Diet Reconstruction and Resource Partitioning of a Caribbean Marine Mesopredator Using Stable Isotope Bayesian Modelling

The trophic ecology of epibenthic mesopredators is not well understood in terms of prey partitioning with sympatric elasmobranchs or their effects on prey communities, yet the importance of omnivores in community trophic dynamics is being increasingly realised. This study used stable isotope analysis of ¹⁵N and ¹³C to model diet composition of wild southern stingrays Dasyatis americana and compare trophic niche space to nurse sharks Ginglymostoma cirratum and Caribbean reef sharks Carcharhinus perezi on Glovers Reef Atoll, Belize. Bayesian stable isotope mixing models were used to investigate prey choice as well as viable Diet-Tissue Discrimination Factors for use with stingrays. Stingray δ¹⁵N values showed the greatest variation and a positive relationship with size, with an isotopic niche width approximately twice that of sympatric species. Shark species exhibited comparatively restricted δ¹⁵N values and greater δ¹³C variation, with very little overlap of stingray niche space. Mixing models suggest bivalves and annelids are proportionally more important prey in the stingray diet than crustaceans and teleosts at Glovers Reef, in contrast to all but one published diet study using stomach contents from other locations. Incorporating gut contents information from the literature, we suggest diet-tissue discrimination factors values of Δ¹⁵N ≊ 2.7‰ and Δ¹³C ≊ 0.9‰ for stingrays in the absence of validation experiments. The wide trophic niche and lower trophic level exhibited by stingrays compared to sympatric sharks supports their putative role as important base stabilisers in benthic systems, with the potential to absorb trophic perturbations through numerous opportunistic prey interactions.     

Community assembly in Nothobranchius annual fishes: Nested patterns,environmental niche and biogeographic history

The assembly of local communities from regional species pools is shaped by historical aspects of distribution, environmental conditions, and biotic interactions. We studied local community assembly patterns in African annual killifishes of the genus Nothobranchius (Cyprinodontiformes), investigating data from 168 communities across the entire range of regionally co‐existing species. Nothobranchius are small fishes associated with annually desiccating pools. We detected a nested pattern of local communities in one region (Southern Mozambique, with Nothobranchius furzeri as the core and dominant species), but no nestedness was found in the second region (Central Mozambique, with Nothobranchius orthonotus being the dominant species). A checkerboard pattern of local Nothobranchius community assembly was demonstrated in both regions. Multivariate environmental niche modeling revealed moderate differences in environmental niche occupancy between three monophyletic clades that largely co‐occurred geographically and greater differences between strictly allopatric species within the clades. Most variation among species was observed along an altitudinal gradient; N. furzeri and Nothobranchius kadleci were absent from coastal plains, Nothobranchius pienaari, Nothobranchius rachovii, and Nothobranchius krysanovi were associated with lower altitude and N. orthonotus was intermediate and geographically most widespread species. We discuss implications for ecological and evolutionary research in this taxon.     

Metazoan parasites of African annual killifish (Nothobranchiidae): abundance,diversity, and their environmental correlates

Estimates of biodiversity and its global patterns are affected by parasite richness and specificity. Despite this, parasite communities are largely neglected in biodiversity estimates, especially in the tropics. We studied the parasites of annual killifish of the genus Nothobranchius that inhabit annually desiccating pools across the African savannah and survive the dry period as developmentally arrested embryos. Their discontinuous, non‐overlapping generations make them a unique organism in which to study natural parasite fauna. We investigated the relationship between global (climate and altitude) and local (pool size, vegetation, host density and diversity, and diversity of potential intermediate hosts) environmental factors and the community structure of killifish parasites. We examined metazoan parasites from 21 populations of four host species (Nothobranchius orthonotus, N. furzeri, N. kadleci, and N. pienaari) across a gradient of aridity in Mozambique. Seventeen parasite taxa were recorded, with trematode larval stages (metacercariae) being the most abundant taxa. The parasites recorded were both allogenic (life cycle includes non‐aquatic host; predominantly trematodes) and autogenic (cycling only in aquatic hosts; nematodes). The parasite abundance was highest in climatic regions with intermediate aridity, while parasite diversity was associated with local environmental characteristics and positively correlated with fish species diversity and the amount of aquatic vegetation. Our results suggest that parasite communities of sympatric Nothobranchius species are similar and dominated by the larval stages of generalist parasites. Therefore, Nothobranchius serve as important intermediate or paratenic hosts of parasites, with piscivorous birds and predatory fish being their most likely definitive hosts.     

