Most stoichiometric models do not consider the importance of ontogenetic changes in body nutrient... more Most stoichiometric models do not consider the importance of ontogenetic changes in body nutrient composition and excretion rates. We quantified ontogenetic variation in stoichiometry and diet in gizzard shad, Dorosoma cepedianum , an omnivorous fish with a pronounced ontogenetic diet shift; and zebrafish, Danio rerio, grown in the lab with a constant diet. In both species, body stoichiometry varied considerably along the life cycle. Larval gizzard shad and zebrafish had higher molar C:P and N:P ratios than larger fish. Variation in body nutrient ratios was driven mainly by body P, which increased with size. Gizzard shad body calcium content was highly correlated with P content, indicating that ontogenetic P variation is associated with bone formation. Similar trends in body stoichiometry of zebrafish, grown under constant diet in the laboratory, suggest that ontogeny (e.g. bone formation) and not diet shift is the main factor affecting fish body stoichiometry in larval and juvenile stages. The N:P ratio of nutrient excretion also varied ontogenetically in gizzard shad, but the decline from larvae to juveniles appears to be largely associated with variation in the N:P of alternative food resources (zooplankton vs detritus) rather than by fish body N:P. Furthermore, the N:P ratio of larval gizzard shad excretion appears to be driven more by the N:P ratio at which individuals allocate nutrients to growth, more so than static body N:P, further illustrating the need to consider ontogenetic variation. Our results thus show that fish exhibit considerable ontogenetic variation in body stoichiometry, driven by an inherent increase in the relative allocation of P to bones, whereas ontogenetic variation in excretion N:P ratio of gizzard shad is driven more by variation in food N:P than by body N:P.
The central provinces of Argentina are characterized by the presence of a high number of shallow ... more The central provinces of Argentina are characterized by the presence of a high number of shallow lakes, located in endorheic basins, many of which have elevated salinities as well as eutrophic or hypereutrophic condition. The zooplankton of four saline shallow lakes of the province of La Pampa was studied on a monthly basis during a 2-year period to determine its temporal and spatial variation.
... Alberto Pilati,; Wayne. ... In: Daphnia (Eds RHPeters & R.deBernardi) cited in Me... more ... Alberto Pilati,; Wayne. ... In: Daphnia (Eds RHPeters & R.deBernardi) cited in Memorie dell'Istituto Italiano di Idrobiologia, 45, 143192. ... In: A Manual on Methods for the Assessment of Secondary Productivity in Fresh Water (Eds JADowning & FHRigler), pp. ...
Consumers in aquatic food webs can be supported by terrestrial and aquatic primary production. Ho... more Consumers in aquatic food webs can be supported by terrestrial and aquatic primary production. However, we know little about how allochthony, i.e., the proportion of consumer biomass derived from terrestrial organic matter, varies along environmental gradients. Using hydrogen isotopes (deuterium), we quantified allochthony of an ecologically dominant detritivorous fish species (gizzard shad, Dorosoma cepedianum) in reservoir ecosystems, along a gradient of watershed land use (agriculture vs. forest). We predicted that allochthony would decline with an increase in the proportion of watershed land composed of agriculture (% agriculture). This is based on the supposition that as % agriculture increases, so does the export of dissolved inorganic nutrients to lakes, stimulating algal production and reducing the importance of terrestrial organic carbon subsidies. Allochthony accounted for ;34% of gizzard shad production (mean of 11 lakes), although this fraction varied greatly (0-68%) among lakes and isotope mixing model assumptions. Contrary to our hypothesis, we found no relationship between allochthony and % agriculture. However, allochthony was inversely related to total watershed area, as well as the absolute area of the watershed (rather than the percentage) composed of agriculture. We speculate that watershed area and allochthony are negatively correlated because watershed area exerts a strong control on the relative subsidies of dissolved inorganic nutrients vs. particulate organic carbon. Gizzard shad biomass was positively related to phytoplankton primary production but negatively related to allochthony, suggesting that phytodetritus is a higher quality resource than terrestrial detritus. Overall, our results show that both autochthonous and allochthonous carbon fuel the production of this ecologically important detritivore, the relative importance of allochthony decreases with increasing watershed size, and variation in gizzard shad production is closely tied to variation in autochthonous primary production.
