δ15N Stable Isotope Analysis Research Articles

Assessment of trophic segregation amongst gentoo penguin (Pygoscelis papua) individuals in Antarctica using a non-invasive methodology

Abstract Individual trophic specialization (ITS) refers to the trophic diversification amongst individuals within a population. The gentoo penguin (Pygoscelis papua) is considered a trophic generalist at the population level, but little is known about its individual trophic differentiation. We assessed the degree of ITS at one of its main breeding colonies: Ardley Island, South Shetland Islands. We used skin from 19 dead individuals to determine species and sex by molecular methods and a nail for stable isotope analysis of δ15N and δ13C. Isotopic niche metrics and ITS were estimated for the population and for each sex. We found a moderately high degree of ITS associated with the trophic position of the resources consumed (δ15N) for the population and both sexes, as well as a moderate degree of ITS in the foraging habitat (δ13C) for the population and females. Females showed a higher exclusive niche area, suggesting that they use resources and foraging areas that males do not, probably related to reproductive energy demands. Given the high population density of this species, ITS could function as a mechanism to decrease intraspecific competition. This combination of genetic and isotopic tools allowed us to provide relevant information on the trophic ecology of the gentoo penguin without manipulating animals or using invasive methods.

Niche width and overlap of benthic invertebrates in surf zones increase with distance from the estuarine source of organic matter

Benthic invertebrates in the surf zone of exposed sandy beaches represent important links for energy circulation between benthic and pelagic food webs. This work assesses the trophic ecology of co-occurring epi- and hyper-benthic invertebrates inhabiting the surf zone of sandy beaches located close to an estuarine mouth. It illustrates that different sources of organic matter induce changes in resource utilization. The trophic positions, and the niche width and overlap of species were described using δ13C and δ15N stable isotope analysis. The contribution of different sources to the particulate organic matter was quantified through stable isotopes analysis and fatty acids profiles. Shifts in the trophic niches of dominant species reflected a decrease in the contribution of estuarine carbon to the diets along the coast. This change in contribution of estuarine carbon also influenced trophic niche properties: more diverse resources availability resulted in narrower niches without overlap while less diverse resources resulted in broad isotopic niches and a highest overlap. Results show that spatial variations in the availability of resources can modify carbon pathways and trophic interactions in coastal food webs. Whenever resources are abundant, species display a more specialized diet while food scarcity leads to broader diets, a pattern consistent with the optimal foraging theory. This resource maximization behavior commonly observed in nature is also occurring in surf zone ecosystems.

New insights into the subsistence economy of the Late Bronze Age (1100–400 cal BC) communities in the southeastern Baltic

This paper presents the findings of a research project aimed at reconstructing the subsistence economy of the Late Bronze Age communities in eastern Lithuania. We focused on examining archaeobotanical and zooarchaeological assemblages from three hillforts alongside δ13C and δ15N stable isotope analysis of plant and animal remains. Our results suggest that local populations primarily relied on growing domestic plants and animals for their subsistence. By the Late Bronze Age, they had already adopted a diverse package of cultivated plants, with barley and millet being the main crops. Also, inhabitants relied on pig and goat/sheep as a primary source for their protein intake. Finally, δ13C and δ15N measurements suggest that farmers engaged in intensive agriculture with semi-permanent field systems and moderate application of manure.

Tropical insectivorous birds’ predation patterns that promote forest–farmland trophic connectivity for integrated top–down pest biocontrol

