Combination Of Stable Isotopes Research Articles

Chemometric Discrimination of the Geographical Origin of Rheum tanguticum by Stable Isotope Analysis

Rheum tanguticum is one of the primary rhubarb species used for food and medicinal purposes, and it has recently been gaining more attention and recognition. This research represents the first attempt to use stable isotopes and elemental analysis via IRMS to identify the geographical origin of Rheum tanguticum. A grand total of 190 rhubarb samples were gathered from 38 locations spread throughout the provinces of Gansu, Sichuan, and Qinghai in China. The carbon content showed a decreasing trend in the order of Qinghai, followed by Sichuan, and then Gansu. Nitrogen content was notably higher, with Qinghai and Sichuan displaying similar levels, while Gansu had the lowest nitrogen levels. Significant differences were noted in the δ13C (−28.9 to −26.5‰), δ15N (2.6 to 5.6‰), δ2H (−120.0 to −89.3‰), and δ18O (16.0‰ to 18.8‰) isotopes among the various rhubarb cultivation areas. A significant negative correlation was found between %C and both longitude and humidity. Additionally, δ13C and δ15N isotopes were negatively correlated with longitude, and δ15N showed a negative correlation with humidity as well. δ2H and δ18O isotopes exhibited a strong positive correlation with latitude, while significant negative correlations were observed between δ2H and δ18O isotopes and temperature, precipitation, and humidity. The LDA, PLS-DA, and k-NN models all exhibited strong classification performance in both the training and validation sets, achieving accuracy rates between 82.1% and 91.7%. The combination of stable isotopes, elemental analysis, and chemometrics provides a reliable and efficient discriminant model for accurately determining the geographical origin of R. tanguticum in different regions. In the future, the approach will aid in identifying the geographical origin and efficacy of rhubarb in other studies.

Prey contribution to the diet of pink cusk-eel Genypterus blacodes (Forster, 1801) revealed by stomach content and stable isotopic analyses in the southwestern Atlantic

This paper studied the diet of the pink cusk-eel Genypterus blacodes, using a combination of stable isotope (δ13C and δ15N) and stomach content analyses, from specimens captured during eight scientific trawl surveys carried out from 37°S to 53.3°S, and from 65 to 390 m depth. A total of 1615 specimens were analyzed, from which 795 (49.22 %) that ranged from 15 to 114 cm in total length (TL), contained prey. The pink cusk-eel fed mainly on fish and crustaceans. Among fishes, the most important were the notothenioid Patagonotothen ramsayi and the Argentine hake Merluccius hubbsi. The most important crustaceans consumed were the lobster krill Munida gregaria, isopods (Cirolana spp., Serolidae), stomatopods (Pterygosquilla armata) and gammarid amphipods. Ontogenetic diet shifts were detected with the TL, with an increase consumption of fish and a decrease consumption of crustaceans. Moreover, there were changes in the diet associated with depth and region. The isotopic structure of the food chain showed the classic enrichment with trophic level increase. While the stomach contents analysis in a subregion indicated that crustaceans were the predominant prey, followed by cephalopods and fish, Bayesian mixing models showed differential assimilation to pink cusk-eel muscle, with fish as the main assimilated prey and a relatively minimal inputs of crustaceans and cephalopods. Clear distinctions between the pelagic and benthic baselines were detected, with pink cusk-eel participating in both benthic and pelagic pathways. The pink cusk-eel occupied the role of top predator in the Southwestern Atlantic ecosystem (trophic level ∼4) and the δ15N did not exhibit changes with respect to an analyzed specimen of the year 1962.

