to be much simpler than that found on the other island. Two relatively pollution-tolerant foliose lichen species, Xanthoparmelia conspersa and Pseudoparmelia baltimorensis, were found to dominate the communities on both islands. An examination of niche breadth and position along a light intensity gradient demonstrated that P. baltimorensis was most frequent at low light intensities and X. conspersa was most frequent at high light intensities. However, X. conspersa exhibited a niche shift toward intermediate light intensities in the species-poor community, likely the result of reduced competitor diversity in this community since the intermediate light intensities supported the greatest number of species in the species-rich community. Niche overlap between the two species was found to occur at lower light intensities in the species-poor community, suggesting that X. conspersa is more likely to appropriate intermediate light intensities in this community. The significance of competition as a regulatory factor in lichen communities has not been fully appreciated. Since lichens and other cryptogams are frequently used as indicators of environmental quality, competitive processes in naturally occurring lichen communities must be thoroughly understood before changes in species distribution that apparently result from disturbance can be properly interpreted.     

18S rRNA V9 metabarcoding for diet characterization: a critical evaluation with two sympatric zooplanktivorous fish species

The potential of the 18S rRNA V9 metabarcoding approach for diet assessment was explored using MiSeq paired‐end (PE; 2 × 150 bp) technology. To critically evaluate the method′s performance with degraded/digested DNA, the diets of two zooplanktivorous fish species from the Bay of Biscay, European sardine (Sardina pilchardus) and European sprat (Sprattus sprattus), were analysed. The taxonomic resolution and quantitative potential of the 18S V9 metabarcoding was first assessed both in silico and with mock and field plankton samples. Our method was capable of discriminating species within the reference database in a reliable way providing there was at least one variable position in the 18S V9 region. Furthermore, it successfully discriminated diet between both fish species, including habitat and diel differences among sardines, overcoming some of the limitations of traditional visual‐based diet analysis methods. The high sensitivity and semi‐quantitative nature of the 18S V9 metabarcoding approach was supported by both visual microscopy and qPCR‐based results. This molecular approach provides an alternative cost and time effective tool for food‐web analysis.     

The natural diet of the Notonectidae: field trials using electrophoresis

ABSTRACT.

• 1 Field trials were conducted on populations of two sympatic species of the waterbug Notonecta (Hemiptera: Heteroptera), to examine their natural diet using the electrophoretic method of gut contents analysis.
• 2 Fingerprint esterase bands were identified from thirty-three potential aquatic prey types; gut contents of different instars of both species of Notonecta from the field were analysed.
• 3 The level of prey identification possible ranged from 73% in fifth instar N.glauca L. to 100% in third instar N.viridis Delcourt.
• 4 Type A errors, where no prey remains were detected from a full gut, were found in only 3% of the specimens analysed.
• 5 Data on gut states, the number of prey types per gut and details of aquatic prey found in the diet of different instars of field-collected Notonecta are presented.
• 6 These results are compared with previous data on notonectid diets, and the relative merits of different methods of diet analysis are discussed.

     

Diets of syntopic finescale dace,Phoxinus neogaeus,and northern redbelly dace,Phoxinus eos: a reflection of trophic morphology

Synopsis We examined relative abundance, distribution, and gut contents of Phoxinus eos and P. neogaeus in a small northern Michigan bog lake. P. eos were usually 5–100 x more abundant than P. neogaeus, but both species were more abundant near the lake margin than offshore. Both species fed primarily on algae and invertebrates associated with the bog mat, but differences in diet were associated with differences in trophic morphology. As expected, because of its relatively longer intestine and smaller mouth, P. eos consumed relatively more plant matter, especially green algae, and fewer macroinvertebrates than P. neogaeus. These dietary conclusions were supported by analysis of two independent data sets. Further work is needed to discriminate between the effects of body size and trophic morphology on diet.