Although conversion of natural forest to agriculture can negatively impact biodiversity in many ways, some affected species may respond by dispersing across the forest–farmland eco-zone, thereby facilitating functional connections through food-web interactions beneficial to crop production and forestry. This study examined patterns of Lepidoptera (butterflies and moths), Hemiptera (bugs), and Coleoptera (beetles) herbivory, and insectivorous bird predation within forest-adjacent farms in western Kenya, and how these processes trophically connect the two ecosystems to promote pest biocontrol. Through δ13C and δ15N stable isotope analyses, proportions of maize, farmland legumes and forest trees in pest diets, and pest-prey in bird’s diets were estimated. Birds’ habitat associations and diet specializations’ influence on pest consumption and basal plant carbon levels in birds’ tissues were determined to evaluate birds’ pest-biocontrol potential. Maize was the mostly consumed plant especially by Lepidoptera, but forest trees were peimarily consumed by Coleoptera and Hemiptera. In turn, Lepidoptera were mainly consumed by forest-associated birds, whereas Hemiptera and Coleoptera were mostly consumed by farmland-associated birds. Thus, birds showed cross-habitat pest consumption tendencies, though diet-specialization was unimportant in predicting those tendencies. Muscicapidae (flycatchers and allies); Hirundinidae (swifts and swallows); Motacillidae (pipits and wagtails); and Ploceidae (weavers) birds showed the highest contributory potential for pest biocontrol of Lepidoptera pests, but Estrildidae (manikins and waxbills), Muscicapidae, and Malaconotidae (boubous and gonoleks) birds showed the best potential against Hemiptera and Coleoptera. Furthermore, more maize basal carbon was assimilated by forest-associated compared to farmland-associated birds, whereas most basal carbon from farmland legumes and forest trees were assimilated by farmland birds, suggesting that unlike pest-prey choice, basal plant carbon pathways to avian insectivorous consumers did not strongly mirror birds’ habitat associations. Lepidoptera and Hemiptera were potentially the most significant interhabitat trophic connector arthropods, and for birds, Muscicapidae, Ploceidae, and Estrildidae. These findings show that such functional connectivity may be enhanced through increasing structural cover elements that promote insectivorous birds’ dispersal between farmland and adjacent forests to boost their pest-regulation ecosystem service contribution. The results serve to inform effective management practices by agronomists, foresters, and land-use planners toward promoting landscape-scale-integrated pest management for sustainable agriculture and biodiversity conservation.

Mesolithic human remains at Cueva de la Cocina: Insights from bioarchaeology and geochemistry

A series of previously unpublished human remains were found at Cueva de la Cocina (Dos Aguas, Valencia, Spain) in excavations from the 1940s and 1970s. Our analyses indicate a minimum of 5 individuals were present in the archaeological deposit, including both adults and children. AMS radiocarbon dating and osteological analysis document ritual defleshing or skinning during the Late Mesolithic, while δ13C and δ15N stable isotope analysis and comparisons to contemporary Mesolithic human remains from the region suggest that these individuals were part of a broader subsistence and cultural network of Holocene hunter-gatherers. Ancient DNA data indicate these late Mesolithic individuals were descendants of a major spread of a new population after a population turnover at the end of the Late Glacial. This research highlights the importance of long-term curation of archaeological finds and revisiting legacy collections.

Diet and Trophic Structure of the Fish Community in a Small Sub-Tropical Lake in Central Mexico

Analyses of trophic structure and feeding habits of the fish community can provide information on the complex biotic and abiotic interactions in lake ecosystems. Based on stomach content and δ13C and δ15N stable isotope analyses, we conducted a comprehensive study of the diet of the fish community and its trophic structure in subtropical Lake Zacapu in central Mexico. Overall, there was good agreement between the results based on the diet and the isotope analysis. Fish diets consisted mainly of aquatic macroinvertebrates, which were abundant in the lake. Most species were secondary consumers and trophic generalists across the four sites and two seasons. The food web structure did not differ significantly between the sites or seasons. Our results suggest a low trophic position of native species having a wide spatial trophic niche and niche width. Trophic diet overlap was greater between native species (especially between species from the same family) than between non-native species. Our study provides new information on the trophic interactions in a subtropical lake, rich in endemic species and an important resource for human communities.

Trophic ecology of crustacean endoparasites Petrarca and Baccalaureus (Ascothoracida, Thecostraca) in scleractinian and zoantharian corals

