Trophic Partitioning Research Articles

Dietary tendencies of the Early Jurassic pterosaurs Campylognathoides Strand, 1928, and Dorygnathus Wagner, 1860, with additional evidence for teuthophagy in Pterosauria

ABSTRACT The diets and feeding strategies of pterosaurs remain a poorly known although speculatively debated topic in vertebrate paleontology. Fossilized gut contents, which offer a crucial direct line of evidence to help decipher these elusive questions, are only known from a handful of pterosaur specimens in a few notable fossil Lagerstätten, such as the Solnhofen Limestone of Bavaria. Although extremely rare, pterosaurs can be exceptionally well preserved in the Lower Jurassic (Toarcian) Posidonia shale of Baden–Württemberg but, until now, none have been reported with identifiable gut contents. Here, we describe fossilized gut contents in two Posidonia Shale pterosaurs: Dorygnathus banthensis (Rhamphorhynchidae) and Campylognathoides zitteli (Campylognathoididae). Dorygnathus is shown to be piscivorous as indicated by the inclusion of the small teleost Leptolepis sp. preserved inside of the abdominal cavity. The gastrointestinal tract of Campylognathoides preserves associated accumulations of belemnoid hooklets referrable to Clarkeiteuthis conocauda and thereby demonstrating a teuthophagous diet. These findings represent the first convincing evidence for belemnoids contributing to the diet of a pterosaur and hint at a possible nocturnal hunting behavior for Campylognathoides. Previous hypotheses regarding dietary trophic partitioning based on differentiating skull anatomy in Posidonia Shale pterosaurs are supported.

Trophic Partitioning among Three Mesopredatory Shark Species Inhabiting the Northwestern Adriatic Sea

While the general diet of Mediterranean elasmobranchs has been widely studied, little is known about food partitioning and competition among sympatric species, despite these being important forces structuring marine communities. Using stomach content and stable isotope analyses, we investigated diet and trophic levels and evaluated the diet overlap and partitioning of Scyliorhinus canicula, Mustelus mustelus, and M. punctulatus in the northwestern Adriatic Sea. These shark species were confirmed as opportunistic mesopredators, but significant differences in their diets emerged. The two bentho-demersal Mustelus species had a larger trophic overlap with S. canicula than between each other. Given the pronounced morphological similarity of these two Mustelus species, this is likely a strategy to limit competition. The strictly benthic S. canicula showed a more varied diet compared to the other species. Stable isotope analysis highlighted that despite the smaller size and overlapping diets, S. canicula occupied a slightly higher trophic level. A better characterization of the trophic role of these species in the food web of the basin can be obtained from these data. At an ecosystem level, this information is essential to evaluate the possible consequences of the decline or recovery of the population of these exploited species.

A diverse assemblage of Ptychodus species (Elasmobranchii: Ptychodontidae) from the Upper Cretaceous of Ukraine, with comments on possible diversification drivers during the Cenomanian

New isolated teeth from the Upper Cretaceous of Ukraine and belonging to the extinct durophagous shark Ptychodus are described here. The taxonomic identification of the examined material reveals a quite diverse Cenomanian shark fauna which comprised both cuspidate and un-cuspidate species of Ptychodus from the coastal areas at the north-western margin of the Ukrainian Massif. In addition, P. latissimus from the Turonian of Ukraine is reported here for the first time. The revision of the Ukrainian record of Ptychodus revealed that most specimens described here are the oldest so far known from this part of the European Peri-Tethys. Moreover, the present study highlights the co-occurrence of cuspidate and un-cuspidate Ptychodus and a variety of shelled macroinvertebrates, which inhabited coastal and offshore areas of the European epicontinental seas during the Late Cretaceous. The availability of different prey items is proposed here as one of the possible drivers, in addition to abiotic environmental factors, for the diversification of shark tooth morphologies, and possible trophic partitioning between cuspidate and un-cuspidate species of the genus Ptychodus.