Origin traceability of bottled mineral water imported into China using chemical and stable isotope fingerprints

A comprehensive study of 96 bottled mineral water (BMW) samples consisting of 21 of the most popular origins and brands sourced from China (n = 38), France (n = 20), Italy (n = 10), New Zealand (n = 17) and Fiji (n = 12) has been undertaken. The δ18O and δ13C of dissolved inorganic carbon (DIC), δ18O and δ2H of water, mineral elements (Li, Na, Mg, K, Ca, Sr) and ions (Cl−, SO42−, F−, CO32−, HCO3−) were investigated and used for origin traceability. The origin of BMW was confirmed by applying Fisher discriminant analysis (Fisher - DA) and artificial neural network (ANN) models to these variables. δ18ODIC, δ13CDIC, δ18O, δ2H values of BMW showed significant deviations with origin. Mineral elements and anions varied widely due to different regional geology and hydrology characteristics. A discriminant model based on Fisher-DA showed that the identification accuracy of mineral water from different origins was in the range of 81 % to 100 %, whereas the discriminant accuracy was 100 % for the training samples and 96.0 % for the testing samples calculated by ANN. HCO3−, NO3−, δ2H, δ18O and F− were the most important variables that characterized BMWs from different origins. Using a combination of stable isotopes and different water chemical components, BMWs from China can be accurately distinguished from other origins using multivariate statistical models.

Combination of Stable Isotopes and Fatty Acid Composition for Geographical Origin Discrimination of One Argan Oil Vintage.

Quality control and traceability of Argan oil requires precise chemical characterization considering different provenances. The fatty acid profile is an essential parameter that certifies the quality and purity of Argan oil. In addition, stable isotopes were recently shown to be accurate as an indicator for geographical origin. In this study, fatty acid composition by gas chromatography (GC) and stable isotope ratio by isotope ratio mass spectrometry (IRMS) were investigated for classifying Argan oil according to its geographical origin. Forty-one Argan oil samples, belonging to six geographical origins of Moroccan natural Argan population (Safi, Essaouira, Agadir Ida Outanane, Taroudant, Tiznit and Sidi Ifni) were collected and extracted under the same conditions. The results show that the isotope δ13C, palmitic acid (C16:0), linoleic acid (C18:2) and unsaturated fatty acids (UFA) were strongly influenced by ecological parameters. Linear discriminant analysis (LDA) was performed to discriminate the six studied provenances. Discriminant models predicted the origin of Argan oil with 92.70% success. Samples from Safi, Essaouira and Agadir Ida Outanane presented the highest classification rate (100%). In contrast, the lowest rate was reported for samples from Tiznit (85.70%). The findings obtained for fatty acids and isotope combination might be considered as an accurate tool for determining the geographical origins of Argan oil. Moreover, they can potentially be used as specific markers for oils labeled with Protected Geographical Indication (PGI).

Analysis and evaluation of the renewability of the deep groundwater in the Huaihe River Basin, China

Groundwater is the major source for resident drinking, industrial development, and agricultural irrigation in the Huai River Basin (HRB). With the development of industry and agriculture, exploitation of the deep groundwater increases dramatically in the HRB in recent years. Therefore, analysis and evaluation the renewability of the deep groundwater in the HRB is critical. In our study, a total of 390 groundwater samples were collected along four profiles in 35 cities and counties within the HRB to obtain their hydrochemical characteristics and isotopic data. Based on the isotopic data of these samples, three deep groundwater subsystems: the Shaying River System, the Guohe River System, and the Ancient Yellow River System were identified. The further comparison indicates that the deep and shallow groundwater systems of Guohe River System and Shaying River System have good differentiation. While, the connection of deep and shallow aquifer of Ancient Yellow River System is strong. According to the calculation results based on the combination of stable isotopes and water chemistry, the renewable ability of deep groundwater of Ancient Yellow River, Shaying river, and Guo river are 36%, 22%, and 12%, respectively, which implies faster renewal rate and greater exploitation potential.