Agricultural activities increase exports of nutrients and sediments to lakes, with multiple poten... more Agricultural activities increase exports of nutrients and sediments to lakes, with multiple potential impacts on recipient ecosystems. Nutrient inputs enhance phytoplankton and upper trophic levels, and sediment inputs can shade phytoplankton, interfere with feeding of consumers, and degrade benthic habitats. Allochthonous sediments are also a potential food source for detritivores, as is sedimenting autochthonous phytodetritus, the production of which is stimulated by nutrient inputs. We examined effects of allochthonous nutrient and sediment subsidies on fish and plankton, with special emphasis on gizzard shad (Dorosoma cepedianum). This widespread and abundant omnivorous fish has many impacts on reservoir ecosystems, including negative effects on water quality via nutrient cycling and on fisheries via competition with sportfish. Gizzard shad are most abundant in agriculturally impacted, eutrophic systems; thus, agricultural subsidies may affect reservoir food webs directly and by enhancing gizzard shad biomass. We simulated agricultural subsidies of nutrients and sediment detritus by manipulating dissolved nutrients and allochthonous detritus in a 2 3 2 factorial design in experimental ponds.
Prey quality can have large impacts on the survival, growth and behavior of predators. A number o... more Prey quality can have large impacts on the survival, growth and behavior of predators. A number of studies have examined how different species of prey vary in quality. However, far less is known about intraspecific variation in the quality of prey for predators and even less about what nutrients are extracted from prey by predators. We examined how the sex, feeding level and developmental status of prey affected the quantities of nutrients present in prey bodies and the quantities of nutrients that could be extracted from prey by spiders. Female and well-fed prey were larger and had more nutrients than male and food-limited prey, respectively. After taking into account differences in prey size, spiders extracted relatively more lipid and less protein from female and well-fed prey than from male and food-limited prey, respectively. Mealworms were of higher quality than adult mealworm beetles; spiders were able to extract more lipid, protein and other nutrients from larvae than adults. While lipid present in prey was a good predictor of lipid consumed, protein present in prey was not a reliable predictor of protein consumed. The variation in prey quality that we observed within a single species of prey (i.e. well-fed vs food-limited crickets) was as large as variation in quality among the three species of prey used in these experiments. Intraspecific variation in prey quality may be an important factor affecting predatory arthropods, especially in habitats or at times of year when one species of prey is abundant. Further studies are needed to examine the consequences of intraspecific variation in prey quality on the life history and behavior of predators.
Most stoichiometric models do not consider the importance of ontogenetic changes in body nutrient... more Most stoichiometric models do not consider the importance of ontogenetic changes in body nutrient composition and excretion rates. We quantified ontogenetic variation in stoichiometry and diet in gizzard shad, Dorosoma cepedianum , an omnivorous fish with a pronounced ontogenetic diet shift; and zebrafish, Danio rerio, grown in the lab with a constant diet. In both species, body stoichiometry varied considerably along the life cycle. Larval gizzard shad and zebrafish had higher molar C:P and N:P ratios than larger fish. Variation in body nutrient ratios was driven mainly by body P, which increased with size. Gizzard shad body calcium content was highly correlated with P content, indicating that ontogenetic P variation is associated with bone formation. Similar trends in body stoichiometry of zebrafish, grown under constant diet in the laboratory, suggest that ontogeny (e.g. bone formation) and not diet shift is the main factor affecting fish body stoichiometry in larval and juvenile stages. The N:P ratio of nutrient excretion also varied ontogenetically in gizzard shad, but the decline from larvae to juveniles appears to be largely associated with variation in the N:P of alternative food resources (zooplankton vs detritus) rather than by fish body N:P. Furthermore, the N:P ratio of larval gizzard shad excretion appears to be driven more by the N:P ratio at which individuals allocate nutrients to growth, more so than static body N:P, further illustrating the need to consider ontogenetic variation. Our results thus show that fish exhibit considerable ontogenetic variation in body stoichiometry, driven by an inherent increase in the relative allocation of P to bones, whereas ontogenetic variation in excretion N:P ratio of gizzard shad is driven more by variation in food N:P than by body N:P.
The central provinces of Argentina are characterized by the presence of a high number of shallow ... more The central provinces of Argentina are characterized by the presence of a high number of shallow lakes, located in endorheic basins, many of which have elevated salinities as well as eutrophic or hypereutrophic condition. The zooplankton of four saline shallow lakes of the province of La Pampa was studied on a monthly basis during a 2-year period to determine its temporal and spatial variation.