Coral reefs house a great variety of symbiotic associations, including parasitic ones. One of the crucial issues in host-symbiont interactions is the mode of parasite feeding. Most of the parasitism in scleractinian and zoantharian corals is endosymbiotic (endoparasitic). Their trophic interactions are difficult to identify since they only occur in intact associations. Petrarca and Baccaulareus are endosymbiotic crustaceans. In scleractinian corals, Petrarca forms galls in the coral skeleton. Baccaulareus lives inside zoantharians’ gastric cavities. δ13C and δ15N stable isotope analysis (SIA) of Petrarca and its host (holobiont tissue) Turbinaria revealed similar isotopic signatures of the parasite and host (δ13C, -11.77 to -12.69‰; δ15N, 3.66 to 5.52‰), indicating that Petrarca feeds on its host coral. Petrarca has developed mandibles with a row of sharp and dense teeth to cut coral (holobiont) tissue, while maxillules with compound teeth and massive maxillae are involved in further chewing the food. SIA of Baccaulaureus and its host (holobiont) Palythoa revealed that the parasite and its host differ by >12‰ in δ13C, indicating that Baccalaureus does not feed on its host. The analyzed specimens of Baccalaureus revealed 2 groups with different δ15N values; these specimens may obtain food from different trophic levels. The mouth parts of Baccalaureus have reduced mandibles and maxillules with weak armament. Baccalaureus seems to be an opportunist feeder that steals food directly from the host gastric cavity, resulting in significant variations in δ13C and δ15N values.

Simulation of Smoldering Combustion of Organic Horizons at Pine and Spruce Boreal Forests with Lab-Heating Experiments

Wildfire is a threat for many boreal ecosystems and induces deep modifications in organic horizons. In this paper, we have considered fire-induced changes to the organic horizon properties. The effect of fire was studied by using a forest litter burning experiment. Sample heating was performed in the lab at fixed temperatures (200, 300 and 500 °C), on a set of O horizons developed under pine (Flavocetraria-Pinetum association) and spruce (Piceetum hylocomium splendens association) forest litters. Litters were analyzed in terms of pH, specific electrical conductivity, specific surface area, total carbon (Ctot) and nitrogen (Ntot) content, water-soluble carbon and nitrogen, δ13C and δ15N stable isotope analysis and 13C NMR spectroscopy. The mean pH values increased from ~5 to ~8.2 with an increase in the influence of temperature. The specific electrical conductivity and specific surface area properties increased as well from ~255 to ~432 and from 0.42 to 1.84, respectively. Ctot and Ntot decreased, but at the same time the inorganic carbon content increased. The aromaticity of organic matter after the fire increased. The results of the present study show that organic horizons are changed by wildfire and this discussion made it clear to help with the understanding how fire affects organic matter.

Benthic Invertebrates Abundance and Trophic Links in the Coastal Zone during Cladophora Blooms

The green macroalga Cladophora glomerata, a species typical of brackish water, predominates in most coastal areas of estuarine ecosystems. The present study aimed to determine the current ecological conditions in the Neva estuary (Baltic Sea) when subjected to eutrophication and the summer Cladophora bloom. Macroalgae bloom can result in temporary unfavorable conditions (oxygen depletion and pollution) for invertebrates during macroalgae decomposition, and its contribution to the autochthonous benthic food web remains unclear. We evaluated the Cladophora biomass and the abundance and composition of macro- and meiobenthic invertebrates and traced trophic links in the coastal area of the Neva estuary during the Cladophora bloom. Some species of grazing or omnivorous consumers (nematodes, gastropods, amphipods, insect larvae) reached high abundance in the Cladophora-dominated coastal community. The tracing of food sources in a food chain of the Cladophora-dominated coastal community (macrophytes-grazers-omnivores) were elucidated using dual δ13C and δ15N stable isotope analysis. The results showed that autochthonous organic sources derived from Cladophora at various stages might contribute notably (up to 89%) to the coastal food web, supporting the production of benthic consumers.

An Ecological Profile of Hydropsyche alternans (Trichoptera: Hydropsychidae) in Lake Superior, the Last Stronghold of a Once-Dominant Great Lakes Surf Zone Caddisfly.