Stable isotopes and epibiont communities reveal foraging habitats of nesting loggerhead turtles in the South West Indian Ocean

Loggerhead sea turtles (Caretta caretta) occupy an array of marine habitats throughout their lives and understanding how this threatened species utilizes these habitats can help guide conservation efforts. This study used a combination of isotopic analysis (δ13C; δ15N) of turtle epidermis and epibiotic community composition to examine habitat-use patterns of nesting loggerheads from the South West Indian Ocean and related these to turtle body condition. First, we identified two foraging groups using relative changes in the turtle’s epidermis δ13C isotope values (of 170 individuals). Second, we show that epibiont communities (of 80 turtles) differed significantly between the two foraging groups, with oceanic/pelagic and neritic/benthic species occurring in higher abundances on turtles with depleted and enriched δ13C values, respectively. The complementary evidence from isotope and epibiont data thus indicates that nesting loggerheads of this population exhibit a bimodal foraging strategy. The relatively high variability in δ13C and δ15N values of the turtles’ tissue showed that they have a broad isotopic niche. While isotopic niches overlapped among turtles with different body conditions, very healthy individuals had a significantly narrower isotopic niche width than those in poorer condition. This suggests that turtles in very good condition are food specialists, and individuals with suboptimal body conditions utilise a wider range of food items and are more generalist foragers. These results show the value of using a combination of stable isotopes and epibiont communities as cost-effective tools that can be applied effectively to derive information on habitat-use patterns of migratory species.

Where Does the Chilean Aconcagua River Come from? Use of Natural Tracers for Water Genesis Characterization in Glacial and Periglacial Environments

The Aconcagua river basin (Chile, 32 °S) has suffered the effects of the megadrought over the last decade. The severe snowfall deficiency drastically modified the water supply to the catchment headwaters. Despite the recognized snowmelt contribution to the basin, an unknown streamflow buffering effect is produced by glacial, periglacial and groundwater inputs, especially in dry periods. Hence, each type of water source was characterized and quantified for each season, through the combination of stable isotope and ionic analyses as natural water tracers. The δ18O and electric conductivity were identified as the key parameters for the differentiation of each water source. The use of these parameters in the stable isotope mixing “simmr” model revealed that snowmelt input accounted 52% in spring and only 22–36% during the rest of the year in the headwaters. While glacial supply contributed up to 34%, both groundwater and periglacial exhibited a remarkable contribution around 20% with some seasonal variations. Downstream, glacial contribution averaged 15–20%, groundwater seasonally increased up to 46%, and periglacial input was surprisingly high (i.e., 14–21%). The different water sources contribution quantification over time for the Aconcagua River reported in this work provides key information for water security in this territory.

Trophic Niche and Diversity of a Pelagic Squid (Dosidicus gigas): A Comparative Study Using Stable Isotope, Fatty Acid, and Feeding Apparatuses Morphology

Commercially important pelagic squid such as jumbo squid Dosidicus gigas play a key role in energy and nutrient transfer in marine ecosystem. Geographic variations in the foraging strategy of D. gigas can provide valuable information on cephalopod trophic diversification and adaption to natural and anthropogenic impacts. Here, we used a novel combination of stable isotope (SI) and fatty acid (FA) analyses of muscle tissues and morphometric measurements of feeding apparatuses to evaluate spatial patterns of habitat and resource use of D. gigas collected from three main fishing grounds in the tropical and southern temperate Pacific Ocean. Results showed that the δ13C and δ15N values were different among geographic stocks within D. gigas, possibly because of site-specific dietary sources and isotopic baseline values. Spatial variabilities in FA profiles/biomarkers, combined with SI results, suggests two foraging patterns: utilization of resources mainly from oceanic food webs or from both neritic and oceanic food webs. This behavior likely promotes the site-specific trophic niche width, increases adaptation to inhabiting oceanographic conditions, and could be driven by differences in feeding apparatuses morphology, body size, and trophic position. These results emphasize the dietary flexibility of D. gigas and their important ecological roles in ecosystems as cross-biome trophic linkages. Trophic diversification of pelagic squid like D. gigas may have important implications for their population dynamics, ecological associations, and subsequent management.