Fifty years later: trophic ecology and niche overlap of a native and non-indigenous fish species in the western basin of Lake Erie

Since the introduction of white perch (Morone americana) into Lake Erie over 50 years ago, the population size of native yellow perch (Perca flavescens) has decreased up to 79 % and significant changes to the ecosystem have occurred. We examined long-term population estimates and used stable isotopes of carbon (δ ¹³C) and nitrogen (δ ¹⁵N) paired with stomach content analysis to quantify the trophic ecology and niche overlap of adult yellow perch and white perch in the western basin of Lake Erie. We found that changes in yellow perch abundance since 1979 appeared to be better correlated with changes in fishery exploitation rates than with food competition effects from white perch. At the time of this study, yellow perch were found to have higher δ ¹³C values, indicating greater utilization of benthic food resources than white perch, and white perch occupied higher trophic positions based on δ ¹⁵N. The diets of both species varied spatially and seasonally based on stable isotopes and stomach contents, likely driven by changes in prey abundance. Comparison of niche widths using stable isotope population metrics and Schoener diet similarity index suggested a low to moderate degree of niche overlap between species. Isotopic niches of white perch were generally larger than those of yellow perch demonstrating broader resource utilization by this non-indigenous species. We submit that isotopic niche overlap comparisons are more appropriate for studies seeking to understand interactions among populations over course temporal scales, while diet overlap indices, such as the Schoener index provide a means to study fine-scale interactions such as ontogenetic and seasonal diet shifts.     

Trophic ecology of three stingrays (Myliobatoidei: Dasyatidae) off the Brazilian north-eastern coast: Habitat use and resource partitioning

Understanding the ecological role of species with overlapping distributions is central to inform ecosystem management. Here we describe the diet, trophic level and habitat use of three sympatric stingrays, Hypanus guttatus, H. marianae and H. berthalutzae, through combined stomach content and stable isotope (δ¹³C and δ¹⁵N) analyses. Our integrated approach revealed that H. guttatus is a mesopredator that feeds on a diverse diet of benthic and epibenthic marine and estuarine organisms, principally bivalve molluscs, Alpheus shrimp and teleost fishes. Isotopic data supported movement of this species between marine and estuarine environments. H. berthalutzae is also a marine generalist feeder, but feeds primarily on teleost fishes and cephalopods, and consequently occupies a higher trophic level. In contrast, H. marianae is a mesopredator specialized on shrimps and polychaetas occurring only in the marine environment and occupying a low niche breadth. While niche overlap occurred, the three stingrays utilized the same prey resources at different rates and occupied distinct trophic niches, potentially limiting competition for resources and promoting coexistence. These combined data demonstrate that these three mesopredators perform different ecological roles in the ecosystems they occupy, limiting functional redundancy.     

Seasonal variation in terrestrial resource subsidies influences trophic niche width and overlap in two aquatic snake species: a stable isotope approach

Quantifying diet is essential for understanding the functional role of species with regard to energy processing, transfer, and storage within ecosystems. Recently, variance structure in the stable isotope composition of consumer tissues has been touted as a robust tool for quantifying trophic niche width, a task that has previously proven difficult due to bias in direct dietary analyses and difficulties in integrating diet composition over time. We used carbon and nitrogen stable isotope analyses to examine trophic niche width of two sympatric aquatic snakes, banded watersnakes Nerodia fasciata and black swamp snakes Seminatrix pygaea inhabiting an isolated wetland where seasonal migrations of amphibian prey cause dramatic shifts in resource availability. Specifically, we characterized snake and prey isotope compositions through time, space, and ontogeny and examined isotope values in relation to prey availability and snake diets assessed by gut content analysis. We determined that prey cluster into functional groups based on similarity of isotopic composition and seasonal availability. Isotope variance structure indicated that the trophic niche width of the banded watersnake was broader (more generalist) than that of the black swamp snake. Banded watersnakes also exhibited seasonal variation in isotope composition, suggesting seasonal diet shifts that track amphibian prey availability. Conversely, black swamp snakes exhibited little seasonal variation but displayed strong ontogenetic shifts in carbon and nitrogen isotope composition that closely paralleled ontogenetic shifts in their primary prey, paedomorphic mole salamanders Ambystoma talpoideum. Although niche dimensions are often treated as static, our results demonstrate that seasonal shifts in niche dimensions can lead to changes in niche overlap between sympatric species. Such short‐term fluctuations in niche overlap can influence competitive interactions and consequently the composition and dynamics of communities and ecosystems.     

