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Juha Mikola - One of the best experts on this subject based on the ideXlab platform.
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effects of microbivore species composition and basal resource enrichment on Trophic Level biomasses in an experimental microbial based soil food web
Oecologia, 1998Co-Authors: Juha MikolaAbstract:Previous theoretical and empirical evidence suggests that species composition within Trophic Levels may profoundly affect the response of Trophic-Level biomasses to enhanced basal resources. To test whether species composition of microbivorous nematodes has such an effect in microbial-based soil food webs, I created three microcosm food webs, consisting of bacteria, fungi, bacterial-feeding nematodes (Acrobeloides tricornus, Caenorhabditis elegans), fungal-feeding nematodes (Aphelenchus avenae, Aphelenchoides sp.) and a predatory nematode (Prionchulus punctatus). The food webs differed in species composition at the second Trophic Level: food web A included A. tricornus and Aph. avenae, food web B included C. elegans and Aphelenchoides sp., and food web AB included all four species. I increased basal resources by adding glucose to half of the replicates of each food web, and sampled microcosms destructively four times during a 22-week experiment to estimate the biomass of organisms at each Trophic Level. Microbivore species composition significantly affected bacterivore and fungivore biomass but not bacterial, fungal or predator biomass. Greatest bacterivore and fungivore biomass was found in food web A, intermediate biomass in food web AB, and smallest biomass in food web B. Basal resource addition increased the biomass of microbes and microbivores but did not affect predator biomass. Importantly, microbivore species composition did not significantly modify the effect of additional resources on Trophic-Level biomasses. The presence of a competitor reduced the biomass of A. tricornus and Aph. avenae, in that the biomass of these species was less in food web AB than in food web A, whereas the biomass of C. elegans and Aphelenchoides sp. was not affected by their potential competitors. The biomass of Aph. avenae increased with additional resources in the absence of the competitor only, while the biomass of A. tricornus and Aphelenchoides sp. increased also in the presence of their competitors. The results imply that microbivore species composition may determine the second-Level biomass in simple microbe-nematode food webs, but may not significantly affect biomass at other Levels or modify the response of Trophic-Level biomasses to enhanced basal resources. The study also shows that even if the role of predation in a food web is diminished, the positive response of organisms to increased resource availability may still be hindered by competition.
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productivity and Trophic Level biomasses in a microbial based soil food web
Oikos, 1998Co-Authors: Juha Mikola, Heikki SetäläAbstract:Basic Trophic-dynamic models using prey-dependent prey-predator interactions typically predict (1) that the limiting factors, resources and predation, should alternate at adjacent Trophic Levels, and (2) that only biomasses at resource limited Levels should increase when the productivity of a system is increased. However, experimental studies on aquatic systems have shown that biomasses tend to respond to increased productivity at all Trophic Levels. To test the predictions in a terrestrial environment. we performed an experiment with a soil food web. We established three food webs with one, two, or three Trophic Levels in microcosms containing an initially sterilized mixture of leaf litter and raw humus, and increased the productivity with additional glucose in half of the replicates of each food web. The first Trophic Level contained 22 species of bacteria and fungi, the second Level a bacterivorous nematode (Caenorhabditis elegans) and a fungivorous nematode (Aphelenchoides sp.), and the third Level a predatory nematode (Prionchulus punctatus). We sampled the microcosms destructively four times during the 22-week experiment to estimate the Trophic-Level biomasses and soil NH 4 + -N concentration. Evolution of CO 2 was measured to estimate microbial productivity. Microbial productivity was greater and the amount of NH 4 + -N lower in the communities provided with additional energy. The presence of microbivores also resulted in greater microbial productivity than in the pure microbial community. The biomass of microbes and microbivores increased when provided with supplementary energy independently of the number of Trophic Levels in the food web, while the biomass of the predatory nematode did not significantly respond to additional energy. The predatory and the bacterial feeding nematodes limited the biomass of their resources, whereas the fungal biomass was unaffected by the fungivore. The results infer that the biomasses at the first and second Trophic Level were simultaneously limited by resources and predation. which contradicts basic prey-dependent models. Prey refuges provided by soil structure may explain the inability of predators to control their preys as effectively as predicted by these models. Moreover, the results suggest that the nature of Trophic interactions may differ at the bottom and top of soil food webs, and between the fungal and bacterial channels.
Nicholas Polunin - One of the best experts on this subject based on the ideXlab platform.