Basal resource quality and energy sources in three habitats of a lowland river ecosystem

AbstractUnderstanding energy flow through ecosystems and among sub‐habitats is critical for understanding patterns of biodiversity and ecosystem function. It can also be of considerable applied interest in situations where managing for connectivity among habitats is important for restoring degraded ecosystems. Here, we describe patterns of basal resource quality and identify primary basal energy sources in three habitats—river channels, anabranches and wetlands—of a lowland river floodplain in the Murray River catchment, Australia during a period of disconnected surface flow. We used a combination of stable isotope and fatty acid analyses to determine which basal resources were assimilated by the backswimmer Anisops thienemanni and the Eastern mosquitofish Gambusia holbrooki and assessed food quality across the three habitats. Seston was a primary basal resource for both animals in all three habitats, but was of higher quality within floodplain habitats than in the river channel. Although floodplain seston contained higher concentrations of essential fatty acids, fatty acid profiles of animals from different habitats remained similar. Our research suggests that inundation of floodplains and subsequent reconnection to the river could be valuable to afford riverine animals the opportunity to access high quality resources, but highlights a need to quantitatively assess the transfer of essential fatty acids between trophic levels to determine how much riverine animals are in fact limited by poorer quality food resources. We demonstrate the importance of estimating the quality of organic matter fluxes into food webs, and the potential role of targeted environmental flows to re‐establish high quality energy pathways in riverine ecosystems.

Combination of stable isotopes and multi-elements analysis with chemometric for determining the geographical origins of Rhizoma Coptidis

Rhizoma Coptidis is a valuable medicine food homology plant, whose geographic origin is a topic of interest to both consumers and producers since the geographic origin determines its prices and efficacy. A novel method for discriminating the geographic origins of Rhizoma Coptidis was established based on stable isotopes and multi-elements analysis combined with chemometric. Then, 4 light stable isotope ratios and 32 inorganic elements of 103 samples from six regions were determined. The results showed that the isotopes ratios and multi-elements contents were significantly different among Rhizoma Coptidis from six regions. Al, Sn, Mg, δ15N and δ13C (VIP > 1.5) were considered as the most powerful differentiation markers for discriminating the geographical origins. In addition, by linear discriminant analysis (LDA) and orthogonal partial least squares discriminant analysis (OPLS-DA), all samples were successfully classified with 100% accuracy. Based on the built predictive model, the origin of unknown samples were successfully predicted with 100% accuracy. The parameters of the models R2X, R2Y and Q2 were 0.999, 0.900 and 0.854, respectively. Therefore, the stable isotopes and multi-elements analysis combined with chemometric tools can be successfully used to discriminate the geographic origins of Rhizoma Coptidis.

Nitrogen uptake regime regulated by ice melting during austral summer in the Prydz Bay, Antarctica

Using a combination of stable isotope (15N) and radionuclide (226Ra) analyses, we examine possible controls on the interactions between melting ice and the uptake of nitrogen in the Prydz Bay during the 2006 austral summer. We find that specific rates of uptake for nitrate and ammonium correlate positively to their concentrations, thus suggesting a substrate effect. In the study area, we observe that regions along open, oceanic water have high f-ratios (nitrate uptake/nitrate+ammonium uptake), while areas near the Amery Ice Shelf have significantly low f-ratios. Further analysis reveals a negative correlation between the f-ratio and the melt water fraction, thus implying that the melting of ice plays an essential role in regulating pelagic N dynamics in the Southern Ocean (SO). Stratification, produced by melting ice, should profoundly affect the efficiency of the SO’s biological pump and consequently affect the concentration of CO2 in the atmosphere. Results presented in this study add information to an already significant base of understanding of the controls on pelagic C and N dynamics in the SO. This provides unique insights for either interpreting past changes in geologic records or for predicting future climate change trends.

Oribatid mites reveal that competition for resources and trophic structure combine to regulate the assembly of diverse soil animal communities.

