1,720,974 research outputs found
From shore to the bottom: detecting anthropogenic nitrogen inputs on Lake Bracciano through δ15N of epilithon and Characeae.
No full textNitrogen inputs represent a notable threat for aquatic ecosystem structure and functioning, promoting
cultural eutrophication and algal blooms. Detecting external N inputs is particularly complicated due to the
combined effects of dilution and assimilation processes. Moreover, in monitoring aimed at managing
eutrophication, it is crucial to determine the sources of pollution. Due to its ability to reflect the ‘organic’ or
‘inorganic’ origin of the inputs, the nitrogen isotopic signature of algal primary producers (δ15N) is currently
recognized as a flexible tool in the environmental monitoring of nitrogen pollution. In this study, we tested
the ability of δ15N signatures of Characeae species to intercept the nitrogen inputs spreading from the
coastline to depth in a lacustrine ecosystem. The results of this study highlighted the usefulness of Characeae
for detecting sources of N inputs. We observed a rapid decrease in the nitrogen isotopic values along the
bathymetry, from 0 to 15 meters depth, in the sampling sites characterized by steep slopes (North and East),
while, in the sampling sites with a steep slope (South and West) we observed a propagation effect form the
shoreline (0 m) to the first 5 meters. Moreover, we found a decrease in Characeae occurrence compared with
previous studies. This reduction is likely related to the effects of the recent drought and water level reductionthat affected the investigated lake
Spatial and temporal diet variability of Adélie (Pygoscelis adeliae) and Emperor (Aptenodytes forsteri) Penguin. A multi tissue stable isotope analysis
Full text linkThe Ross Sea, Antarctica, supports large populations of Emperor Penguin (Aptenodytes forsteri) and Adélie Penguin (Pygoscelis adeliae), two key meso-predators that occupy high trophic levels. Despite these species are largely studied, little is known about their diet outside the breeding period. In the present study, we investigated the intra-annual diet of Adélie and Emperor Penguins belonging to five colonies in the Ross Sea through the stable isotope analysis of different tissues (feathers and shell membranes), synthetized in different seasons, and guano that indicates recent diet. Penguin samples and prey (krill and fish) were collected during the Antarctic spring–summer. δ13C and δ15N of tissues and guano indicate spatio-temporal variation in the penguin diet. The krill consumption by Adélie Penguins was lowest in winter except in the northernmost colony, where it was always very high. It peaked in spring and remained prevalent in summer. The greatest krill contribution to Emperor Penguin’s diet occurred in summer. The relative krill and fish consumption by both species changed in relation to the prey availability, which is influenced by seasonal sea ice dynamics, and according to the penguin life cycle phases. The results highlight a strong trophic plasticity in the Adélie Penguin, whose dietary variability has been already recognized, and in the Emperor Penguin, which had not previously reported. Our findings can help understand how these species might react to resource variation due to climate change or anthropogenic overexploitation. Furthermore, data provides useful basis for future comparisons in the Ross Sea MPA and for planning conservation actions
Trophic attractiveness for soil fauna of residues of Bt and near-isogenic maize. A C and N stable isotope-based study
No full textGenetically modified (GM) crops are considered a good way to reduce insecticide use and the presence of certain agricultural pests, thus improving food and environmental safety. Nevertheless, effects of GM plant residues on the soil food web are still poorly understood. Zea mays L., enriched with a gene from Bacillus thuringiensis Berliner subsp. kurstaki (Bt) as a defence against the maize borer, is widely cultivated. In this study, we explored the in- vertebrate food webs associated with residues of Bt and non-Bt maize, respectively represented by DKC6575, with a Cry1Ab transgene (event MON810), and its near-isogenic Tietar variety, in a five-month field experiment. C and N stable isotopes and Bayesian mixing models were used to assess trophic niche metrics and track nutrient flows from maize residues and weeds occurring in maize crops to invertebrate detritivores and predators. While there were no initial differences in the structural components of maize residues between varieties, after five months of exposure in the field, the lignin content was higher and the organic matter content was lower in non-Bt than in Bt maize. Organic matter depletion over time was associated with a decrease in primary consumer abun- dance and an increase in their trophic niche width in both Bt and non-Bt maize, but it was faster in the former. The abundance of primary consumers and predators was higher in non-Bt than in Bt maize, but the distribution of organisms across trophic levels differed between varieties, with prey availability being lower in non-Bt than in Bt maize. This allowed Bt-associated predators to maintain a diet based primarily on the maize food chain through- out the experimental period. In contrast, non-Bt-associated predators were more dependent on weed-feeding prey by the end of the experiment, increasing the coupling between the maize and weed energy channels in the soil food web. Some taxon-specific effects were evident. Less vagile organisms such as Diptera had a specific diet mostly related to maize regardless of variety and time, while the diets of more vagile organisms like Coleoptera and Opiliones changed the most over time. Overall, our results suggest that the attractiveness of non-Bt maize residues for invertebrate consumers is higher than the Bt variety, although the higher recalcitrant content follow- ing decomposition reduces it over time. The attractiveness also affects the movement of invertebrate predators (potentially including pest control agents) and thus nutrient flows in tri-trophic detritus-based food webs in culti- vated and uncultivated plots