Population-level metrics of trophic structure based on stable isotopes and their application to invasion ecology

Biological invasions are a significant driver of human-induced global change and many ecosystems sustain sympatric invaders. Interactions occurring among these invaders have important implications for ecosystem structure and functioning, yet they are poorly understood. Here we apply newly developed metrics derived from stable isotope data to provide quantitative measures of trophic diversity within populations or species. We then use these to test the hypothesis that sympatric invaders belonging to the same functional feeding group occupy a smaller isotopic niche than their allopatric counterparts. Two introduced, globally important, benthic omnivores, Louisiana swamp crayfish (Procambarus clarkii) and carp (Cyprinus carpio), are sympatric in Lake Naivasha, Kenya. We applied our metrics to an 8-year data set encompassing the establishment of carp in the lake. We found a strong asymmetric interaction between the two invasive populations, as indicated by inverse correlations between carp abundance and measures of crayfish trophic diversity. Lack of isotopic niche overlap between carp and crayfish in the majority of years indicated a predominantly indirect interaction. We suggest that carp-induced habitat alteration reduced the diversity of crayfish prey, resulting in a reduction in the dietary niche of crayfish. Stable isotopes provide an integrated signal of diet over space and time, offering an appropriate scale for the study of population niches, but few isotope studies have retained the often insightful information revealed by variability among individuals in isotope values. Our population metrics incorporate such variation, are robust to the vagaries of sample size and are a useful additional tool to reveal subtle dietary interactions among species. Although we have demonstrated their applicability specifically using a detailed temporal dataset of species invasion in a lake, they have a wide array of potential ecological applications.     

Otoliths of Five Extant Species of the Annual Killifish Nothobranchius from the East African Savannah

This study presents, for the first time, a comprehensive dataset that documents the range of inter- and intraspecific otolith variation in aplocheiloid killifish, based on a total of 86 individuals representing five extant species of Nothobranchius PETERS, 1868, from East Africa: the sympatric pairs N. rubripinnis SEEGERS, 1986 and N. ruudwildekampi COSTA, 2009 (Eastern Tanzania), and N. orthonotus (PETERS, 1844) and N. furzeri JUBB, 1971 (Southern Mozambique), and two isolated populations of N. korthausae MEINKEN, 1973 (Eastern Tanzania). Otolith characters were analysed based on SEM images, and otolith morphometry was conducted using uni- and multivariate statistics. Two ancient clades of probably Early to Middle Miocene age in eastern Tanzania and southern Mozambique can be recognized based on otolith morphologies, which is consistent with previous work based on molecular data. The distinctive sulcus morphologies in the otoliths of sympatric species may be linked to species-specific hearing capabilities, perhaps constituting a case of character displacement in an area of secondary sympatry. The otoliths of the studied species of Nothobranchius are diagnostic at the species level, even in the case of closely related species diagnosable otherwise only by minor differences in coloration. The two populations of N. korthausae also displayed some differences in their otolith characters. The new data may facilitate future recognition of fossil species of Nothobranchius. As no fossil remains of extant aplocheiloid killifishes have yet been described, the discovery of fossil otoliths of Nothobranchius would significantly advance understanding of the evolutionary history of this interesting group of fishes.     