Trophic partitioning among seasonally resident predators in a temperate estuary

Many migratory coastal shark species enter temperate estuaries seasonally, tracking suitable environmental conditions (i.e. temperature) and food resources. Understanding the functional role that migratory sharks play in coastal food webs depends on information regarding the distinctness among predators’ trophic ecology. We examined the trophic ecology of 4 species of coastal sharks (Atlantic sharpnose, n = 22; bonnethead, n = 29; blacktip, n = 8; blacknose, n = 28) that migrate into temperate coastal ecosystems of the northwest Atlantic Ocean during the summer. We quantified their trophic relationships using bulk stable isotope ratios (δ13C, δ15N, and δ34S) measured in 2 tissue types representing long-term (red blood cells; 8-10 mo) and short-term (blood plasma; 10-13 wk) metabolic turnover. The primary carbon sources for the 4 shark species, determined via stable isotope mixing models, were consistently phytoplankton (mean ± SD: 65.8 ± 4.8%) and microphytobenthos (18.6 ± 5.4%), regardless of tissue type. However, interspecific isotopic niche overlap between any 2 species ranged widely (0-92%). The niche space occupied exclusively by one species also varied considerably but was lowest for blacktips (<20%) and highest for bonnetheads (>90%). Isotopic niche size estimated using short-term tissues, was substantially larger for 3 of the 4 species (Atlantic sharpnose, 41% increase; blacknose, 140%; blacktips, 159%) than long-term tissues. These data suggest species-specific trophic redundancy and increasing overlap in the summer months, indicated by larger isotopic niches during estuarine residency. As coastal habitats become increasingly altered, understanding the functional diversity of predators is vital for the prediction and assessment of resulting ecosystem-level change.

Climate tracking by freshwater fishes suggests that fish diversity in temperate lakes may be increasingly threatened by climate warming

AbstractAimMany freshwater fishes are migrating poleward to more thermally suitable habitats in response to warming climates. In this study, we aimed to identify which freshwater fishes are most sensitive to climatic changes and asked: (i) how fast are lakes warming? (ii) how fast are fishes moving? and (iii) are freshwater fishes tracking climate?LocationOntario, Canada.MethodsWe assembled a database containing time series data on climate and species occurrence data from 10,732 lakes between 1986 and 2017. We calculated the rate of lake warming and climate velocity for these lakes. Climate velocities were compared with biotic velocities, specifically the rate at which the northernmost extent of each species shifted north.ResultsLakes in Ontario warmed by 0.2°C decade−1 on average, at a climate velocity of 9.4 km decade−1 between 1986 and 2017. In response, some freshwater fishes have shifted their northern range boundaries with considerable interspecific variation ranging from species moving southwards at a rate of −58.9 km decade−1 to species ranges moving northwards at a rate of 83.6 km decade−1 over the same time period. More freshwater fish species are moving into northern lakes in Ontario than those being lost. Generally, predators are moving their range edges northwards, whereas prey fishes are being lost from northern lakes.Main ConclusionsThe concurrent loss of cooler refugia, combined with antagonistic competitive and predatory interactions with the range expanding species, has resulted in many commercially important predators moving their range edges northwards, whereas prey species have contracted their northern range edge boundaries. Trophic partitioning of range shifts highlights a previously undocumented observation of the loss of freshwater fishes from lower trophic levels in response to climate‐driven migrations.

Interspecific and intraspecific comparison of the isotopic niche of shrimps targets of fishing in south-eastern Brazil

AbstractThe study compares the isotopic niche (δ13C–δ15N) of three species of penaeid shrimps (Xiphopenaeus kroyeri, Artemesia longinaris and Litopenaeus schmitti) that are targets of fishing in south-eastern Brazil. The two hypotheses raised are based on the niche theory, in which the coexistence between organisms that have similar dietary demands is possible due to trophic partitioning: (i) shrimp species that share the habitat have segregated isotopic niches; and (ii) stages of maturity and genders vary with the trophic habitat (δ13C) and/or trophic position (δ15N). In multispecific fishing grounds, the isotopic niches of the shrimp species were segregated or had low overlap, indicating trophic partitioning. The intraspecific comparison of δ13C and δ15N showed a similar trend in all species. For δ13C, the values were more enriched in adult individuals than in juveniles, but similar between males and females. For δ15N, adult individuals also had more enriched values, and males were more enriched than females. The results confirm the hypotheses raised, and the assumptions of niche theory apply to these penaeid shrimps.