Role of body size and habitat complexity in the diet of the invasive Micropterus salmoides (Lacépède). Optimal foraging theory matters
No full textAlthough biological invasions are becoming more frequent, their underlying ecologi- cal mechanisms often remain unknown. One of the most poorly understood aspects is the relationship between ontogenesis and the trophic role of alien spe- cies in invaded ecosystems. The aim of this study was to investigate the role of littoral habitat complexity in the shift from benthivory to piscivory of Microp‐ terus salmoides, one of the most widely introduced and invasive fish species. Specifically, populations from two habitats differing in terms of aquatic veg- etation cover within the same ecosystem were stud- ied. Specimens of M. salmoides and its potential prey collected in both habitats were analyzed for C and N stable isotopes. The consumption of macroinverte- brates decreased with body size, but in the less com- plex habitat, M. salmoides shifted its diet to piscivory at an earlier stage of its life cycle. In this habitat, the size-based food web appears highly connected, as largemouth bass have diffuse weak interactions with multiple prey species occupying a range of trophic levels. This may lead bass to threaten the native fish not only by competition but also by predation. Large piscivorous individuals preferred conspecific fry as prey, on which they concentrated particularly in the more complex habitats, where diet specialization was marked. Since preying on conspecifics is energetically costly, according to Optimal Foraging Theory it only becomes advantageous when competition for other food items is intense. This evident trophic plasticity may favor the success of bass in invaded ecosystems and should be considered when deciding management policy, which should also include the preservation of habitat complexity
Species richness and vulnerability to disturbance propagation in real food webs
Full text linkA central issue in ecology is understanding how complex and biodiverse food webs persist in the face of disturbance, and which structural properties affect disturbance propagation among species. However, our comprehension of assemblage mechanisms and disturbance propagation in food webs is limited by the multitude of stressors affecting ecosystems, impairing ecosystem management. By analysing directional food web components connecting species along food chains, we show that increasing species richness and constant feeding linkage density promote the establishment of predictable food web structures, in which the proportion of species co-present in one or more food chains is lower than what would be expected by chance. This reduces the intrinsic vulnerability of real food webs to disturbance propagation in comparison to random webs, and suggests that biodiversity conservation efforts should also increase the potential of ecological communities to buffer top-down and bottom-up disturbance in ecosystems. The food web patterns observed here have not been noticed before, and could also be explored in non-natural networks
Intraspecific variation in the functional responses of an invasive tropical freshwater fish under increasing temperature regimes
Full text linkGlobal warming and the introduction of non-native fish represent major threats to freshwater biodiversity worldwide, but their effects have usually been investigated separately. Since most fish are ectotherms, their metabolism and feeding behaviour are highly influenced by temperature. Increasing water temperatures may thus exacerbate the impact of non-native fish, particularly those adapted to warmer conditions, on prey populations. Increasing temperature can also result in divergences between the impacts of females and males, especially in sexually dimorphic species.The globally invasive tropical guppy Poecilia reticulata Peters, a popular aquarium fish also used for control of mosquito-borne diseases and as a model species in ecological and evolutionary studies, exhibits strong sexual dimorphism and larvivory. This laboratory study examined prey consumption and prey size selection by guppies fed with chironomid larvae under varying temperature conditions. The effect of sex, pregnancy and prey body size on the guppy's predatory response was also assessed by comparing Functional Responses.The results highlighted four key points: (1) increased temperature led to increased prey consumption in both females and males by decreasing handling time; (2) prey consumption was disproportionately higher in females than males, regardless of temperature; (3) temperature influenced females' prey size selection; and (4) pregnancy reduced prey handling time among females.These findings show that temperature and intraspecific differences influence the feeding response of invasive fish, and they should both be taken into account when investigating and predicting the ecological impact of invasive species on invaded food webs
Individual diet variability shapes the architecture of Antarctic benthic food webs
Full text linkAntarctic biodiversity is affected by seasonal sea-ice dynamics driving basal resource availability. To (1) determine the role of intraspecific dietary variability in structuring benthic food webs sustaining Antarctic biodiversity, and (2) understand how food webs and the position of topologically central species vary with sea-ice cover, single benthic individuals’ diets were studied by isotopic analysis before sea-ice breakup and afterwards. Isotopic trophospecies (or Isotopic Trophic Units) were investigated and food webs reconstructed using Bayesian Mixing Models. As nodes, these webs used either ITUs regardless of their taxonomic membership (ITU-webs) or ITUs assigned to species (population-webs). Both were compared to taxonomic-webs based on taxa and their mean isotopic values. Higher resource availability after sea-ice breakup led to simpler community structure, with lower connectance and linkage density. Intra-population diet variability and compartmentalisation were crucial in determining community structure, showing population-webs to be more complex, stable and robust to biodiversity loss than taxonomic-webs. The core web, representing the minimal community ‘skeleton’ that expands opportunistically while maintaining web stability with changing resource availability, was also identified. Central nodes included the sea-urchin Sterechinus neumayeri and the bivalve Adamussium colbecki, whose diet is described in unprecedented detail. The core web, compartmentalisation and topologically central nodes represent crucial factors underlying Antarctica’s rich benthic food web persistence