Dietary niche partitioning in sympatric gadid species in coastal Newfoundland: evidence from stomachs and C-N isotopes

The feeding habits of co-occurring gadid species Atlantic cod (Gadus morhua) and Greenland cod (Gadus ogac) in coastal Newfoundland waters, examined using stable isotope (δ ¹³C and δ ¹⁵N) and stomach content analysis, indicated little dietary niche overlap and interspecific competition for food resources despite similar trophic levels. Both species consumed a variety of invertebrates and fish but showed a preference for different prey items. Polychaetes, fish and small crustaceans dominated G. ogac stomach contents while small crustaceans, in particular hyperiid amphipods and fish, dominated those of G. morhua. In general, G. morhua consumed more pelagic prey and had a significantly more pelagic (more negative) δ ¹³C signature while G. ogac consumed primarily benthic prey and had a more benthic (more positive) δ ¹³C signature. δ ¹⁵N levels were similar in these species suggesting similar trophic positions, with levels increasing with fish length in both species. Dietary overlap was not significant in both stomach and stable isotope analyses. We conclude that interspecific competition for food is low between G. ogac and G. morhua and is unlikely to be a factor in the slow rebuilding of Atlantic cod in this region.     

Comparative feeding ecology of invasive Ponto-Caspian gobies

Invasions of Ponto-Caspian gobiid fishes are suspected to cause regime shifts in freshwater ecosystems. This study compared the trophic niche differentiations of Neogobius melanostomus and Ponticola kessleri in the upper Danube River using stable isotope analyses (δ¹³C and δ¹⁵N), gut content analyses and morphometric analyses of the digestive tract. Both species were identified as predacious omnivores with high dietary overlap and a generalistic feeding strategy. Amphipods (especially invasive Dikerogammarus spp.) contributed 2/3 to the index of food importance. δ¹⁵N-signatures of N. melanostomus revealed an ontogenetic diet shift and significantly exceeded those in P. kessleri by ~1.5‰, indicating a niche separation of half a trophic level. P. kessleri had shorter uncoiled intestinal tracts than N. melanostomus, indicating a narrower niche and adaptation to animal food. Trophic niches in both species expanded during the growth period with increasing intraguild predation and cannibalism in P. kessleri and increasing molluscivory in N. melanostomus. P. kessleri showed a higher degree of specialization and more stable feeding patterns across seasons, whereas N. melanostomus adapted its diet according to the natural prey availability. The feeding patterns of both species observed in the upper Danube River strongly differ from those in their native ranges, underlining their great plasticity. Both goby species consumed mainly other non-native species (~92% of gut contents) and seemed to benefit from previous invasions of prey species like Dikerogammarus villosus. The invasive success of gobies and their prey mirror fundamental ecological changes in large European freshwater ecosystems.     

The trophic structure of bark-living oribatid mite communities analysed with stable isotopes (15N, 13C) indicates strong niche differentiation

The aim of the present study was to identify food sources of bark-living oribatid mites to investigate if trophic niche differentiation contributes to the diversity of bark living Oribatida. We measured the natural variation in stable isotope ratios (¹⁵N/¹⁴N, ¹³C/¹²C) in oribatid mites from the bark of oak (Quercus robur), beech (Fagus sylvatica), spruce (Picea abies) and pine (Pinus sylvestris) trees and their potential food sources, i.e., the covering vegetation of the bark (bryophytes, lichens, algae, fungi). As a baseline for calibration the stable isotope signatures of the bark of the four tree species were measured and set to zero. Oribatid mite stable isotope ratios spanned over a range of about 13 δ units for ¹⁵N and about 7 δ units for ¹³C suggesting that they span over about three trophic levels. Different stable isotope signatures indicate that bark living oribatid mites feed on different food sources, i.e., occupy distinct trophic niches. After calibration stable isotope signatures of respective oribatid mite species of the four tree species were similar indicating close association of oribatid mites with the corticolous cover as food source. Overall, the results support the hypothesis that trophic niche differentiation of bark living oribatid mites contributes to the high diversity of the group.     

Questioning assumptions of trophic behavior in a broadly ranging marine predator guild

