1,720,990 research outputs found
Isotopic determination of the trophic ecology of a ubiquitous key species. The crab Liocarcinus depurator (Brachyura: Portunidae)
No full textKnowledge of the trophic ecology of predators is key to understanding how they affect food web structure and ecosystem functioning. The harbour crab Liocarcinus depurator (L.) (Brachyura: Portunidae)
is one of the most abundant decapod species in soft-bottom areas of the Mediterranean Sea and northeast Atlantic Ocean. It is both a common prey and predator of commercial and non-commercial
marine species and its predation pressure appears to have little effect on the subtidal community assemblage. However, there are few studies of its diet and little is known about its role in mediating
energy flows in marine ecosystems. In this study, carbon (d13C) and nitrogen (d15N) stable isotope analysis (SIA) and Bayesian analytical tools were used to characterise the trophic niche of L. depurator and
to quantify the most important prey supporting this species under various environmental conditions. Specimens of L. depurator, their potential prey and basal resources were collected from two different
subtidal areas of the Gulf of Gaeta, one affected by human activities (north side) and the other seasonally influenced by freshwater inputs originating from the River Garigliano (south side). While there were
differences between the two sampling areas in terms of the abundance and d15N and d13C values of the macrobenthic prey community, no differences in the d15N values and trophic position of L. depurator
were observed. Specifically, Bayesian mixing models showed Polychaeta Errantia as the main source of crab diets in both areas. The observed differences in the d13C values and the analysis of trophic pathways also indicate that the terrestrial organic matter originating from the discharge of the River Garigliano was integrated along the food web up to L. depurator. Although this species is usually considered an opportunistic feeder, it appears to be highly selective and its trophic habits did not influence food web topology, which in contrast was found to be strongly influenced by River Garigliano discharge
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
Effect of habitat degradation on competition, carrying capacity, and species assemblage stability
Full text linkIn human-impacted rivers, nutrient pollution
has the potential to disrupt biodiversity organisation
and ecosystem functioning, prompting calls for
effective monitoring and management. Pollutants,
together with natural variations, can modify the
isotopic signature of aquatic organisms. Accordingly,
we explored the potential of isotopic variations as an
indicator of drainage basin influences on river food
webs. We assessed stable N and C isotopes within six
food webs along a river affected by multiple pollution
sources. CORINE land cover maps and Digital
Elevation Models (DEMs) were also applied to
understand the impact on surface waters of anthropogenic
pressures affecting the catchment. N isotopic
signatures of taxa fell in association with ammonium
inputs from agriculture, indicating that nitrogen pollution
was related to synthetic fertilizers. Isotopic
variations were consistent across trophic levels, highlighting
site-specific communities and identifying taxa
exposed to pollutants. This allowed us to locate point
sources of disturbance, suggesting that food web
structure plays a key role in pollutant compartmentalisation
along the river. Thematic maps and DEMs
helped understand how the anthropogenic impact on
river biota is mediated by hydro-geomorphology.
Thus, the integration of site-scale analyses of
stable isotopes and land use represents a promising
research pathway for explorative nutrient pollution
monitoring in human-impacted rivers
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
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
Effects of terrestrial input on macrobenthic food webs of coastal sea are detected by stable isotope analysis in Gaeta Gulf
No full textStable isotope analysis (SIA) of carbon (δ13C) and nitrogen (δ15N) was used to analyse the macrobenthic food web dynamics in the Gulf of Gaeta (Tyrrhenian sea, Central Italy) under the influence of discharge from the river Garigliano. Specimens of macrobenthic invertebrates and organic matter (Phytoplankton, detritus and Sediment Organic Matter, SOM) were sampled in eight subtidal sampling sites in the Gulf and subjected to SIA. Bayesian Stable Isotope Mixing Models were used to quantify the proportional contribution of each basal resource to macrobenthic primary consumer diets. The food web topology of each sampling site was also reconstructed and the key food web metrics (connectance, linkage density, mean chain length) were calculated in order to detect potential effects of the river plume at all trophic levels. The δ13C signatures of basal resources indicated that bulk organic matter in the Gulf has two main inputs: a) autochthonous, derived from marine primary producers (phytopla
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
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
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