Simple SummaryPrior to the invasion and spread of Dreissena mussels in the late 1980s, the nearshore waters of the Laurentian Great Lakes were home to diverse assemblages of native aquatic insects, including the net-spinning caddisfly Hydropsyche alternans, which occurred in rocky surf-exposed habitat throughout the system from Lake Superior downstream to Lake Ontario. These surf zone caddisflies are still abundant in the largely Dreissena-free waters of Lake Superior where the present study was conducted. They have not been reported in the lakes below Lake Superior for decades, and are presumed to have been extirpated from Dreissena-infested habitats. The ecological profile presented here documents the life history of H. alternans in Lake Superior, and reveals details of its feeding biology that shed light on the roles that surf zone net-spinners play in the native nearshore food webs of the Great Lakes. The H. alternans life history in Lake Superior begins in mid-summer shortly after oviposition, which features females swimming to surf-exposed lake bottom substrates. Larval development takes approximately 10 months, but most of it occurs during their first 100 days. Adult emergence is broadly synchronous, with large numbers present from the summer solstice through mid-July. Gut content analyses showed that larvae opportunistically feed on algal, animal, and detrital material of aquatic and terrestrial origin. δ13C and δ15N stable isotope data indicate that they function as omnivores that link coastal, nearshore, and pelagic food webs. These energetic links, and the very existence of surf zone insect assemblages in the Great Lakes, depend on the Dreissena populations in Lake Superior remaining relatively small and isolated.We studied the life history, diet, and trophic ecology of Hydropsyche alternans in four rocky sites located along the south-central coast of Lake Superior. The H. alternans life history and broad trophic niche space were similar to those of its riverine relatives. Quantitative sampling over the course of one ice-free season revealed that most individuals lived univoltine life histories that featured early to mid-summer mating, and oviposition and rapid growth and development through summer into fall. Most individuals overwintered as ultimate or penultimate larval instars. Pupation followed ice-out in the spring. Gut content sampling and δ13C and δ15N stable isotope analyses indicated that the typical larval diet is a mix of benthic, pelagic, and terrestrial food resources, including diatoms, small arthropods, sloughed periphyton, and in one site, fugal hyphae apparently of foredune origin. As a suspension-feeding omnivore that relies on waves and currents to deliver food to its nets, H. alternans larvae form energetic links between coastal, nearshore, and offshore food webs. These connections have been lost throughout the lower Laurentian Great Lakes as a consequence of the invasion and spread of Dreissena mussels.

The integration of millet into the diet of Central Asian populations in the third millennium BC

Stable isotope analyses demonstrate that C4 plants played an important dietary role in Eurasian prehistory. Uncertainty remains, however, about when and how crops were integrated into the diet of Central Asian populations. Here, the authors present δ13C and δ15N stable isotope analysis of human and animal bone collagen from Kyrgyzstan, revealing C4 plant—likely broomcorn millet—consumption in the third millennium BC. Combining this evidence with AMS radiocarbon dating and animal collagen peptide fingerprinting demonstrates that broomcorn millet was consumed by humans and animals during the earliest episodes of the westward spread of this crop plant. The results contribute to debates about the timing and means by which domesticated millets were dispersed across Eurasia.

Eco-engineered mangroves provide complex but functionally divergent niches for estuarine species compared to natural mangroves

There is growing demand for novel coastal protection approaches that also provide co-benefits such as enhanced biodiversity. Rock-fillets, which are used to stabilise eroding banks in estuaries, can be colonised by mangroves, and may provide habitat for estuarine fauna. However, it is unknown whether hybrid mangrove/rock-fillet habitats are functionally equivalent to natural mangroves, for estuarine fauna. To determine whether hybrid mangrove habitats are functionally equivalent to natural mangroves, we used δ13C and δ15N stable isotope analyses to describe the isotopic niche space and overlap of estuarine species in these two habitats across three estuaries in NSW, Australia. Using a Bayesian standard ellipse analysis of isotopic niche area, over half the 12 species observed had larger isotopic niche areas in natural mangroves compared to hybrid habitats, however there were no clear patterns for species between habitats. Natural mangroves and hybrid rock-fillet habitats were isotopically distinct for all species sampled (low proportional overlap, 0–19%) suggesting they are not, at present, wholistically functionally equivalent. Estuarine communities from the two habitat types, however, had similar isotopic niches. Hybrid communities displayed a broader range of δ13C values compared to natural mangroves, suggesting mangrove/rock-fillet habitats have a more diverse range of basal food sources. These findings demonstrate the potential for defence solutions to provide unique co-benefits by supporting food webs, but also that natural habitats provide unique ecosystem services that should be protected and rehabilitated where possible. Future modelling and monitoring of habitat utilisation and species performance could provide further insight into the co-benefits and trade-offs of hybrid habitats.