Trophic ecology of four species of emperor fish (Lethrinus) in the Gulf of Mannar along the Indian southeast coast

This study presents the trophic ecology and resource partitioning among four species of emperor fishes (Lethrinus lentjan, L.microdon, L. nebulosus and L.olivaceus) in the Gulf of Mannar, based on a year-round study conducted in 2019. All of them are demersal feeders with strong jaws, having certain differences in their body shape and dentition. The diet content analyses revealed that slow-moving benthic invertebrates such as molluscs, crustaceans, and echinoderms were the major diet components of L.lentjan and L. nebulosus, whereas, L.microdon and L.olivaceus predominantly consumed fast-moving prey that included nektons and other invertebrate taxa. The dominant prey components in the diet of smaller fishes are highly contrary to the adults, as larger fishes cover wider feeding grounds and choose among a broader category of prey, which is significant for greater nutritional input. The slender body shape, jaw structure, and foraging behaviour enable larger fish to consume a far greater proportion of nekton. The index of relative importance (IRI %) showed that bivalves, brachyurans, and carideans were the most prevalent food items in the diets of all size classes. TROPH values estimated by species and size groups indicate that L.microdon (3.71) occupies the highest trophic position, followed by L.olivaceus (3.68), L.lentjan (3.45), and L. nebulosus (3.37). The variety and frequency of prey components in L.microdon and L.olivaceus substantiate the distinctive feeding nature of piscivory with an ontogenic diet shift. The observed trophic partitioning among the four Lethrinus species in the Gulf of Mannar can be attributed to vertical habitat partitioning and their distinctive morphological characteristics.

Sr/Ca and Ba/Ca ratios support trophic partitioning within a Silurian conodont community from Gotland, Sweden

AbstractConodonts were a highly diverse and abundant vertebrate group whose fossils are found in marine Paleozoic and Triassic strata around the world. They inhabited environments ranging from lagoons to open oceans and are represented by a wide variety of dental morphologies. Conodonts may have filled many different ecological niches and represent a significant proportion of nekton before the Devonian. Despite this, very little is known about trophic ecology of conodonts. While morphological diversity suggests a complex trophic structure within conodont communities, there is little evidence to support dietary niche partitioning among conodonts.We tested the hypothesis that individual conodont taxa occupied different trophic niches, using Sr/Ca and Ba/Ca ratios preserved in the dental elements of assemblages from Silurian strata of Gotland, Sweden. Sr/Ca and Ba/Ca have been shown to vary in vertebrate skeletal tissues depending on trophic positioning, although biological and environmental conditions can affect these ratios. Environmental influences were minimized by examining entire conodont communities from a tropical epeiric sea and by measuring strontium isotope ratios using thermal ionization mass spectrometry in the most metropolitan taxon (Ozarkodina confluens). Composition of white matter, a tissue unique to conodonts, was also analyzed using microprobe analysis, revealing significantly lower Sr concentrations than in surrounding lamellar tissue, suggesting taxon-specific histology should be considered when analyzing conodonts for geochemical data. Excluding taxa with highly variable quantities of white matter, the results show that each taxon preserves different Sr/Ca and Ba/Ca ratios with limited overlap, indicating variation in trophic positioning.

