Differences In Prey Consumption Research Articles

Control of two-spotted spider mite, Tetranychus urticae, on strawberry by integrating with cyetpyrafen and Phytoseiulus persimilis

The two-spotted spider mite (TSSM, Tetranychus urticae Koch) is a significant agricultural pest, particularly in strawberries. Management of TSSM has traditionally relied on synthetic acaricides, but to mitigate dependency on these chemicals, the control of TSSM on strawberry is often combined with biological control measures and chemical control strategies. The predatory mite, Phytoseiulus persimilis, is a promising biological control agent, preying on all TSSM developmental stages. In this study, we examined the toxicity of six common acaricides on TSSM and P. persimilis, and cyetpyrafen was selected due to its highest relative toxicity value. Then, we examined the compatibility of cyetpyrafen with P. persimilis for TSSM management on strawberries. The results suggested that cyetpyrafen revealed no substantial differences in prey consumption or longevity when compared to the control, though minor effects on the development durations of protonymphs and deutonymphs were noted in the subsequent generation. Additionally, cyetpyrafen's toxicity on key pollinators, such as Apis mellifera and Bombus terrestris, was found to be low. Thus, an integrated strategy combining cyetpyrafen (0.83 mg/L) with P. persimilis (predator–prey ratio of 1:30) was examined under laboratory and field conditions. Laboratory trials demonstrated a reduction in mites per leaf from 32.72 to 14.50 within 3 days, correlating to a 70.23% control efficiency. This efficacy increased to 96.04% by day 9 and was sustained until the experiment concluded on day 27. Field trials similarly showed a reduction in TSSM from 53.93 to 9.63 mites/leaf by day 6, achieving an 83.64% control efficiency, and culminated in a 98.46% reduction by day 10. These findings suggested that an integrated approach utilizing cyetpyrafen in conjunction with P. persimilis can be an effective alternative for TSSM management on strawberry plants.

Mercury Isotope Values in Shoreline Spiders Reveal the Transfer of Aquatic Mercury Sources to Terrestrial Food Webs.

The transfer of aquatic contaminants, including mercury (Hg), to terrestrial food webs is an often-overlooked exposure pathway to terrestrial animals. While research has implemented the use of shoreline spiders to assess aquatic to terrestrial Hg transfer, it is unclear whether Hg sources, estimated from isotope ratios, can be successfully resolved to inform site assessments and remedy effectiveness. To examine aquatic to terrestrial Hg transfer, we collected shoreline spiders (Tetragnatha spp.) and aquatic insect larvae (suborder Anisoptera) across a mosaic of aquatic and shoreline habitats in the St. Louis River and Bad River, tributaries to Lake Superior. The fraction of industrial Hg in sediments was reflected in the δ202Hg values of aquatic dragonfly larvae and predatory fish, connecting benthic Hg sources to the aquatic food web. Shoreline spiders mirrored these aquatic Hg source signatures with highly positive correlations in δ202Hg between tetragnathids and dragonfly larvae (r2 = 0.90). Further assessment of different spider taxa (i.e., araneids and pisaurids) revealed that differences in prey consumption and foraging strategies resulted in isotope differences, highlighting the importance of spider taxa selection for Hg monitoring efforts.

Functional and Behavioral Responses of the Natural Enemy Anthocoris nemoralis to Cacopsylla pyri, at Different Temperatures