After the Last Glacial Maximum in the refugium of northern Iberia: Environmental shifts, demographic pressure and changing economic strategies at Las Caldas Cave (Asturias, Spain)

The Late Upper Palaeolithic of Europe, particularly the Last Glacial Maximum (LGM: 26-19 kyr cal BP), was a time of dramatic climatic changes. Fauna, and the humans that preyed on them, were forced to adapt their behaviours in response to climate changes to survive. The Cantabrian Region of northern Spain was continuously inhabited during this period when many other areas of Europe were inhospitable. The site of Las Caldas (Asturias) was repeatedly occupied by hunter-gatherers during the Solutrean (26.1–20.3 kyr cal BP) and Magdalenian (18.5–14.3 kyr cal BP). This paper uses δ13C and δ15N stable isotope analysis of red deer (Cervus elaphus) and Spanish ibex (Capra pyrenaica) remains to reconstruct past environments, ungulate niches and habitats, and to understand how this impacted on their availability as a prey source. Results show that during the Solutrean, cold and potentially wet LGM conditions were experienced and ibex lived in lower altitudes, likely due to reduced vegetation, and even small glaciers on the higher mountain slopes. Improved environmental conditions in the Magdalenian allowed ibex to live in their preferred habitat of higher altitudes. Ameliorated Late Glacial conditions correspond with changing economic hunting strategies at the site. Humans exploited wider ecological zones, over larger distances, which coincides with population growth, and greater connectivity across the Cantabrian region. This research highlights the importance of characterising the complex interactions between humans, animals and environments during the Late Pleistocene and how they responded to rapidly changing environmental conditions.

Trophic ecology of yellowtail rockfish (Sebastes flavidus) during a marine heat wave off central California, USA.

The yellowtail rockfish, Sebastes flavidus, is a widespread and abundant mesopredator in the California Current Large Marine Ecosystem. We utilized stomach content and stable isotope analyses to investigate the trophic ecology of this species at three sites off central California just before (August–October 2013) and during (August and October 2014) a marine heat wave. Sebastes flavidus largely consumed pelagic prey (zooplankton and micronekton). Diets were dominated by tunicates (salps and pyrosomes), pelagic crustaceans (euphausiids, hyperid amphipods, larval decapods), and fishes, with the relative contribution of these prey taxa varying spatially (sample location, longitude, depth) and temporally (year, month), based on complementary multivariate analyses. Prey-specific indices demonstrated that individual S. flavidus diet composition typically was dominated by one of these prey groups, and that prey switching occurred based on the relative availability of prey and their energetic importance. Stable isotope analysis of δ15N indicated that the S. flavidus populations sampled in 2014 had been feeding at an elevated trophic position and more variable prey spectrum relative to 2013, probably as a consequence of greater piscivory and the incorporation of temporal changes in diet composition. Because its opportunistic feeding behavior reflects the dynamism and heterogeneity of the pelagic forage preyscape, S. flavidus may be an important ecosystem indicator species. For example, the novel incorporation of pyrosomes as a large portion of the diet of S. flavidus during 2013–2014 directly related to the massive increase in pyrosome abundance in the California Current during the 2014 marine heat wave.

δ15N-stable isotope analysis of NH x : An overview on analytical measurements, source sampling and its source apportionment.