Taxonomic versus ecological prey traits among arthropodophagous bats: implications for surveying trophic partitioning patterns

Abstract Species can coexist spatially and temporally by partitioning the niche space and forming complex assemblages made up of different species that share the prey resource. Chiroptera is the second most species-rich mammalian order and about 75% of bat species feed on arthropods, which makes these bats a good model group for studying complex trophic interactions. Next-generation parallel sequencing techniques allow a detailed analysis of arthropod resource partitioning patterns in bats. However, previous studies have not reached a consensus on the concordance between diet composition, habitat use, and segregation of trophic resources in bats. We analyzed diet composition in terms of taxonomy of the insect prey, and the prey characteristics. Feces of 16 bat species were examined in the Mexican Neotropics. We carried out a SIMPER (similarity percentage) test, nonmetric multidimensional scaling, and principal component analyses to identify general segregation patterns of trophic resources in relation to the habitat-use guild of bats and computed Pianka’s niche overlap index between species and Levin’s index to estimate the niche width of each species. Bats from the same locality tend to partition their diet, with a niche overlap ranging between 0.5 and 0.8. The highest values were found between species with different foraging behaviors. We suggest that future bat diet studies should incorporate the ecological and taxonomic information of arthropod prey to better understand the trophic interactions with bats.

Feeding ecology, trophic interaction and resource partitioning among four omnivorous finfish species of a tropical Estuary

A crucial aspect of sustainable resource management is understanding the trophic interactions amongst fish in the estuarine ecosystem. The goal of this study was to look into the food preferences, feeding strategies, trophic partitioning, as well as dietary overlap among four omnivorous species that live in the Cochin Estuary: Mugil cephalus (n = 73), Planiliza parsia (n = 35), Planiliza planiceps (n = 65) and Chanos chanos (n = 55) through the analyses of gut-content. Index of relative importance demonstrated that prey items in Mugil cephalus and Planiliza planiceps guts were dominated by Bacillariophyceae whereas in Planiliza parsia and Chanos chanos guts were dominated by Myxophyceae. The highest diet value (7.5) was recorded in Chanos chanos, while the lowest was recorded in Mugil cephalus (5.69). The highest niche breadth value (0.77) was recorded in Planiliza planiceps while the lowest value was recorded in Planiliza parsia (0.52). Pianka's overlap, evaluated with the help of null models structured by Ecosim 7.0, showed remarkable niche overlap between Mugil cephalus and Planiliza planiceps (0–0.92, P < 0.001), between Planiliza planiceps and Planiliza parsia ( 0–0.77, P < 0.05) and between Mugil cephalus and Planiliza parsia ( 0–0.7, P < 0.05). The fish's trophic niche width, along with prey-specific abundance confirmed that they are generalist feeders. The present results differed from the general hypothesis related to the omnivorous species and concluded that these four omnivorous species live in the same niche zones of the Cochin Estuary with no interspecific conflict.

Feeding ecology has shaped the evolution of modern sharks

Sharks are iconic predators in today's oceans, yet their modern diversity has ancient origins. In particular, present hypotheses suggest that a combination of mass extinction, global climate change, and competition has regulated the community structure of dominant mackerel (Lamniformes) and ground (Carcharhiniformes) sharks over the last 66 million years. However, while these scenarios advocate an interplay of major abiotic and biotic events, the precise drivers remain obscure. Here, we focus on the role of feeding ecology using a geometric morphometric analysis of 3,837 fossil and extant shark teeth. Our results reveal that morphological segregation rather than competition has characterized lamniform and carcharhiniform evolution. Moreover, although lamniforms suffered a long-term disparity decline potentially linked to dietary "specialization," their recent disparity rivals that of "generalist" carcharhiniforms. We further confirm that low eustatic sea levels impacted lamniform disparity across the end-Cretaceous mass extinction. Adaptations to changing prey availability and the proliferation of coral reef habitats during the Paleogene also likely facilitated carcharhiniform dispersals and cladogenesis, underpinning their current taxonomic dominance. Ultimately, we posit that trophic partitioning and resource utilization shaped past shark ecology and represent critical determinants for their future species survivorship.