The role of niche partitioning in structuring species‐rich soil animal communities has been debated for decades and generated the “enigma of soil animal diversity.” More recently, resource‐based niche partitioning has been hypothesized to play a very limited role in the assembly of soil animal communities. To test this hypothesis, we applied a novel combination of stable isotopes and null models of species co‐occurrence to quantify the extent of resource niche partitioning on a diverse oribatid mite community sampled from mature oak woodland.We asked whether species aggregate or segregate spatially and how these patterns correlated with the abundance of estimated trophic guilds. We also estimated the effects of environmental variables on community structure.All measured environmental variables accounted for 12% of variance in community structure, including 8% of pure spatial structure unrelated to measured environmental factors and 2% of pure environmental variance unrelated to spatial variation. Co‐occurrence analysis revealed 10 pairs of species that aggregated and six pairs of species that were spatially segregated. Values of δ15N indicated that five out of the 10 pairs of aggregated species occupied the same trophic guild, while values of δ13C indicated that species in these five pairs consumed resources of different quality, supporting a significant role of resource‐based niche partitioning. Also, one of the five pairs of segregated species occupied the same trophic guild but had overlapping δ13C values suggesting that these species do not co‐occur locally and thus minimize competition for shared resources.Partitioning of resources plays an underestimated role in soil microarthropod communities and different local communities consisted of the same trophic guilds with species identity changing from place to place. The sum of resource partitioning, multi‐trophic interactions, and microscale environmental variability in the environment is a viable solution to the enigma of soil animal diversity.

Trophic Ecology of Sheepshead and Stone Crabs at Oil and Gas Platforms in the Northern Gulf of Mexico's Hypoxic Zone

AbstractOil and gas platforms (platforms) may provide important habitat for reef‐associated organisms in the Gulf of Mexico's hypoxic zone. While summer hypoxia typically affects the bottom 3.0 m of the water column, platforms span from the bottom to above the surface and provide hard substrate in oxygenated waters overlaying hypoxia. However, little is known about the effects of hypoxia on organisms living at these platforms. We compared diets of Sheepshead Archosargus probatocephalus and Gulf stone crabs Menippe adina during early and late summer at platforms with mild (shoal platforms) and intense hypoxia (seaward platforms) using a combination of stable isotopes (δ13C and δ15N) and gut contents analyses. We hypothesized that diets at seaward platforms would shift from bottom to platform‐dwelling prey during late summer when hypoxia had fully developed and decimated benthic communities, but no such effect was found. Barnacles (Balanidae) were the most common prey found in Sheepshead guts for all samples collected (64.1% of gut contents). Sheepshead gut contents showed high predation of mantis shrimp (Squillidae; 35.2% of gut contents) soon after the formation of hypoxia at seaward platforms, likely reflecting Sheepshead exploiting benthic prey that were vulnerable because of hypoxia. These findings indicate that hypoxia affected the behavior of mantis shrimp in a way that altered their availability for Sheepshead associated with platforms. Comparisons of Sheepshead and stone crab isotope values (δ13C and δ15N) to those of their potential prey and basal sources suggested a high dependence on barnacles (proxy for water column particulate organic matter) and filamentous algae throughout the summer. However, comparisons of isotope values in early and late summer indicated no apparent effect of hypoxia. High contributions of barnacles to Sheepshead diet showed that platform‐dwelling prey were an important resource for Sheepshead.

Structural and functional similarity of epibenthic communities on standing and reefed platforms in the northwestern Gulf of Mexico

Fossil fuel extraction in the Gulf of Mexico currently involves the use of approximately 2000 active oil and gas production platforms. These artificial structures provide a number of ecological functions including habitat provision for epibenthic invertebrates and production of food and refuge for a variety of fish species. To mitigate the loss of habitat when active platforms are decommissioned, Rigs-to-Reefs programs maintain existing communities by removing the upper 26 m of platform structure and converting upper and lower portions into artificial reefs. We examined the epibenthic communities of two standing platforms at 5 m and 30 m depths and three reefed platforms at 30 m depths. A combination of stable isotope and community analysis was used to assess the structure and food web functioning of epibenthic communities among these site-types. Reefed platforms (30 m) supported communities with similar food web structure as 5 m and 30 m standing platform communities. However, community composition in standing platform and reefed platform sites at 30 m differed from those of standing platform sites at 5 m depths. Results indicate that, although loss of shallow water habitat associated with platform reefing may diminish some aspects of biodiversity, reefed platforms support similar fundamental ecological functions as standing platforms in the Gulf of Mexico. Thus, the current reefing practice of removal of the upper 26 m of the structure does not substantially influence the functionality of these systems, and the retained structure maintains beneficial habitat for epibenthic communities.