Agricultural sources and non-agricultural emissions contribute to gaseous ammonia (NH3) that plays a vital role in severe haze formation. Qualitative and quantitative contributions of these sources to ambient PM2.5 (particulate matter with an aerodynamic equivalent diameter below 2.5 µm) concentrations remains uncertain. Stable nitrogen isotopic composition (δ15N) of NH3 and NH4+ (δ15N(NH3) and δ15N(NH4+), respectively) can yield valuable information about its sources and associated processes. This review provides an overview of the recent progress in analytical techniques for δ15N(NH3) and δ15N(NH4+) measurement, sampling of atmospheric NH3 and NH4+ in the ambient air and their sources signature (e.g., agricultural vs. fossil fuel), and isotope-based source apportionment of NH3 in urban atmosphere. This study highlights that collecting sample that are fully representative of emission sources remains a challenge in fingerprinting δ15N(NH3) values of NH3 emission sources. Furthermore, isotopic fractionation during NH3 gas-to-particle conversion under varying ambient field conditions (e.g., relative humidity, particle pH, temperature) remains unclear, which indicates more field and laboratory studies to validate theoretically predicted isotopic fractionation are required. Thus, this study concludes that lack of refined δ15N(NH3) fingerprints and full understanding of isotopic fractionation during aerosol formation in a laboratory and field conditions is a limitation for isotope-based source apportionment of NH3. More experimental work (in chamber studies) and theoretical estimations in combinations of field verification are necessary in characterizing isotopic fractionation under various environmental and atmospheric neutralization conditions, which would help to better interpret isotopic data and our understanding on NHx (NH3 + NH4+) dynamics in the atmosphere.Electronic Supplementary MaterialSupplementary material is available in the online version of this article at 10.1007/s11783-021-1414-6 and is accessible for authorized users. Supplementary material includes supplementary tables on summary of recent isotope-based source apportionment studies on ambient NH3 derived from δ15N(NH3) values (Table A1); and summary of recent isotope-based source apportionment studies on particulate NH4+ derived from δ15N(NH4+) values (Table A2).

Stable Isotopic Dynamics of Juvenile Elasmobranchs in a South Carolina Nursery Area

Stable isotope analysis is an increasingly utilized method for understanding resource usage and partitioning in marine species, including elasmobranch fishes. While the diet of elasmobranchs in Winyah Bay, SC, has been the subject of some preliminary research, diet and trophic relationships in this ecosystem are not yet well understood. This study addresses these knowledge gaps using δ13C and δ15N stable isotope analysis to increase understanding of isotopic niche breadth and overlap among 128 individuals representing 11 sympatric elasmobranch species present in Winyah Bay during the summer months. Overall, our findings support an understanding of Winyah Bay's elasmobranch community as trophically diverse, with some significant isotopic niche overlap among considered species, suggesting the possibility of competition for resources between co-occurring small elasmobranchs. These results suggest elasmobranch predators in the Winyah Bay ecosystem have complex and varied predator–prey relationships.

Novel insights into the diet of southern stingrays and Caribbean whiptail rays

Caribbean whiptail and southern stingrays are large-bodied mesopredators, occupying shallow, nearshore ecosystems of The Bahamas, yet virtually nothing is known of their diet or potential resource competition. We used stomach content analysis via gastric lavage and stable isotope analysis to investigate the diet of 94 Caribbean whiptail rays Styracura schmardae and 112 southern stingrays Hypanus americanus across 3 locations in the central Bahamas. Gastric lavage was used to identify prey consumed and compared to stable isotope analysis of δ15N, δ13C and δ34S of barb, muscle, blood and skin, representing different temporal integration periods. Both species appeared to consume a majority of crustaceans and annelids, although δ13C values suggested that Caribbean whiptail rays have larger isotopic niche space across isotopes sampled (potentially broader diet) than southern stingrays, ranging from 5.82-3.43‰2, and a greater variance in δ13C. This suggests Caribbean whiptail rays potentially feed on prey from either a wider geographic range or from different habitats. Caribbean whiptail and southern stingrays are known to spatio-temporally overlap, and their isotopic niche overlapped by 35.6%. This study represents the first integrated diet estimate for southern stingrays obtained using multiple techniques, and the first ever diet assessment in Caribbean whiptail rays. These data are critical for conservation of coastal ray species and management of coastal and nearshore environments throughout the region.

Tackling the jelly web: Trophic ecology of gelatinous zooplankton in oceanic food webs of the eastern tropical Atlantic assessed by stable isotope analysis