We evaluated whether existing assumptions regarding the trophic ecology of a poorly‐studied predator guild, northwest (NW) Atlantic skates (family: Rajidae), were supported across broad geographic scales. Four hypotheses were tested using carbon (δ¹³C) and nitrogen (δ¹⁵N) stable isotope values as a proxy for foraging behavior: 1) species exhibit ontogenetic shifts in habitat and thus display a shift in ¹³C with differential use of the continental shelf; 2) species exhibit ontogenetic prey shifts (i.e. from smaller to larger prey items) and become enriched in ¹⁵N; 3) individuals acquire energy from spatially confined local resource pools and exhibit limited displacement; and 4) species exhibit similarly sized and highly overlapping trophic niches. We found some evidence for ontogenetic shifts in habitat‐use (δ¹³C) for thorny and little skate and diet (δ¹⁵N) of thorny and winter skate and hypothesize that individuals exhibit gradual trophic niche transition, especially in δ¹⁵N space, rather than a clear and distinct shift in diet throughout ontogeny. Spatial isoscapes generated for little, thorny, and winter skate highlighted distinct spatial patterns in isotopic composition across the coastal shelf. For little and thorny skate, patterns mimicked expected spatial variability in the isotopic composition of phytoplankton/POM, suggesting limited displacement and utilization of spatially confined resource pools. Winter skate, however, exhibited a much narrower range of δ¹³C and δ¹⁵N values, suggesting individuals may use resources from a more confined latitudinal range. Although high total trophic niche overlap was observed between some species (e.g. little and thorny skate), sympatric species (e.g. little and winter skate) exhibited a degree of trophic niche separation. These findings offer new insight into the trophic dynamics of a poorly‐studied, vulnerable group of predators, and highlight a need to re‐examine assumptions pertaining to aspects of their ecology.     

Trophic niches and feeding relationships of shorebirds in southern Brazil

Niche theory predicts that sympatric species should differ in some ecological characteristic, to allow co-existence and reduce competition for key resources. Food is critical on wintering grounds and stopover areas for migratory species that need to accumulate reserves in order to complete their migration. Wetlands of the Rio Grande do Sul coastal plain, in southern Brazil, host several species of shorebirds with similar morphology, foraging methods and diet. When these species are in sympatry, some trophic niche overlap is expected. Diets and trophic niches of migratory and resident shorebirds were investigated during the austral summer on Torotama Island, Lagoa dos Patos Estuary, Brazil. Complementary methods were used to determine the trophic ecology of three shorebird species; diet was determined through analysis of feces and food samples, using stable isotopes of carbon and nitrogen. The local invertebrate community was sampled to determine potential prey and ascertain feeding preferences of birds. Coleoptera was the most abundant taxon in the feces of all shorebirds. Trophic niche overlap in the diets was high, with the widest trophic niche found for the buff-breasted sandpiper Calidris subruficollis. Isotopic mixing models indicated differences in the main food sources of shorebirds. The isotopic niche breadth was widest for the American golden-plover Pluvialis dominica. These species, as well as the resident southern lapwing Vanellus chilensis, consumed some prey in higher proportions over others, although they had generalist diets. Migratory species with generalist habits benefit from heterogeneous environments such as floodplains during the non-breeding season.     

Different groups of ground-dwelling spiders share similar trophic niches in temperate forests

1. Generalistic interactions between predator and prey may vary with ecosystem type, predator traits, and prey traits, but the interplay of these factors has not been assessed in ground food webs.
2. We investigated trophic interactions of ground-dwelling spiders across eight forests in European Russia associated with body size, hunting strategy, microhabitat specialization, potential prey type, potential prey population density, and forest type (coniferous vs. broadleaved). We analyzed 128 individual spiders, including juveniles, all identified to the family level with two complementary methods: molecular gut content analysis, and stable isotope analysis of carbon and nitrogen.
3. The results suggest that feeding frequency of spiders is affected by predator body size and by selection of certain prey type. Stable isotope analysis showed similar trophic niches among spider families, varying moderately with forest type. Larger spiders had higher Δ¹³C values than smaller ones, but similar Δ¹⁵N values, suggesting that different size classes of spiders belong to different food chains. Results based on stable isotope and molecular gut content analyses were weakly linked, indicating them targeting different trophic niche dimensions.
4. At least for the group-level interactions, family identity and hunting strategy of predator has little predictive power while predator body size and prey traits affected trophic niche dimensions calling for future studies in this direction. Large spiders feed more and rely on different basal resources than small spiders, suggesting that including small species and juveniles provides a more comprehensive picture of food web organization.