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Long-term changes in the Trophic Level of western Mediterranean fishery and aquaculture landings
Canadian Journal of Fisheries and Aquatic Sciences, 2003Co-Authors: John K. Pinnegar, Nicholas Polunin, Fabio BadalamentiAbstract:We explored changes in western Mediterranean fishery and aquaculture landings using Trophic Level (TL) estimates derived from nitrogen stable isotope analysis combined with geographically detailed fishery data collated by the General Fisheries Council for the Mediterranean (GFCM). Our analyses confirmed earlier suggestions that there has been a significant decline in the mean Trophic Level of Mediterranean landings (by ~0.15 TL over 26 years). However, this decline is suggested to be almost entirely a result of increased landings of bivalve molluscs from mariculture and not due to changes in landings from capture fisheries. The mean Trophic Level of finfish landings has not changed significantly since 1973, although both fish and total landings have become significantly more diverse. Inspection of small pelagic fish landings revealed a marked decrease in the contribution played by anchovy and replacement of this species by sardine. Since 1981, cage culture of high Trophic Level species such as sea bass (D...
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long term changes in the Trophic Level of the celtic sea fish community and fish market price distribution
Journal of Applied Ecology, 2002Co-Authors: John K. Pinnegar, Carl M Obrien, Simon Jennings, Nicholas PoluninAbstract:Summary 1. The intensive exploitation of fish communities often leads to substantial reductions in the abundance of target species, with ramifications for the structure and stability of the ecosystem as a whole. 2. We explored changes in the mean Trophic Level of the Celtic Sea (ICES divisions VII f‐j) fish community using commercial landings, survey data and estimates of Trophic Level derived from the analysis of nitrogen stable isotopes. 3. Our analyses showed that there has been a significant decline in the mean Trophic Level of survey catches from 1982 to 2000 and a decline in the Trophic Level of landings from 1946 to 1998. 4. The decline in mean Trophic Level through time resulted from a reduction in the abundance of large piscivorous fishes and an increase in smaller pelagic species which feed at a lower Trophic Level. 5. Similar patterns of decline in the Trophic Level of both catches and landings imply that there have been substantial changes in the underlying structure of the Celtic Sea fish community and not simply a change in fishery preferences. 6. We suggest that the reported changes in Trophic structure result from reductions in the spawning stock biomass of traditional target species associated with intensive fishing, together with long-term climate variability. 7. The relative distribution of fish market prices has changed significantly over the past 22 years, with high Trophic Level species experiencing greater price rises than lower Trophic Level species. 8. Although decreased abundance of high Trophic Level species will ultimately have negative economic consequences, the reduction in mean Trophic Level of the fish community as a whole may allow the system to sustain higher fishery yields. 9. Management objectives in this fishery will depend on the relative values that society attaches to economic profit and protein production.
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Long‐term changes in the Trophic Level of the Celtic Sea fish community and fish market price distribution
Journal of Applied Ecology, 2002Co-Authors: John K. Pinnegar, Simon Jennings, Carl M. O'brien, Nicholas PoluninAbstract:Summary 1. The intensive exploitation of fish communities often leads to substantial reductions in the abundance of target species, with ramifications for the structure and stability of the ecosystem as a whole. 2. We explored changes in the mean Trophic Level of the Celtic Sea (ICES divisions VII f‐j) fish community using commercial landings, survey data and estimates of Trophic Level derived from the analysis of nitrogen stable isotopes. 3. Our analyses showed that there has been a significant decline in the mean Trophic Level of survey catches from 1982 to 2000 and a decline in the Trophic Level of landings from 1946 to 1998. 4. The decline in mean Trophic Level through time resulted from a reduction in the abundance of large piscivorous fishes and an increase in smaller pelagic species which feed at a lower Trophic Level. 5. Similar patterns of decline in the Trophic Level of both catches and landings imply that there have been substantial changes in the underlying structure of the Celtic Sea fish community and not simply a change in fishery preferences. 6. We suggest that the reported changes in Trophic structure result from reductions in the spawning stock biomass of traditional target species associated with intensive fishing, together with long-term climate variability. 7. The relative distribution of fish market prices has changed significantly over the past 22 years, with high Trophic Level species experiencing greater price rises than lower Trophic Level species. 8. Although decreased abundance of high Trophic Level species will ultimately have negative economic consequences, the reduction in mean Trophic Level of the fish community as a whole may allow the system to sustain higher fishery yields. 9. Management objectives in this fishery will depend on the relative values that society attaches to economic profit and protein production.