AbstractGelatinous zooplankton can be present in high biomass and taxonomic diversity in planktonic oceanic food webs, yet the trophic structuring and importance of this “jelly web” remain incompletely understood. To address this knowledge gap, we provide a holistic trophic characterization of a jelly web in the eastern tropical Atlantic, based on δ13C and δ15N stable isotope analysis of a unique gelatinous zooplankton sample set. The jelly web covered most of the isotopic niche space of the entire planktonic oceanic food web, spanning > 3 trophic levels, ranging from herbivores (e.g., pyrosomes) to higher predators (e.g., ctenophores), highlighting the diverse functional roles and broad possible food web relevance of gelatinous zooplankton. Among gelatinous zooplankton taxa, comparisons of isotopic niches pointed to the presence of differentiation and resource partitioning, but also highlighted the potential for competition, e.g., between hydromedusae and siphonophores. Significant differences in spatial (seamount vs. open ocean) and depth‐resolved patterns (0–400 m vs. 400–1000 m) pointed to additional complexity, and raise questions about the extent of connectivity between locations and differential patterns in vertical coupling between gelatinous zooplankton groups. Added complexity also resulted from inconsistent patterns in trophic ontogenetic shifts among groups. We conclude that the broad trophic niche covered by the jelly web, patterns in niche differentiation within this web, and substantial complexity at the spatial, depth, and taxon level call for a more careful consideration of gelatinous zooplankton in oceanic food web models. In light of climate change and fishing pressure, the data presented here also provide a valuable baseline against which to measure future trophic observations of gelatinous zooplankton communities in the eastern tropical Atlantic.

Top-down suppression of arthropod herbivory in intercropped maize and organic farms evidenced from δ13C and δ15N stable isotope analyses

Maize is a globally important cereal crop and a staple in sub-Saharan Africa, where it is predominantly grown by small-scale farmers. Its production, however, is undermined by numerous herbivorous arthropods, and agrochemicals used for controlling such pests are increasingly unaffordable. Farmers therefore require cheaper, effective and environmentally sustainable pest management alternatives. This study explored the hypothesis that boosting habitat heterogeneity through organic farming and intercropping enhances arthropod predator-herbivore feeding linkages that naturally suppress herbivory across non-Bt maize fields. To test this, δ13C and δ15N stable isotope analyses were conducted to establish feeding pathways from maize, legume intercrops, and marginal vegetation, through arthropod herbivores and predators across 15 small-scale maize fields in western Kenya. Farming and cropping systems’ roles in trophic linkages were also assessed. Feeding connections and plant food source contributions to arthropod consumer diets were subsequently determined using Bayesian mixing models, and predator relative efficiencies also evaluated. The results showed significantly stronger predator-herbivore trophic linkages within intercropped than monoculture fields, while farming system showed no effect. Herbivores showed stronger connections to crops than to noncrops, suggesting higher vulnerability for crops. For predators, earwigs derived most basal carbon from maize; wasps and predatory beetles, from legumes; ants, from both maize and legumes; and spiders, from both crops and noncrops. Ants and earwigs are important in maize herbivore regulation, particularly for intercropping; wasps and predatory beetles for regulating legume herbivores; and spiders for whole-field herbivore regulation. Most studies have focused on single species at single-trophic levels, but here we demonstrate, for the first time in sub-Saharan Africa, application of stable isotope analyses to characterize multitrophic feeding interactions that indicate effective agronomic practices for fostering top-down arthropod herbivore suppression in non-Bt maize fields. The results are useful in prescribing field practices with low-impact habitat management for sustainable small-scale agriculture rather than pesticide-based arthropod herbivore control.

Intraspecific differences in relative isotopic niche area and overlap of co-occurring sharks

Few studies have assessed whether patterns of resource partitioning among sympatric marine predators vary between different habitats. This type of data is important for understanding food web functioning as well as for supporting an ecosystem-based fisheries management plan. In this study, we used δ13C and δ15N stable isotope analysis to assess the relative isotopic niche area (i.e., which species has the largest and smallest isotopic niche area within a study site) and core isotopic niche overlap between 299 sharks of 11 co-occurring shark species that vary in size, diet and behavior in three coastal study areas in South Florida. Overall, results show that the relative isotopic niche area and patterns of core isotopic niche overlap between some sympatric shark species varied between sites, suggesting plasticity in resource use and competitive interactions between shark species (e.g., 85% of blacktip shark Carcharhinus limbatus standard ellipse area overlapped with the blacknose shark C. acronotus ellipse in Biscayne Bay, but there was no overlap between these species’ ellipses in nearby Florida Bay). Therefore, patterns of resource use and trophic interactions documented among species from one site may not be applicable to a neighboring location. These findings may have implications for food web models that incorporate trophic data from different areas for a species when local data are unavailable.