     

Temporal variation in trophic relationships among three congeneric penguin species breeding in sympatry

Penguins are a monophyletic group in which many species are found breeding sympatrically, raising questions regarding how these species coexist successfully. Here, the isotopic niche of three sympatric pygoscelid penguin species was investigated at Powell Island, South Orkney Islands, during two breeding seasons (austral summers 2013–2014 and 2015–2016). Measurements of carbon (δ¹³C) and nitrogen (δ¹⁵N) stable isotope ratios were obtained from blood (adults) or feather (chicks) samples collected from Adélie Pygoscelis adeliae, chinstrap P. antarctica, and gentoo P. papua penguins. Isotopic niche regions (a proxy for the realized trophic niches) were computed to provide estimates of the trophic niche width of the studied species during the breeding season. The isotopic niche regions of adults of all three species were similar, but gentoo chicks had noticeably wider isotopic niches than the chicks of the other two species. Moderate to strong overlap in isotopic niche among species was found during each breeding season and for both age groups, suggesting that the potential for competition for shared food sources was similar during the two study years, although the actual level of competition could not be determined owing to the lack of data on resource abundance. Clear interannual shifts in isotopic niche were seen in all three species, though of lower amplitude for adult chinstrap penguins. These shifts were due to variation in carbon, but not nitrogen, isotopic ratios, which could indicate either a change in isotopic signature of their prey or a switch to an alternative food web. The main conclusions of this study are that (1) there is a partial overlap in the isotopic niches of these three congeneric species and that (2) they responded similarly to changes that likely occurred at the base of their food chain between the 2 years of the study.     

Trophic niche segregation allows range‐extending coral reef fishes to co‐exist with temperate species under climate change

Changing climate is forcing many terrestrial and marine species to extend their ranges poleward to stay within the bounds of their thermal tolerances. However, when such species enter higher latitude ecosystems, they engage in novel interactions with local species, such as altered predator–prey dynamics and competition for food. Here, we evaluate the trophic overlap between range‐extending and local fish species along the east coast of temperate Australia, a hotspot for ocean warming and species range extensions. Stable isotope ratios (δ¹⁵N and δ¹³C) of muscle tissue and stomach content analysis were used to quantify overlap of trophic niche space between vagrant tropical and local temperate fish communities along a 730 km (6°) latitudinal gradient. Our study shows that in recipient temperate ecosystems, sympatric tropical and temperate species do not overlap significantly in their diet—even though they forage on broadly similar prey groups—and are therefore unlikely to compete for trophic niche space. The tropical and temperate species we studied, which are commonly found in shallow‐water coastal environments, exhibited moderately broad niche breadths and local‐scale dietary plasticity, indicating trophic generalism. We posit that because these species are generalists, they can co‐exist under current climate change, facilitating the existence of novel community structures.     

Trophic response to ecological conditions of habitats: Evidence from trophic variability of freshwater fish

1. To adapt to ecological and environmental conditions, species can change their ecological niche (e.g., interactions among species) and function (e.g., prey‐predation, diet competition, and habitat segregation) at the species and guild levels. Stable isotope analysis of bulk carbon and nitrogen of organisms has conventionally been used to evaluate such adaptabilities in the scenopoetic and bionomic views as the isotopic niche width.
2. Compound‐specific stable isotope analysis (CSIA) of nitrogen within amino acids provides trophic information without any disruption of scenopoetic views in the isotope ratios, unlike conventional bulk isotope analysis provides both information and therefore frequently hinders its usefulness for trophic information.
3. We performed CSIA of amino acids to understand the trophic variability of the pike gudgeon Pseudogobio esocinus and largemouth bass Micropterus salmoides as representative specialist and generalist fish species, respectively, from 16 ecologically variable habitats in the four major rivers of Korea.
4. There was little variation (1σ) in the trophic position (TP) among habitats for P. esocinus (± 0.2); however, there was considerably large variation for M. salmoides (± 0.6). The TP of M. salmoides was negatively correlated with the benthic invertebrate indices of the habitats, whereas the TP of P. esocinus showed no significant correlation with any indices. Thus, these two representative fish species have different trophic responses to ecological conditions, which is related to known differences in the trophic niche between specialists (i.e., small niche width) and generalists (i.e., large niche width).
5. Over the past four decades, the conventional bulk isotope analysis has not been capable of deconvoluting “scenopoetic” and “bionomic” information. However, in the present study, we demonstrated that the CSIA of amino acids could isolate trophic niches from the traditional ecological niche composed of trophic and habitat information and evaluated how biological and ecological indices influence the trophic response of specialists and generalists.