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weak cross species relationships between body size and Trophic Level belie powerful size based Trophic structuring in fish communities
Journal of Animal Ecology, 2001Co-Authors: Simon Jennings, John K. Pinnegar, Nicholas Polunin, Trevor W BoonAbstract:1. Body size determines rates of respiration and production, energy requirements, mortality rates, patterns of predation and vulnerability to mortality. Body size distributions are often used to describe structure and energy flux in communities and ecosystems. 2. If clear relationships can be established between body size and Trophic Level in fishes, they may provide a basis for integrating community and ecosystem analyses based on size spectra, food webs and life histories. 3. We investigated relationships between the body sizes (weight and length) of northeast Atlantic fishes and their Trophic Level. The abundance of 15N, as determined by stable isotope analysis, was used as an index of Trophic Level. 4. Cross-species and comparative analyses demonstrated that body size was unrelated or weakly related to Trophic Level. Thus allometric relationships between body size and Trophic Level could not be used to predict the Trophic structure of fish communities. 5. The results of the cross-species analyses contrasted with patterns in the size and Trophic structure of entire fish communities. When fish communities were divided into size classes, there were strong positive relationships between size class and Trophic Level. The slope suggested a mean predator: prey body mass ratio of 80:1. 6. Our results suggest that body size does not provide a useful surrogate of Trophic Level for individual species, but that body size is an excellent predictor of Trophic Level within the community, providing an empirical basis for integrating community analyses based on models of Trophic structure and body size distributions.
Rona A R Mcgill - One of the best experts on this subject based on the ideXlab platform.
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stable isotopes demonstrate intraspecific variation in habitat use and Trophic Level of non breeding albatrosses
Ibis, 2020Co-Authors: William F Mills, Rona A R Mcgill, Yves Cherel, Stephen C Votier, Richard A PhillipsAbstract:The non‐breeding period is critical for restoration of body condition and self‐maintenance in albatrosses, yet detailed information on diet and distribution during this stage of the annual cycle is lacking for many species. Here, we use stable isotope values of body feathers (δ13C, δ15N) to infer habitat use and Trophic Level of non‐breeding adult Grey‐headed Albatrosses Thalassarche chrysostoma (n = 194) from South Georgia. Specifically, we: (i) investigate intrinsic drivers (sex, age, previous breeding outcome) of variation in habitat use and Trophic Level; (ii) quantify variation among feathers of the same birds; and (iii) examine potential carry‐over effects of habitat use and Trophic Level during the non‐breeding period on subsequent breeding outcome. In agreement with previous tracking studies, δ13C values of individual feathers indicate that non‐breeding Grey‐headed Albatrosses from South Georgia foraged across a range of oceanic habitats, but mostly in subantarctic waters, between the Antarctic Polar Front and Subtropical Front. Sex differences were subtle but statistically significant, and overlap in the core isotopic niche areas was high (62%); however, males exhibited slightly lower δ13C and higher δ15N values than females, indicating that males forage at higher latitudes and at a higher Trophic Level. Neither age nor previous breeding outcome influenced stable isotope values, and we found no evidence of carry‐over effects of non‐breeding habitat use or Trophic Level on subsequent breeding outcome. Repeatability among feathers of the same individual was moderate in δ13C and low in δ15N. This cross‐sectional study demonstrates high variability in the foraging and migration strategies of this albatross population.
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variability of higher Trophic Level stable isotope data in space and time a case study in a marine ecosystem
Rapid Communications in Mass Spectrometry, 2015Co-Authors: Petra Quillfeldt, Rona A R Mcgill, Klemens Ekschmitt, Paul Brickle, Volkmar Wolters, Nina Dehnhard, Juan F MaselloAbstract:RATIONALE: 1In shelf and coastal ecosystems, planktonic and benthic Trophic pathways differ in their carbon stable isotope ratios (δ(13)C values) and nitrogen stable isotope ratios (δ(15)N values) and they increase predictably with Trophic Level. Stable isotope data are therefore used as a tool to study food webs in shelf and coastal ecosystems, and to assess the diets and foraging behaviour of predators. However, spatial differences and temporal changes in prevailing environmental conditions and prey abundance may lead to considerable heterogeneity in stable isotope values measured in focal animal species. METHODS: Here we assess spatial and temporal variability of δ(13)C and δ(15)N values in tissue samples of fish, squid and crustacean species captured over three years during research cruises close to the Falkland Islands, Southwest Atlantic. RESULTS: Both in δ(15)N values and especially in δ(13)C values, intra-species differences were large and often exceeded inter-species differences. Spatial patterns were weak, albeit statistically significant. The distribution of δ(13)C values was related to latitude, while the δ(15)N values varied with longitude. The distance from the coast and depth of catch influenced both δ(13)C and δ(15)N values. However, the importance of temporal variability greatly exceeded that of spatial variability. In addition to a moderate overall seasonal effect, we found that species differed strongly in their specific seasonal changes. CONCLUSIONS: Seasonal differences in the relative position of species or species groups in the C-N isotope space suggest changes in the utilisation of planktonic vs. benthic Trophic pathways, indicating flexible foraging strategies in response to variable environmental conditions. These seasonal differences should be taken into account when analysing higher Trophic Level feeding ecology with stable isotope analysis.