Trophic partitioning and feeding capacity in Permian bryozoan faunas of Gondwana

AbstractBryozoans are epibenthic suspension‐feeders and use their ciliated tentacles to generate feeding currents. Modern bryozoan mouth size limits the size of the particles that can be ingested, and lophophore diameter is correlated with water pumping rates. In fossil bryozoans these soft parts are absent, however mouth and lophophore dimensions can be inferred from preserved skeletons. Gondwanan Permian palaeostomate bryozoans show distinct order‐level trophic partitioning across warm to cold‐water faunas. In diverse warm‐water faunas of southern Thailand, fenestrate bryozoans consumed the smallest food particles, cryptostomes and trepostomes consumed mid‐size particles, and cystoporates consumed the largest, and widest range, of particles. In contrast, in low diversity cold‐water faunas of eastern Australia, where cystoporates and cryptostomes are uncommon, fenestrate bryozoans again consumed the smallest food particles, however the abundant trepostomes had much larger mouths than their warm‐water counterparts and consumed the largest food particles. This variation in mouth size, especially in the trepostomes, suggests that within a regional fauna mouth size is not controlled only by higher level systematics and that sessile benthic organisms are trophically structured to utilize different sized food particles from a suspended food source. Gondwanan Permian palaeostomates had much larger mouth and lophophore sizes than modern stenolaemates (cyclostomes) and are more comparable to gymnolaemate (cheilostome) bryozoans. This suggests that palaeostomates were able to access and consume the same range of food resources as modern gymnolaemate bryozoans, and feed at similar rates, prior to the marine environmental changes at the close of the Palaeozoic.

New method of isotopic analysis: baseline‐standardized isotope vector analysis shows trophic partitioning in loricariids

AbstractStable isotope analyses have refined the study of trophic niche diversity within an ecosystem, yet traditional trophic partitioning methods may not be appropriate to identify variation among groups with similar dietary requirements. By building on vector‐based analyses, we introduce a baseline‐standardized isotopic vector analysis (BaSIVA) to visualize dietary variation while accounting for isotopic discrepancies between locations. To test the effectiveness of our new method, we collected muscle samples from eleven species of Loricarioidea in five assemblages in Northern Peru. Loricarioidea is a large, ecomorphologically diverse superfamily of scraping‐feeding fishes. Most feed on an indistinguishable mix of detritus and algae, but some lineages have specialized diets of wood, seeds, and macroinvertebrates, making them an excellent group to study trophic variation. Isotopic data were collected using mass spectrometric isotope analyses, and communities were standardized by calculating a mean baseline (algae and periphyton) for each location. The entire community was shifted by subtracting the baseline of 15N and 13C from the consumers at each location, which allowed for comparison between assemblages. Incremental differences of 15N and 13C from the baseline were found via vector analysis, and the azimuth and module of each consumer were calculated. Standardization resulted in a significant shift of assemblages within the isotopic biplot, and vector analysis shows three trophic groups primarily described by differences in carbon assimilation. Isotopic variation between species may account for some diversification in jaw shape within the Loricarioidea, but BaSIVA suggests several instances of trophic overlap in different jaw morphologies. Moreover, results from BaSIVA are better able to delineate trophic groups than traditional trophic positioning methods while accounting for variation in basal resources. We suggest a baseline‐standardized vector analysis should be the standard for vector‐based stable isotope analysis in riverine environments with similar baseline resources.

Trophic Partitioning of Cambarus carinirostris, Cambarus robustus, and Faxonius obscurus in Kings Creek, WV by Stable Isotope Analysis

The competitive exclusion principle states that no two species can share the same niche in nature. Partitioning among coexisting species occurs through utilization of various food sources or differences in microhabitat preference. The purpose of this study is to assess potential trophic partitioning between Cambarus carinirostris, Cambarus robustus, and Faxonius obscurus, three species of crayfish present in Kings Creek, Weirton, WV. Analysis and comparison of individual carbon-13 and nitrogen-15 isotope signatures were used to establish organic matter transfer pathways and trophic structures in the ecosystem. Representative trophic groups were sampled, spanning from macro-predators (e.g., smallmouth bass) to primary producers (e.g., macrophytes and algae). All samples were analyzed for carbon-13 and nitrogen-15 by the Stable Isotope Ecology Laboratory at the University of Georgia. Interspecific partitioning within the community was identified. Smallmouth bass were top predators and crayfish were the second highest group. Between the three species of crayfish, interspecific partitioning was suggested. The lowest and highest trophic levels were occupied by C. carinirostris and F. obscurus, respectively. In addition, intraspecific partitioning within each crayfish species suggested that juveniles occupy a lower trophic level than adults, potentially signifying ontogenetic dietary shifts. All analyzed data represent the summer season. Winter results are pending and once available, the two seasons will be compared for any differences in trophic structure.