     

Evolutionary convergence in Neotropical cichlids and Nearctic centrarchids: evidence from morphology,diet, and stable isotope analysis

Despite divergent evolutionary histories, Neotropical cichlids (Cichlidae) and Nearctic sunfishes (Centrarchidae) appear to have similar functional morphotypes and occupy similar ecological niches. We applied an integrative approach analyzing morphological traits, stomach contents, and stable isotope ratios (δ¹³C, δ¹⁵N) to investigate whether local assemblages of cichlids (Venezuela, Peru) and centrarchids (Texas) reveal one‐to‐one patterns of morphological and ecological convergence. Multivariate ordinations performed on diet and morphology datasets identified a broad overlap between cichlid and centrarchid assemblages. The functional morphology of the two groups has diversified in a convergent manner within the confines of ram‐suction modes of prey ingestion. Both groups had the same set of ecomorph types that corresponded to the same trophic niches, including substrate‐sifting invertivores, epibenthic invertebrate gleaners, and piscivores; the one exception was a molluscivorous sunfish, comprising a niche that was not represented in the two cichlid assemblages. Estimates of trophic positions based on stable isotope analysis revealed convergent vertical trophic structure; with few exceptions, fishes with similar morphologies had similar trophic positions. Large‐bodied piscivores had highest trophic positions, whereas small and medium‐bodied generalists and invertivores had low to intermediate trophic positions. Consistent patterns of ecomorphological convergence in these two perciform groups provide strong evidence for adaptation involving constrains in functional morphology associated with feeding. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2013, 109 , 146–164.     

High-throughput sequencing reveals dietary segregation in Malaysian babblers

The coexistence of numerous species within a community results from how those species use available resources. Babblers are one of the major groups of Malaysian insectivorous birds, which frequently forage in dense vegetation cover and have a high level of sympatry. Therefore, examining the diet, prey selection, and niche segregation of babblers can be challenging. In this study, we used high-throughput sequencing to investigate potential dietary overlap or segregation among 10 babbler species of the 4 genera of the family Pellorneidae and Timaliidae: Pellorneum, Malacopteron, Stachyris, and Cyanoderma in central peninsular Malaysia. We tested the hypothesis that trophically similar species may differ in resource use to avoid competitive exclusion. We identified 81 distinct arthropod taxa from fecal samples, belonging to 71 families representing 13 orders, which were predominantly from 16 dipteran, 13 lepidopteran, and 10 coleopteran families. Of all the prey taxa consumed, 45% were found to be distinct across the 10 babbler species, and ˂35% were shared simultaneously by ≥3 babbler species, indicating minimal dietary overlap. The black-throated babbler Stachyris nigricollis and moustached babbler Malacopteron magnirostre had the most generalist tendencies because they consumed a greater variety of prey taxa. Small dietary overlap values (Ojk) and a relatively wide range of food resources suggest that dietary segregation occurred among the studied babblers. The great diversity of prey consumed revealed the presence of dietary flexibility among the sympatric insectivorous birds, thus reducing any active dietary competition and facilitating the coexistence through niche partitioning.     

Stable-isotope analysis of a deep-sea benthic-fish assemblage: evidence of an enriched benthic food web

In this study, fishes and invertebrates collected from the continental slope (1000 m) of the eastern North Pacific Ocean were analysed using stable-isotope analysis (SIA). Resulting trophic positions (T(P) ) were compared to known diets and habitats from the literature. Dual isotope plots indicated that most species groups (invertebrates and fishes) sorted as expected along the carbon and nitrogen axes, with less intraspecific variability than interspecific variability. Results also indicated an isotopically distinct benthic and pelagic food web, as the benthic food web was more enriched in both nitrogen and carbon isotopes. Trophic positions from SIA supported this finding, resulting in the assignment of fishes to different trophic positions from those expected based on published dietary information. These differences can be explained largely by the habitat of the prey and the percentage of the diet that was scavenged. A mixing model estimated dietary contributions of prey similar to those of the known diet of Bathyraja trachura from stomach-content analysis (SCA). Linear regressions indicated that trophic positions calculated from SIA and SCA, when plotted against B. trachura total length for 32 individuals, exhibited similar variation and patterns. Only the T(P) from SCA yielded significant results (stomach content: P < 0·05, stable isotope: P > 0·05).