Anthocoris nemoralis is the dominant predator of pear sucker (Cacopsylla pyri) in the UK. Anthocoris nemoralis migrates into orchards in spring or is introduced as a biocontrol agent, reaching peak population levels in July-August, contributing to effective control of summer pear sucker populations. However, due to temperature dependent development and metabolism there are concerns that C. pyri populations or feeding rates may increase due to changing climatic conditions. Thus, how A. nemoralis responds to temperature, impacts its ability as a biocontrol agent. Functional response assays, monitoring attack rate and handling time of A. nemoralis and behavioral assays, using Ethovision tracking software occurred, to assess the impact of temperature on predation. Experiments were conducted at current and future July-August mean temperatures, predicted using RCP4.5 and RCP8.5 (medium and high, representative concentration pathway) emissions scenarios, using 2018 UK Climate Projections (UKCP18). All treatments demonstrated a Type II functional response, with female anthocorids demonstrating shorter handling times and higher attack rates than males. Males showed longer prey handling times at 18 °C compared to 23 °C and more time was spent active at lower temperatures for both sexes. Females did not show significant differences in attack rate or handling time in response to temperature. Overall prey consumption was also not significantly affected by temperature for either sex. This study suggests that anthocorids are likely to remain effective natural enemies under future predicted temperatures, due to non-significant differences in prey consumption.

Effects of sika deer density on the diet and population of red foxes

Recent studies have shown that an increase in the population size of sika deer (Cervus nippon) decreases the abundance of rodents but increases that of several invertebrates (Scarabaeidae, Rhaphidophoridae, and earthworms) outside a deep-proof fence in Oku-Nikko, Japan. Therefore, the diet of red foxes (Vulpes vulpes) feeding on these animals is expected to vary according to changes in prey abundance. As red foxes also scavenge deer carcasses, an increase in the number of deer is expected to lead to changes in the red fox diet. In this study, the diet and sightings of red foxes inside and outside the fence were compared. Generalized linear mixed models indicate that the sika deer remains, ground-dwelling insects (Scarabaeidae and Rhaphidophoridae as a group, and Carabidae), and earthworms increased in the fox diet outside the fence, while the ingestion of voles decreased. The difference in prey consumption by red foxes was probably caused by differences in prey availability inside and outside the fence or the presence of available alternative food. These results suggest that red foxes demonstrate dietary plasticity in areas where habitat structure has been substantially modified by deer grazing. Although the abundance of voles, the primary food of red foxes, decreased outside the fence, the sighting rates of red foxes obtained by spotlight count were not significantly different between inside and outside the fence, suggesting that the presence of the others increased or available alternative food may have compensated for the negative effects of decreasing vole abundance.

Gut contents from multiple morphs of lake trout (Salvelinus namaycush) at two offshore shoals in Lake Superior

Four lake trout, Salvelinus namaycush, Walbaum 1792 morphs occur in Lake Superior: lean, siscowet, humper, and redfin. Diets of lean and siscowet have been relatively well described. However, less is known about diets of humper and redfin, and overall few studies have been conducted at offshore shoals. We compared gut content data among mature (357–867 mm) sympatric lake trout morphs caught at two offshore shoals in Lake Superior, Stannard Rock and Superior Shoal, in 2013 and 2014 (total n = 416). All morphs were caught in shallow (<50 m), mid (50–100 m), and deep (>100 m) strata. Invertebrates made up a greater portion of the stomach contents than did fish for all morphs by both percent occurrence and proportional biomass, and Mysis was the primary invertebrate consumed by all morphs at both sites. Coregonus spp. and deepwater sculpin, Myoxocephalus thompsonii were the most commonly consumed fish. Humper had the highest average proportional biomass of deepwater sculpin and had no other identifiable species of fish in their guts. Biomass of fish in redfin guts was highest for Coregonus spp., followed by similar amounts of deepwater sculpin and burbot, Lota lota. Diet overlap among morphs was high, and differences in prey consumption between sites are likely related to prey availability. Additional study is needed to determine if differences in trophic ecology between humper and other morphs are sufficient to support concurrent stocking of multiple morphs, particularly in light of recent declines in native prey fishes, especially Coregonus spp., in the Laurentian Great Lakes.