Breastfeeding and weaning in ancient populations: Challenges and future directions

Breastfeeding and weaning in ancient populations: Challenges and future directions

Dietary and seasonal variability in trophic relations at the base of the North Sea pelagic food web revealed by stable isotope and fatty acid analysis

A two-dimensional biomarker approach including fatty acids and stable isotopes of seston and copepods was applied to examine how the variability at the base of the food web affects trophic interactions between primary producers and copepod consumers over a sampling period of two years. We investigated how the composition of the seston affected feeding behaviour by analysing the fatty acid and stable isotope signals of the copepods Calanus helgolandicus, Acartia spp., Centropages spp. and Temora longicornis at Helgoland Roads, North Sea. Our results indicate that the relative contributions of autotrophic and heterotrophic fractions in the seston determined the stable isotope signal of the seston and hence the δ15N of copepods. Our findings show that the combination of stable isotope and fatty acid analyses provides an ideal tool to address the complexity of trophic relations in planktonic food-webs and to define relative trophic position and feeding preferences of e.g. copepods. Defining accurate baselines from bulk seston samples containing a mixture of auto- and heterotroph protist communities still remains a challenge when defining lower food-web dynamics in natural plankton communities.

Asymmetric assimilation of an anthropogenic resource subsidy in a freshwater food web

Anthropogenic subsidies occur readily, especially with growing human development neighboring natural systems. Determining how these subsidies permeate into native food webs is important, but currently not well understood. Here, we used a combination of stable isotopes and fatty acids as bio-tracers to explore the pathway(s) of assimilation of an anthropogenic resource (aquaculture feed) provided by freshwater cage aquaculture. Our results point to an asymmetric assimilation of aquaculture feed by native organisms into and through the food web. Specifically, two pelagic fish species (an intermediate consumer and a top predator) show elevated trophic positions (based on δ15N signatures driven by aquaculture feed) and higher proportions of essential fatty acids (18:2n-6 and 18:3n-3) in waters surrounding the aquaculture facility compared to control sites lacking aquaculture cages, suggesting feed consumption. Fish that appeared to assimilate feed also had higher n-3 long chain poly unsaturated fatty acids (LC PUFA) proportions, indicating a possible role of the feed subsidy for fish health. Alternatively, there was no evidence of feed assimilation through the littoral energy channel. Our findings provide new insight into an emerging research area that asks how anthropogenic resource subsidies affect species health and properties of food webs. Since many habitats experience both natural and anthropogenic subsidy inputs, the multiple tracer approach employed here shows promise for studying how subsidies may affect species health and behavior, as well as food web structure and ultimately stability.