Ecomorphological divergence and trophic resource partitioning in 15 syntopic Indo-Pacific parrotfishes (Labridae: Scarini)

AbstractAdaptive diversification is a product of both phylogenetic constraint and ecological opportunity. The species-rich parrotfish genera Scarus and Chlorurus display considerable variation in trophic cranial morphology, but these parrotfishes are often described as generalist herbivores. Recent work has suggested that parrotfish partition trophic resources at very fine spatial scales, raising the question of whether interspecific differences in cranial morphology reflect trophic partitioning. We tested this hypothesis by comparing targeted feeding substrata with a previously published dataset of nine cranial morphological traits. We sampled feeding substrata of 15 parrotfish species at Lizard Island, Great Barrier Reef, Australia, by following individuals until focused biting was observed, then extracting a bite core 22 mm in diameter. Three indices were parameterized for each bite core: substratum taphonomy, maximum turf height and cover of crustose coralline algae. Parrotfish species were spread along a single axis of variation in feeding substrata: successional status of the substratum taphonomy and epilithic and endolithic biota. This axis of trophic variation was significantly correlated with cranial morphology, indicating that morphological disparity within this clade is associated with interspecific partitioning of feeding substrata. Phylogenetic signal and phylomorphospace analyses revealed that the evolution of this clade involved a hitherto-unrecognized level of trophic diversification.

Feeding Ecology Has Shaped the Evolution of Modern Sharks

Sharks are iconic predators in today’s oceans, but their modern diversity has ancient origins. In particular, current hypotheses suggest that a combination of mass extinction, global climate change, and competition between dominant Mackerel shark (Lamniformes) and Ground shark (Carcharhiniformes) clades has regulated their community structure over the last 66 million years. However, while these scenarios reflect an interplay of major biotic and abiotic events, the precise drivers remain obscure. Here, we focus on the role of feeding ecology using a morphometric dataset of 3,837 fossil and extant shark teeth. Our results reveal that morphological segregation rather than competitive overlap has characterized modern lamniform and carcharhiniform shark evolution. Moreover, although lamniforms suffered a long-term disparity decline, perhaps due to dietary ‘specialization’, their current disparity rivals that of ‘generalist’ carcharhiniforms. We posit that trophic partitioning and resource availability have shaped shark ecology, and represent critical determinants for future species survivorship.

Reassessment of the Early Triassic trematosaurid temnospondyl Tertrema acuta from the Arctic island of Spitsbergen

ABSTRACT Trematosaurids were globally distributed Early Triassic temnospondyl amphibians characterized by elongate ‘crocodile-like’ skulls. Some of the most famous trematosaurid fossils were discovered on the island of Spitsbergen in the Arctic Svalbard archipelago. Among these, the short-snouted trematosaurine, Tertrema acuta, is one of the few taxa represented by virtually complete cranial remains. Unusually, however, the type specimens comprise only natural molds that were historically used to reconstruct three-dimensional casts. Here, we re-assess these restorations using the original impressions to phylogenetically analyze and re-diagnose the taxon. Unexpectedly, our first-hand scores differ markedly from previous literature-sourced interpretations and yield conflicting tree topologies that nest T. acuta with long-snouted lonchorhynchines, thus destabilizing the long-favored sub-division of trematosaurids based on their skull shape. We attribute this result to character state conflict and suggest that the traditional classification of trematosaurids may mask more complex evolutionary relationships, as well as possible trophic partitioning, and eco-morphological plasticity.