Macrolophus pygmaeus (Hemiptera: Miridae) foraging on tomato leaves from different plant strata

This study investigates the foraging activity of the generalist predator Macrolophus pygmaeus (Rambur) (Hemiptera: Miridae) on tomato leaves of different vertical plant strata (apex, top, middle and lower). On a leaflet of each tested leaf, ten 2nd instar nymphs of the aphid Myzus persicae were established with the aid of harmless glue, as prey. It was observed that prey consumption was highest on the lower leaves. There was no significant difference in prey consumption between middle and top leaves but it significantly reduced on the apex leaves as compared to the top and the lower leaves. Behavioural observations were conducted to assess the time budgets (i.e. time spent in each activity such as searching, resting, grooming) of the foraging predator on leaves of each plant strata. The predator spent significantly more time in grooming on apex than on lower leaves whereas it showed a higher tendency to fall off from the apex leaves than the leaves of the other plant strata. The apex leaves had the highest trichome density and this may impede movement of the predator. In the third experiment, the prey consumption of M. pygmaeus nymphs was reduced with the increase of distance between its release point and the prey patch on a tomato plant. In conclusion, M. pygmaeus nymphs are most efficient in foraging on the middle or lower leaves of young tomato plants whereas their prey searching efficiency is influenced by the distance between their release point and the prey patch. Therefore, the efficacy of M. pygmaeus nymphs in pest control may be benefited if released close to prey patches but not on the apex leaves.

Gene expression characterizes different nutritional strategies among three mixotrophic protists

Mixotrophic protists, i.e. protists that can carry out both phototrophy and heterotrophy, are a group of organisms with a wide range of nutritional strategies. The ecological and biogeochemical importance of these species has recently been recognized. In this study, we investigated and compared the gene expression of three mixotrophic protists, Prymnesium parvum, Dinobyron sp. and Ochromonas sp. under light and dark conditions in the presence of prey using RNA-Seq. Gene expression of the obligately phototrophic P. parvum and Dinobryon sp. changed significantly between light and dark treatments, while that of primarily heterotrophic Ochromonas sp. was largely unchanged. Gene expression of P. parvum and Dinobryon sp. shared many similarities, especially in the expression patterns of genes related to reproduction. However, key genes involved in central carbon metabolism and phagotrophy had different expression patterns between these two species, suggesting differences in prey consumption and heterotrophic nutrition in the dark. Transcriptomic data also offered clues to other physiological traits of these organisms such as preference of nitrogen sources and photo-oxidative stress. These results provide potential target genes for further exploration of the mechanisms of mixotrophic physiology and demonstrate the potential usefulness of molecular approaches in characterizing the nutritional modes of mixotrophic protists.

Living in a same microhabitat should means eating the same food? Diet and trophic niche of sympatric leaf-litter frogs Ischnocnema henselii and Adenomera marmorata in a forest of Southern Brazil.

In this study we analyzed diet composition, niche breadth and overlap of the two leaf-litter frogs Ischnocnema henselii and Adenomera marmorata. Frogs were collected in an Atlantic Rainforest area in the Reserva Natural Salto Morato, in Paraná State, Southern Brazil, using plots of 16 m2 established on forest floor. Ischnocnemahenselii consumed18differenttypes of prey and the diet of this species was composed predominantly by Hymenoptera (Formicidae) (15.4%), Araneae (13.83%), Orthoptera (6.15%) and Opiliones (6.15%), whereas Adenomera marmorata consumed 15 different types of prey and its diet was composed mainly by Hymenoptera (Formicidae) (45.7%), Acari (31.8%) and Blattodea (14.8%). The niche breadth of I.henselii was BA = 0.43 and that of A. marmorata was BA = 0.19. The diet of the two sympatric species of leaf-litter frogs was basically composed by arthropods and the trophic niche overlap among them did not differ from expected at random. The differences in prey consumption should potentially facilitate the coexistence of two sympatric frogs on the forest floor. Possibly, this difference of prey consumption partly reflects differences in jaw width, species-specific body size of the two species and the period of activity of these two species.