Shallow ponds are biogeochemically distinct habitats in salt marsh ecosystems

AbstractRunaway expansion of shallow ponds can catalyze the conversion of vegetated marshes into open water environments. Predicting how this transition affects ecosystem functioning is difficult because little is known about pond biogeochemistry. We characterized sediment organic matter sources and transformations in three ponds with different plant communities, over alternating periods of tidal isolation and flushing, during summer and fall, using a combination of stable isotopes, lipid biomarkers, and benthic fluxes. Sediment respiration rates (1.66 ± 0.09 mmol C m−2 d−1 to 28.53 ± 7.76 mmol C m−2 d−1) were comparable to shallow estuaries and driven by sulfate reduction. Rates varied across ponds, reflecting differences in summertime Ruppia maritima and macroalgae abundances, but were similar between seasons. Interactions between aboveground plant and sediment bacterial communities translated into distinct biogeochemical processes across the three ponds. Tidal isolation and summer weather intensified plant and bacterial community effects on pond carbon dynamics, resulting in algal biomass and lipid δ13C values that were 3–12‰ enriched, compared to nearby habitats. Surface sediment organic matter mainly derived from pond microalgae and was compositionally distinct from tidal creeks and marshes. Surprisingly, sediment bacteria were not tightly coupled to benthic microalgae but decomposed multiple carbon sources in surface sediments and became increasingly reliant on buried peat at deeper horizons. Pond development over time could largely be explained by sediment respiration and the simultaneous accretion of the surrounding marsh platform. The role of decomposition in pond expansion is consistent with previous assessments based on whole‐pond metabolism rates. Consequently, future pond expansion could alter ecosystem biogeochemistry and reduce carbon storage.

Canopy cover effects on local soil water dynamics in a tropical agroforestry system: Evaporation drives soil water isotopic enrichment

AbstractDespite the widely held assumption that trees negatively affect the local water budget in densely planted tree plantations, we still lack a clear understanding of the underlying processes by which canopy cover influences local soil water dynamics in more open, humid tropical ecosystems. In this study, we propose a new conceptual model that uses a combination of stable isotope and soil moisture measurements throughout the soil profile to assess potential mechanisms by which evaporation (of surface soil water and of canopy‐intercepted rainfall) affects the relationship between surface soil water isotopic enrichment (lc‐excess) and soil water content. Our conceptual model was derived from soil water data collected under deciduous and evergreen plants in a shade grown coffee agroforestry system in Costa Rica. Reduced soil moisture under shade trees during the “drier” season, coinciding when these trees were defoliated, was largely the result of increase soil water evaporation as indicated by the positive relationship between soil water content and lc‐excess of surface soil water. In contrast, the evergreen coffee shrubs had a higher leaf area index during the “drier” season, leading to enhanced rainfall interception and a negative relationship between lc‐excess and soil water content. During the wet season, there was no clear relationship between soil water content and between lc‐excess of surface soil water. Greater surface soil water under coffee during the dry season may, in part, explain greater preferential flow under coffee compared with under trees in conditions of low rainfall intensities. However, with increasing rainfall intensities during the wet season, there was no obvious difference in preferential flow between the two canopy covers. Results from this study indicate that our new conceptual model can be used to help disentangling the relative influence of canopy cover on local soil water isotopic composition and dynamics, yet also stresses the need for additional measurements to better resolve the underlying processes by which canopy structure influences local water dynamics.

Trophic ecology of adult male Odonata. I. Dietary niche metrics by foraging guild, species, body size, and location

1. Information on the dietary niches of adult odonates is sparse, as they are highly mobile and evasive animals, which makes them difficult to observe in their natural habitat. Moreover, there is a lack of knowledge on how varying behavioural traits of odonates relate to phenomena like niche partitioning.2. This study investigated niche partitioning amongst odonate species, foraging guilds and size classes in a riverine system in the Eastern Cape province of South Africa. A combination of stable isotope and fatty acid‐based niches was used to infer odonate feeding.3. Both fatty acid and stable isotope‐based niches showed that there was niche separation amongst odonates that forage in flight (fliers) and those that forage from a perch (perchers), amongst odonates of different size classes (damselflies, medium‐ and large‐sized dragonflies), and amongst species, although varying levels of niche overlap were observed in each case.4. Niche sizes of odonates varied between an upstream and a downstream site. Generally greater niche overlap was recorded at the narrow upstream site (associated with low insect emergence rates) than the wider downstream site (associated with high insect emergence rates), indicating that a greater degree of resource sharing occurred at the upstream site where aquatic food was less abundant.5. The findings of this study suggest that dietary niches of odonates can be influenced by foraging guild, body size, and/or environmental conditions, and additional study in a variety of regions is recommended to determine the greater applicability of these findings.