William F Mills - One of the best experts on this subject based on the ideXlab platform.
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stable isotopes demonstrate intraspecific variation in habitat use and Trophic Level of non breeding albatrosses
Ibis, 2020Co-Authors: William F Mills, Rona A R Mcgill, Yves Cherel, Stephen C Votier, Richard A PhillipsAbstract:The non‐breeding period is critical for restoration of body condition and self‐maintenance in albatrosses, yet detailed information on diet and distribution during this stage of the annual cycle is lacking for many species. Here, we use stable isotope values of body feathers (δ13C, δ15N) to infer habitat use and Trophic Level of non‐breeding adult Grey‐headed Albatrosses Thalassarche chrysostoma (n = 194) from South Georgia. Specifically, we: (i) investigate intrinsic drivers (sex, age, previous breeding outcome) of variation in habitat use and Trophic Level; (ii) quantify variation among feathers of the same birds; and (iii) examine potential carry‐over effects of habitat use and Trophic Level during the non‐breeding period on subsequent breeding outcome. In agreement with previous tracking studies, δ13C values of individual feathers indicate that non‐breeding Grey‐headed Albatrosses from South Georgia foraged across a range of oceanic habitats, but mostly in subantarctic waters, between the Antarctic Polar Front and Subtropical Front. Sex differences were subtle but statistically significant, and overlap in the core isotopic niche areas was high (62%); however, males exhibited slightly lower δ13C and higher δ15N values than females, indicating that males forage at higher latitudes and at a higher Trophic Level. Neither age nor previous breeding outcome influenced stable isotope values, and we found no evidence of carry‐over effects of non‐breeding habitat use or Trophic Level on subsequent breeding outcome. Repeatability among feathers of the same individual was moderate in δ13C and low in δ15N. This cross‐sectional study demonstrates high variability in the foraging and migration strategies of this albatross population.
Juan F Masello - One of the best experts on this subject based on the ideXlab platform.
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variability of higher Trophic Level stable isotope data in space and time a case study in a marine ecosystem
Rapid Communications in Mass Spectrometry, 2015Co-Authors: Petra Quillfeldt, Rona A R Mcgill, Klemens Ekschmitt, Paul Brickle, Volkmar Wolters, Nina Dehnhard, Juan F MaselloAbstract:RATIONALE: 1In shelf and coastal ecosystems, planktonic and benthic Trophic pathways differ in their carbon stable isotope ratios (δ(13)C values) and nitrogen stable isotope ratios (δ(15)N values) and they increase predictably with Trophic Level. Stable isotope data are therefore used as a tool to study food webs in shelf and coastal ecosystems, and to assess the diets and foraging behaviour of predators. However, spatial differences and temporal changes in prevailing environmental conditions and prey abundance may lead to considerable heterogeneity in stable isotope values measured in focal animal species. METHODS: Here we assess spatial and temporal variability of δ(13)C and δ(15)N values in tissue samples of fish, squid and crustacean species captured over three years during research cruises close to the Falkland Islands, Southwest Atlantic. RESULTS: Both in δ(15)N values and especially in δ(13)C values, intra-species differences were large and often exceeded inter-species differences. Spatial patterns were weak, albeit statistically significant. The distribution of δ(13)C values was related to latitude, while the δ(15)N values varied with longitude. The distance from the coast and depth of catch influenced both δ(13)C and δ(15)N values. However, the importance of temporal variability greatly exceeded that of spatial variability. In addition to a moderate overall seasonal effect, we found that species differed strongly in their specific seasonal changes. CONCLUSIONS: Seasonal differences in the relative position of species or species groups in the C-N isotope space suggest changes in the utilisation of planktonic vs. benthic Trophic pathways, indicating flexible foraging strategies in response to variable environmental conditions. These seasonal differences should be taken into account when analysing higher Trophic Level feeding ecology with stable isotope analysis.