담배장님노린재, Nesidiocoris tenuis (Hemiptera: Miridae)의 먹이 섭취량에 대한 식물체 흡즙의 영향

담배가루이 등 방제용 천적으로 유망한 담배장님노린재(Nesidiocoris tenuis)의 줄알락명나방(Ephestia kuehniella) 알 섭취 전 먹은 식물성 먹이에 따라 줄알락명나방알 섭취량이 달라지는지를 알아보기 위해 포트에 재식된 참깨, 파프리카, 솜에 적신 물을 각각 하루 동안 섭식하게 한 담배장님노린재에게 냉동한 줄알락명나방의 알을 공급하고 하루 동안 섭취한 알의 개수를 비교하였다. 파프리카를 먼저 섭식한 담배장님노린재가 가장 많은 <TEX>$55.7{\pm}30.19$</TEX>개의 줄알락명나방 알을 섭취한 것으로 나타났으며, 참깨를 먼저 섭식한 경우에는 줄알락명나방 알을 <TEX>$24.2{\pm}34.70$</TEX>개 섭취하였고, 물을 먼저 섭식한 경우에는 줄알락명나방 알을 <TEX>$49.2{\pm}30.58$</TEX>개 섭취하였다. 파프리카와 물을 먼저 섭식한 경우 통계적인 유의차는 보이지 않았다. 그러나 참깨를 먼저 섭식한 경우 파프리카 또는 물을 먼저 섭식한 경우에 비해 더 적은 수의 줄알락명나방의 알을 섭취한 것으로 나타났다. This study was performed to understand whether host-plant feeding had an influence on subsequent prey consumption in the zoophytophagous mirid Nesidiocoris tenuis, which has the potential for biological control of greenhouse whiteflies. Potted plants of paprika and sesame and cotton balls soaked with water were provided to the test insects for 24 h, then, frozen eggs of Ephestia kuehniella were presented to adult mirids for 24 h, and the number of eggs consumed by them was counted. No significant difference in prey consumption was observed between the mirids previously provided with water (<TEX>$49.2{\pm}30.58$</TEX> eggs) or paprika (<TEX>$55.7{\pm}31.19$</TEX> eggs), whereas those previously fed with sesame ate significantly less prey (<TEX>$24.2{\pm}34.70$</TEX> eggs) than the mirids that were provided with paprika or water.

The effects of turbidity on prey consumption and selection of zooplanktivorous Gasterosteus aculeatus L.

It is well documented that reduced visibility caused by elevated turbidity can affect feeding of fish, yet the extent to which selective zooplanktivory is altered in turbid conditions remains ambiguous. In this study, we examined the influence of natural sediment-induced turbidity on the overall prey consumption and selective predation of a common brackish water littoral zooplanktivore, the particulate feeding three-spined stickleback (Gasterosteus aculeatus L.). We hypothesized that the effects of turbidity on prey consumption and prey type selection would be pronounced due to the vision-oriented feeding of this species and that these effects would differ between genders. Using aquarium experiments with three different groups of cladocerans and copepods varying in size and behavior, we studied prey consumption and selectivity of this key planktivore in varying turbidity treatments. Our results indicated significantly decreased total prey consumption in the high turbidity treatments, as well as altered selective feeding on copepods and an enhanced preference for larger cladocerans. We found gender-dependent differences in prey consumption, which are consistent with observations of other visually feeding fish with sexual size dimorphism. We conclude that high turbidity, such as that occurring in shallow coastal areas, may affect selective feeding in vision-oriented zooplanktivores and that these effects may be gender-related.