First record of the Asian freshwater fish Pseudorasbora parva (Temminck and Schlegel, 1846) from Lake Bracciano (Central Italy)
Full text linkThe presence of the cyprinid Pseudorasbora parva is here reported for the first time in Lake Bracciano (Central Italy), a dormant volcanic lake not connected to other water bodies. The lake, historically classified as oligo-mesotrophic, has a surface area of 57 km2 and its maximum depth is 165 m. Pseudorasbora parva specimens were first collected during a fish community survey in 2017 and again in 2022. Their total length and body weight ranged from 21 and 81 mm and from 0.25 and 6.43 g, respectively. Since Lake Bracciano is not part of a system of connected water bodies, this record could be evidence of at least a translocation event prior to the first record of 2017, suggesting the need for additional studies and measures to deal with the spread of this invasive species
New epilithic δ15N-based analytical protocol for classifying Nitrogen impact in Lake Bracciano
No full textNitrogen inputs in aquatic ecosystems are increasing and climate change is likely to exacerbate cultural eutrophication. The recovery of aquatic ecosystem functionality requires strenuous efforts and entails considerable costs. Therefore, the development of early warning ecological indicators that can help arrest the phenomenon in its early stages is highly desirable. Stable isotope analysis of Nitrogen in algal primary producers has proved useful in determining the origins of Nitrogen inputs in several marine and freshwater ecosystems. Nitrogen signatures are often assigned to impact or non-impact classes by comparing the Nitrogen signature of samples with the Nitrogen signature ranges of potential sources, which can hinder objective ecological evaluation when sample signatures are close to the upper/lower boundaries of source ranges. To overcome this problem, we obtained the Nitrogen signatures of the epilithic associations collected in the littoral zone of Lake Bracciano (Central Italy), covering a pre-drought (2015–2016) and ongoing drought (2017–2019) period. The Bayesian Gaussian Mixture Model determined four probability distributions, each associated with a Nitrogen impact class, and assigned the observed epilithic signatures to the most appropriate classes. Application of the approach at various spatial and temporal scales allowed us to compare the pre-drought and ongoing drought Nitrogen input dynamics. At each spatial and temporal scale, we observed differences in the input dynamics arising from the side effects of the drought on human activities, which were reflected in changes in the probability of Nitrogen signatures belonging to one or the other impact class. Based on this probability, the proposed analytical protocol provided a useful tool for prioritizing specific management measures in areas affected by specific Nitrogen inputs. Moreover, with a few recalibrations, the model proposed for Lake Bracciano can be extended to other contexts
) in structurally different artificial ponds based on stomach contents and stable isotope analyses
No full textIn order to evaluate the effects of ecological disturbances, such as climate change, human-induced habitat modification, or species introduction, and in order to adopt appropriate management policies for their conservation, knowledge of the trophic ecology of protected or threatened species is crucial. The Italian crested newt, Triturus carnifex (Laurenti, 1768), is listed in annexes II and IV of the European Habitats Directive. For this species, changes in water quality and habitat loss represent major threats, potentially impairing its breeding and feeding activities. Artificial aquatic habitats, such as cattle-drinking pools, represent valuable refuges and suitable breeding sites for T. carnifex. The aim of this study was to determine the food niche of the Italian crested newt in these habitats, evaluating its prey selection strategy in relation to a range of environmental conditions and differing availability of resources. Stomach contents (indicative of short-term diet) and δ13C and δ15N signatures of tails (indicative of medium-term diet) of adult newts from three artificial ponds in central Italy, where traditional silvo-pastoral activities are still important, were determined. Potential prey were also sampled and processed for stable isotope analysis. Triturus carnifex, similar to other newt species, is an opportunistic predator, feeding on a wide variety of prey that includes terrestrial and aquatic macroinvertebrates. In particular, the opportunistic use of temporally available small zooplankton was identified from stomach contents analysis. Conversely, stable isotope analysis highlighted the consumption of larger, soft-bodied prey that the stomach-contents-based approach underestimated. These included terrestrial oligochaetes, which turned out to be the most important and energy-rich food source in the medium term. These results emphasize the usefulness of combined approaches for studying the trophic ecology of salamanders and also highlight the importance of the integrated management of aquatic breeding habitats and neighbouring terrestrial habitats, as sources of food, for newt conservation
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