Variability of isotopic partitioning between sympatric brown trout (Salmo trutta) and European grayling (Thymallus thymallus) in the Loue River (France)

AbstractTrophic partitioning, defining how individuals or populations differ in their resource use, is expected to promote coexistence of sympatric species by reducing resource overlap. We used stable isotope measurements (δ13C and δ15N) to address niche characteristics (δ13C and δ15N ranges, isotope convex hull and standard ellipse areas, mean nearest neighbour distances and trophic positions) and trophic partitioning of sympatric brown trout (Salmo trutta,n = 110) and European grayling (Thymallus thymallus,n = 63) in two sampling locations of a French river. Aquatic resources predominantly fuelled both species, yet both terrestrial resources (TER) and trophic positions (TP) were higher for trout (~36 ± 13% TER, 3.6 ± 0.7 TP) than grayling (~26 ± 9% TER, 2.7 ± 0.6 TP) supporting difference in their trophic niches. Isotope analyses showed that trout had a larger isotope niche than grayling suggesting more opportunistic trophic behaviour. Their isotopic overlapping was higher at the upstream site (isotopic nestedness = 0.8 ± 0.1) than that at the downstream site (isotopic nestedness = 0.4 ± 0.2). Euclidian distances of stable isotopes and TP for the two species increased with salmonid size, while aquatic resource use decreased with salmonid size. These results demonstrate an increase in isotopic niche partitioning and change in trophic attributes with ontogeny. Our study showed that despite relying on similar resources, these two sympatric salmonids exhibited clear trophic differences that were amplified with ontogeny. The consideration of fish ontogenetic dietary shift would hence be a determinant driver of the trophic niche partitioning for these sympatric salmonids.

Nitrogen isotope composition of amino acids reveals trophic partitioning in two sympatric amphipods.

According to ecological theory, two species cannot occupy the same niche. Using nitrogen isotope analyses (δ15N) of amino acids, we tested the extent to which two sympatric deposit‐feeding amphipods, Monoporeia affinis and Pontoporeia femorata, partition their trophic resources. We found that trophic position (TP) and resynthesis index (∑V; a proxy for degradation status of ingested material prior to assimilation by the consumer) differ between species. The surface‐feeding M. affinis had higher TP and intermediate ∑V, both pointing to a large contribution of metazoans in its diet. P. femorata, which feeds in the subsurface layers, had lower TP and a bimodal distribution of the ∑V values, supporting previous experimental evidence of a larger feeding niche. We also evaluated whether TP and ∑V values have consequences for amphipod fecundity and embryo viability and found that embryo viability in M. affinis was negatively linked to TP. Our results indicate that the amino acid‐δ15N data paired with information about reproductive status are useful for detecting differences in the trophic ecology of sympatric amphipods.

Pycnodont fishes (Actinopterygii, Pycnodontiformes) from the Upper Cretaceous (lower Turonian) Akrabou Formation of Asfla, Morocco

The Upper Cretaceous (upper Cenomanian–middle Turonian) Akrabou Formation of Asfla, southeast Morocco is renowned for exceptionally preserved, often three-dimensional bony and cartilaginous fish fossils. Teleosts, rare holosteans and chondrichthyans are well known from the so-called ‘Goulmima ichthyological assemblage’, however pycnodonts (Actinopterygii, Pycnodontiformes) have received scant attention and remain undescribed until now. Five nominal species are recognised in the assemblage, including two new forms: Neomesturus asflaensis gen. et sp. nov. and Paranursallia cavini sp. nov. The Italian genus Polazzodus is reported in Morocco for the first time. Specimen taphonomy is examined in the context of substrate consistency and oxygenation of an outer shelf carbonate platform setting. Diversity and ecological disparity of the Goulmima assemblage is revised in regard to trophic partitioning with durophagy seemingly more diverse than previously recognised. Comparisons with other pycnodont-bearing horizons of similar age demonstrate strong faunal affinities between the Asfla pycnodonts and those in the western Tethys and South Atlantic.