Diet of Ameerega braccata (Steindachner, 1864) (Anura: Dendrobatidae) from Chapada dos Guimarães and Cuiabá, Mato Grosso State, Brazil

The understanding of feeding habits is important for anurans in general, both from an ecological and a phylogenetic perspective. For diurnal poison frogs belonging to the Dendrobatidae family, diet aspects play a crucial role in their defense and survival. Herein, we investigated feeding habits, foraging behaviour, and overall effects of habitat, sex, and body size on the diet of individuals of Ameerega braccata, a poorly known dendrobatid species. Specimens were observed and collected in the type-locality, Chapada dos Guimarães, and in the neighbouring municipality of Cuiabá, both in the State of Mato Grosso, Midwestern Brazil. The most important prey categories for A. braccata were Formicidae, Isoptera, and Acari, whose representatives were caught during active foraging. Individuals from Chapada dos Guimarães population consumed more Acari but fewer Isoptera than individuals from Cuiabá. Despite this, niche breadth values were narrow and similar for the two populations. Individuals from two distinct habitats (campo sujo and cerrado stricto sensu) showed differences in their diet, probably as an effect of differential prey availability. Females consumed more Isoptera than males. The number of prey categories used as food was not influenced by the variation of body size of the target species. However, the abundance and the volume of consumed Acari were statistically correlated with body size. The main results suggest that Ameerega braccata has a narrow niche breadth, as well as a specialised diet in ants, termites, and mites, which reinforces the hypotheses of close association between Acari consumption and the presence of skin toxic alkaloids, already found in other species of Dendrobatidae. Although differences in prey consumption between sexes are uncommon among poisonous frogs, differences in the diet composition between age classes, which probably reduce intraspecific competition, are frequently reported.

Mercury Concentration in Two Estuarine Fish Populations across a Seasonal Salinity Gradient

AbstractMercury (Hg) cycling in estuaries is complex, and little is known about the extent of Hg bioaccumulation in the ecologically diverse fishes that inhabit coastal areas. Using tissue analysis combined with otolith microchemistry, analysis of Hg concentration in common prey species, diet analysis, and age‐and‐growth analysis, we investigated seasonal and spatial trends of Hg accumulation in largemouth bass Micropterus salmoides and southern flounder Paralichthys lethostigma inhabiting the Mobile—Tensaw River Delta, Alabama. The Hg concentrations in largemouth bass (which are known to have high site fidelity) were lowest at downstream, low‐salinity estuarine areas and highest at upstream freshwater areas. Conversely, southern flounder, which have a highly variable migratory life history across salinity gradients, had Hg concentrations that were similar across the study area and lower than those for largemouth bass. Both largemouth bass and southern flounder had negative relationships between individual salinity exposure (as indicated by otolith strontium: calcium ratios) and tissue Hg concentration, although considerable variability existed. Concentrations of Hg in two common prey species, the bluegill Lepomis macrochirus and blue crab Callinectes sapidus, suggested that vertebrate prey had higher Hg concentrations than invertebrate prey. Largemouth bass upstream consumed a higher proportion of vertebrates than those downstream, so differences in prey consumption may partially explain Hg concentration differences across the salinity gradient. However, additional research is required to understand the mechanism responsible for the negative relationship between Hg concentration and salinity exposure.

Diets of three sympatric Neotropical small cats: Food niche overlap and interspecies differences in prey consumption

Dietary investigations of sympatric felids are means for understanding how closely related species deal with food resources in a potentially competitive scenario. The diets of the oncilla Leopardus tigrinus, the jaguarundi Puma yagouaroundi and the ocelot Leopardus pardalis were studied through the analysis of scats in Araucaria Pine Forest with Natural Grasslands of southern Brazil. Small mammals comprised the bulk of the diets of the three felids, followed by birds and reptiles. The smallest food-niche overlap index was 0.84, indicating that these felids shared an important portion of their food resources. Inter-species differences were detected in the consumption of the most frequent rodent prey; L. tigrinus was the only species that consumed all the most frequent rodent prey differently from the rate expected from their abundances. Although these findings suggest competitive interactions, with the oncilla being the most subordinate species, further experimental investigations are necessary to elucidate more precisely how these syntopic felids coexist. The effects of sample size and its influences on the evaluation of the diets of the felids, especially of the ocelot, are discussed. We compare our data to a previous study in the same area, to account for the possible influences of biased sampling and uneven distribution of food resources on the diet of the ocelot. The opportunistic feeding behavior and the abundance of their primary prey (cricetid rodents) seem to allow these small cats to be resilient despite severe anthropogenic disturbance in the study area. We further suggest guidelines for future studies in the study region, in order to understand the dynamics of mammalian carnivores demography.