... Alberto Pilati,; Wayne. ... In: Daphnia (Eds RHPeters & R.deBernardi) cited in Me... more ... Alberto Pilati,; Wayne. ... In: Daphnia (Eds RHPeters & R.deBernardi) cited in Memorie dell'Istituto Italiano di Idrobiologia, 45, 143192. ... In: A Manual on Methods for the Assessment of Secondary Productivity in Fresh Water (Eds JADowning & FHRigler), pp. ...
Consumers in aquatic food webs can be supported by terrestrial and aquatic primary production. Ho... more Consumers in aquatic food webs can be supported by terrestrial and aquatic primary production. However, we know little about how allochthony, i.e., the proportion of consumer biomass derived from terrestrial organic matter, varies along environmental gradients. Using hydrogen isotopes (deuterium), we quantified allochthony of an ecologically dominant detritivorous fish species (gizzard shad, Dorosoma cepedianum) in reservoir ecosystems, along a gradient of watershed land use (agriculture vs. forest). We predicted that allochthony would decline with an increase in the proportion of watershed land composed of agriculture (% agriculture). This is based on the supposition that as % agriculture increases, so does the export of dissolved inorganic nutrients to lakes, stimulating algal production and reducing the importance of terrestrial organic carbon subsidies. Allochthony accounted for ;34% of gizzard shad production (mean of 11 lakes), although this fraction varied greatly (0-68%) among lakes and isotope mixing model assumptions. Contrary to our hypothesis, we found no relationship between allochthony and % agriculture. However, allochthony was inversely related to total watershed area, as well as the absolute area of the watershed (rather than the percentage) composed of agriculture. We speculate that watershed area and allochthony are negatively correlated because watershed area exerts a strong control on the relative subsidies of dissolved inorganic nutrients vs. particulate organic carbon. Gizzard shad biomass was positively related to phytoplankton primary production but negatively related to allochthony, suggesting that phytodetritus is a higher quality resource than terrestrial detritus. Overall, our results show that both autochthonous and allochthonous carbon fuel the production of this ecologically important detritivore, the relative importance of allochthony decreases with increasing watershed size, and variation in gizzard shad production is closely tied to variation in autochthonous primary production.
Agricultural activities increase exports of nutrients and sediments to lakes, with multiple poten... more Agricultural activities increase exports of nutrients and sediments to lakes, with multiple potential impacts on recipient ecosystems. Nutrient inputs enhance phytoplankton and upper trophic levels, and sediment inputs can shade phytoplankton, interfere with feeding of consumers, and degrade benthic habitats. Allochthonous sediments are also a potential food source for detritivores, as is sedimenting autochthonous phytodetritus, the production of which is stimulated by nutrient inputs. We examined effects of allochthonous nutrient and sediment subsidies on fish and plankton, with special emphasis on gizzard shad (Dorosoma cepedianum). This widespread and abundant omnivorous fish has many impacts on reservoir ecosystems, including negative effects on water quality via nutrient cycling and on fisheries via competition with sportfish. Gizzard shad are most abundant in agriculturally impacted, eutrophic systems; thus, agricultural subsidies may affect reservoir food webs directly and by enhancing gizzard shad biomass. We simulated agricultural subsidies of nutrients and sediment detritus by manipulating dissolved nutrients and allochthonous detritus in a 2 3 2 factorial design in experimental ponds.
Prey quality can have large impacts on the survival, growth and behavior of predators. A number o... more Prey quality can have large impacts on the survival, growth and behavior of predators. A number of studies have examined how different species of prey vary in quality. However, far less is known about intraspecific variation in the quality of prey for predators and even less about what nutrients are extracted from prey by predators. We examined how the sex, feeding level and developmental status of prey affected the quantities of nutrients present in prey bodies and the quantities of nutrients that could be extracted from prey by spiders. Female and well-fed prey were larger and had more nutrients than male and food-limited prey, respectively. After taking into account differences in prey size, spiders extracted relatively more lipid and less protein from female and well-fed prey than from male and food-limited prey, respectively. Mealworms were of higher quality than adult mealworm beetles; spiders were able to extract more lipid, protein and other nutrients from larvae than adults. While lipid present in prey was a good predictor of lipid consumed, protein present in prey was not a reliable predictor of protein consumed. The variation in prey quality that we observed within a single species of prey (i.e. well-fed vs food-limited crickets) was as large as variation in quality among the three species of prey used in these experiments. Intraspecific variation in prey quality may be an important factor affecting predatory arthropods, especially in habitats or at times of year when one species of prey is abundant. Further studies are needed to examine the consequences of intraspecific variation in prey quality on the life history and behavior of predators.
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