Cheliped morphological variation of the intertidal crab Eriphia verrucosa across shores of differing exposure to wave action

Understanding the effects of predator–prey interactions at a community level requires robust information on the mechanisms determining these interactions at the individual level. Here we use the intertidal crab Eriphia verrucosa (Forskål) as a model species to examine patterns of association between functional morphology (cheliped size and form) and patterns of prey consumption on shores of differing exposure to wave action. The size and form of the cheliped of crabs are known to be related to feeding performance and thus influence the outcomes for prey assemblages. Multivariate analyses showed that the claw size and shape of E. verrucosa varied between shores of differing exposure to wave action. Individuals from exposed locations had larger claws than those from sheltered locations. This shift in size was accompanied by differences in the composition of stomach contents between locations. Crabs from exposed shores had ∼ 55% more hard shell prey (mussels and limpets) in their diet than those from sheltered shores. Crabs were more abundant on sheltered shores, but those from exposed locations were larger in carapace width. The relative abundance of prey varied between shores of differing exposure. Patterns of claw functional morphology provided a mechanistic explanation for the differences in prey consumption along the wave exposure gradient, although it remains to be tested whether there is a phenotypic plasticity response of crab claw to patterns of prey consumption. The interaction between prey abundance and morphology of the cheliped will likely shape the diet of this crab species, and this may have implications for the relative impact of this predator between shores of differing exposure.

Trophic level and overlap of sea lions (Zalophus californianus) in the Gulf of California, Mexico

AbstractStable isotope and scat analyses were used in concert to determine trophic level and dietary overlap among California sea lions from different rookeries in the Gulf of California. Isotopic analysis of the fur of sea lion pups revealed differences in δ15N and δ13C values among rookeries during the breeding season. Mean δ15N and δ13C values varied from 20.2‰ to 22.4‰ and from −15.4‰ to −14.0‰, respectively. The pattern of differences among rookeries was similar between years in most cases. Isotopic variations among rookeries were associated with differences in prey consumption. There was a significant correlation between δ15N value and trophic level, as determined by scat analysis. Joint application of isotopic and scat analyses allowed us to identify how the feeding habits of sea lions vary with location. Our results suggest the presence of spatial structure in available prey as well as the localized use of prey by sea lions across the Gulf of California.

Spatio-temporal changes in gut contents and stable isotopes in two deep Mediterranean pandalids: influence on the reproductive cycle

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 355:219-233 (2008) - DOI: https://doi.org/10.3354/meps07260 Spatio-temporal changes in gut contents and stable isotopes in two deep Mediterranean pandalids: influence on the reproductive cycle Emanuela Fanelli*, Joan E. Cartes Institut de Ciències del Mar de Barcelona, Consejo Superior de Investigaciones Cientificas, Passeig Marítim de La Barceloneta 37–49, 08003 Barcelona, Spain *Email: efanelli@icm.csic.es ABSTRACT: The feeding habits of the 2 Plesionika species occurring around the Balearic Islands (western Mediterranean) were examined. Samples were taken with a bottom trawl from depths between 247 and 752 m from August 2003 to June 2004 at 2 sites (Cabrera and Sóller) off the island of Mallorca. Both species preferentially exploited mesopelagic resources but the shallower living P. heterocarpus, which inhabits the shelf-slope break, also consumed benthic organisms (e.g. polychaetes, bivalves, tanaids). Spatio-temporal changes were evident in the diet of the 2 pandalids. In P. heterocarpus, 2 seasonal groups were revealed by nMDS analysis, one summer–autumn, the other winter–spring. Differences in prey consumption were observed between Cabrera and Sóller samples, with a temporal shift in the dominance of some prey between the 2 areas. The diet of P. heterocarpus was significantly correlated with geographical (e.g. latitude, depth), chemico-physical variables (mainly those related to sediment characteristics) and biological features (e.g. maturity stages, sex) of the species. Correlation between percentage of mature females and caloric content of prey in the stomach did not show any clear seasonal pattern; also trophic level did not change throughout the year (δ15N = 7.87‰ ± 0.17). Temporal changes in diet composition were stronger in the deeper pandalid P. martia and strictly related to its reproductive pattern. Three groups were revealed by multivariate analysis: (1) a summer group (August and September samples), (2) an autumn–winter group (November and February), characterized by high predation on gelatinous plankton, salps, hyperiids and pelagic molluscs and (3) a spring group, in which predation was directed to higher energy prey such as euphausiids and decapods. The higher percentage of mature females observed in spring was correlated with the increase in energy requirements in the pre-spawning period. Stable isotope analysis revealed a stronger seasonality for P. martia than for P. heterocarpus. An abrupt decrease in trophic level (δ15N) and an analogous enrichment in δ13C values were observed in February. This trend may be related to various factors, among others a higher consumption of refractory material (e.g. marine snow) in winter, when mesopelagic resources are scarcer, changes in the whole zooplanktonic and suprabenthic communities due to phytodetritus input of low δ15N /high δ13C values, and possible reproductive migration to deeper waters. KEY WORDS: Pandalid shrimps · Diet · Reproduction · Seasonality · Environmental variables · Benthopelagic fauna · Stable isotope analysis Full text in pdf format Supplementary appendices PreviousNextCite this article as: Fanelli E, Cartes JE (2008) Spatio-temporal changes in gut contents and stable isotopes in two deep Mediterranean pandalids: influence on the reproductive cycle. Mar Ecol Prog Ser 355:219-233. https://doi.org/10.3354/meps07260Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 355. Online publication date: February 26, 2008 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2008 Inter-Research.

Natural Diet of an Australian Freshwater Pipefish

AbstractGlobally, the family Syngnathidae (seahorses and pipefish) is recognized as being both under threat from anthropogenic pressures and poorly studied. Of the 47 species that are listed on the IUCN Red List, 33 are currently listed as ‘data deficient’, with inadequate information available to make an assessment of their risk of extinction. Within Australia, this has prompted environmental assessments of specific fisheries, as well as a number of recent ecological studies of marine syngnathids. However, no work has been published on the continent’s four freshwater species. To begin to remedy this, a thorough analysis of the feeding habits of one such species was conducted. Twenty-two specimens of Hippichthys heptagonus Bleeker, 1849 were collected from the Mulgrave River in north Queensland. Dissection and subsequent analysis revealed that microcrustaceans comprised the vast majority of the species diet, with calanoid and cyclopoid copepods being by far the most prevalent prey items (66%). Dipteran, as well as ephemeropteran, larvae were moderately abundant (5% and 10%), and made a notable contribution to the volume of the average diet (16% and 12%). A percent principal component analysis of the volume data reinforced these findings. The first factor accounted for 69.7% of the observed variation, with largest factor loading (0.88) belonging to copepods. there were no significant differences in prey consumption Between genders, but, the percent volume of copepod prey significantly higher in adults was than in juveniles (Mann-Whitney’s U: P &lt; 0.01). These findings indicate that H. heptagonus is primarily a predaceous planktivore, with a specialized diet that is comparable to coastal marine syngnathids. Also, the prevalence of a single prey type suggests that the H. heptagonus occupies a narrow ecological niche, and that its distribution within the watershed may be limited by prey availability.

Variation in Prey-resource Utilization and Oral Jaw Gape Between two Populations of Largemouth Bass, Micropterus Salmoides

Ontogenetic changes in diet and jaw gape were compared between two indigenous populations of largemouth bass, Micropterus salmoides, to test the hypothesis that ecomorphology varies among broadly distributed fish populations. Two hundred seventy-two temperate (southwestern Michigan) M. salmoides and 265 subtropical (east-central Florida) conspecifics were analyzed for food habits and oral jaw gape height and width. Percent volumetric contributions of four functional prey categories (plankton, insect, crustacean, and fish) were compared among fish-size classes to determine if interval-specific differences in prey consumption existed between populations. Subtropical M. salmoides shifted from feeding on plankton and macroinvertebrates to fish by 20 mm standard length (SL); and stopped consuming plankton by 29 mm SL. Temperate largemouth bass did not become piscivorous until 37 mm SL and continued utilizing plankton up to 69 mm SL. Following the onset of piscivory, 100–260 mm SL subtropical largemouth bass began utilizing more crustaceans than fish. In contrast, temperate M. salmoides consistently fed on fish following the onset of piscivory. Variations in food habits were associated with differences in gape size between temperate and subtropical populations. Temperate largemouth bass had significantly larger gape height (ANCOVA: F = 103.4; df = 1,536; p < 0.001) and width (ANCOVA: F = 47.0; df = 1,536; p < 0.001) than subtropical bass. Although piscivory is a well-known feature of M. salmoides, the ontogeny of piscivory may vary between populations. We hypothesize that interpopulation differences in jaw gape may be related to variations in prey-resource utilization.

Size-Dependent Mechanisms Influencing First-Year Growth and Winter Survival of Stocked Striped Bass in a Virginia Mainstream Reservoir

Abstract To explain the limited stocking success of fingerling striped bass Morone saxatilis in Smith Mountain Lake, Virginia, we examined the relationship between size-selective winter survival and length-dependent patterns in growth, food habits, prey fish availability, and lipid energy reserves during the first year of life in two successive years from 1994 to 1996. Length distributions of striped bass were unimodal at the time of stocking, and growth remained positive for all fish during both growing seasons. By the fall of both years, a bimodal length distribution had developed within the age-0 cohort, which then consisted of small-mode ( 180 mm) fish. The differential growth was attributed to size-dependent differences in prey consumption and diet quality. Small-mode striped bass maintained a mixed diet of invertebrates and small cyprinids, whereas fish in the larger mode were strictly piscivorous, consuming only age-0 alewives Alosa pseudoharengus. The disparity in food hab...

Ecological character displacement in Plethodon: biomechanical differences found from a geometric morphometric study.

Ecological character displacement describes a pattern where morphological differences between sympatric species are enhanced through interspecific competition. Although widely considered a pervasive force in evolutionary ecology, few clear-cut examples have been documented. Here we report a case of ecological character displacement between two salamander species, Plethodon cinereus and Plethodon hoffmani. Morphology was quantified by using linear measurements and landmark-based geometric morphometric methods for specimens from allopatric and sympatric populations from two geographic transects in south-central Pennsylvania, and stomach contents were assayed to quantify food resource use. Morphological variation was also assessed in 13 additional allopatric populations. In both transects, we found significant morphological differentiation between sympatric populations that was associated with a reduction in prey consumption in sympatry and a segregation of prey according to prey size. No trophic morphological or resource use differences were found between allopatric populations, and comparisons of sympatric populations with randomly paired allopatric populations revealed that the observed sympatric morphological differentiation was greater than expected by chance. The major trophic anatomical differences between sympatric populations relates to functional and biomechanical differences in jaw closure: sympatric P. hoffmani have a faster closing jaw, whereas sympatric P. cinereus have a slower, stronger jaw. Because salamanders immobilize prey of different sizes in different ways, and because the observed sympatric biomechanical differences in jaw closure are associated with the differences in prey consumption, the observed character displacement has a functional ecological correlate, and we can link changes in form with changes in function in this apparent example of character displacement.