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The Green Revolution has led to a threefold growth in food production in the last 50 to 75 years, but increases in crop production have required a concurrent increase in [...]

To authenticate to the full-text of this article, please visit this link: http://dx.doi.org/10.1111/j.1600-0706.2009.18596.x Byline: Jotaro Urabe, Shahid Naeem, David Raubenheimer, James J. Elser Author Affiliation: (1)School of Life Sciences, Tohoku Univ., Aoba, Aramaki, Aoba-ku, JP-980-8578 Sendai, Japan (2)Dept of Ecology, Evolution, and Environmental Biology, Columbia Univ. in the City of New York, New York, NY 10027, USA (3)Inst. of Natural Sciences and New Zealand Inst. for Advanced Study, Massey Univ., Albany, New Zealand (4)School of Life Sciences, Arizona State Univ., Tempe, AZ 85287, USA Article History: Paper manuscript accepted 22 December 2009 Article note: J. Urabe, School of Life Sciences, Tohoku Univ., Aoba, Aramaki, Aoba-ku, JP-980-8578 Sendai, Japan. E-mail: urabe@mail.tains.tohoku.ac.jp

Molybdenum (Mo) is essential for the biological assimilation of inorganic nitrogen (N). We compared Mo requirements for [N.sub.2]-fixation in two species of filamentous heterocystous cyanobacteria (HC) to test the hypothesis that coastal HC require higher Mo concentrations than freshwater HC. This expectation follows from the fact that Mo is more concentrated in seawater (~ 105 nmol [L.sup.-1]) than in most freshwaters (< 20 nmol [L.sup.- 1]). Contrary to this hypothesis, we found that both strains maintained [N.sub.2]-fixation for 30 d at 10 nmol [L.sup.-1]. Mo concentrations < 1 nmol [L.sup.-1] induced N-limitation in both species, as indicated by increased C:N ratios and decreased nitrogenase expression and activity. This response took time to induce, likely due to high-affinity molybdate uptake by both species. Measurable [N.sub.2]-fixation persisted in the coastal strain (Nostoc sp. CCMP 2511) for at most 12 d; 3 d were required for chlorophyll a concentrations to fall below those of Mo-replete cultures. An additional 7 d and 11 d, respectively, were required for [N.sub.2]-fixation rates and chlorophyll levels to decline in Molimited freshwater cultures (Nostoc sp. PCC 7120). When Mo was high (> 1 [micro]mol [L.sup.-1]), the freshwater strain exhibited considerable Mo storage (> 100 [micro]mol [mol.sup.-1] Mo:C) whereas cellular Mo remained < 10 [micro]mol [mol.sup.-1] Mo : C in the coastal strain. The high Mo content and extended time required for [N.sub.2]-fixation to decrease in the freshwater strain could be due to expression of the gene mop, which encodes a putative molybdate-storage protein. This study suggests the importance of Mo storage in freshwater HC.

Microbially mediated denitrification is an important process that may ameliorate the effects of nitrogen (N) loading by permanently removing excess N inputs. In this study, we measured the rate of denitrification and nitrous oxide ([N.sub.2]O) production during denitrification in sediments from 32 Norwegian lakes at the high and low ends of a gradient of atmospheric N deposition. Denitrification and [N.sub.2]O production rates averaged 41.7 and 1.1 gmol N*[m.sup.-2]*[h.sup.-1], respectively, for high-deposition lakes. There was no detectable denitrification or [N.sub.2]O production in low-deposition lakes. Epilimnetic nitrate concentration was strongly correlated with denitrification rate ([r.sup.2] = 0.67). We also measured the denitrification rate in response to experimental additions of organic carbon, nitrate, and phosphorus. Experimental nitrate additions stimulated denitrification in sediments of all lakes, regardless of N deposition level. In fact, the rate of denitrification in nitrate-amended treatments was the same magnitude for lakes in both deposition areas. These findings suggest that lake sediments possess considerable capacity to remove nitrate and that this capacity has not been saturated under conditions of chronic N loading. Further, nitrous oxide was nearly 3% of the total gaseous product during denitrification in high-deposition lakes, a fraction that is comparable to polluted marine sediments. Our findings suggest that, while lakes play an important role in N removal in the landscape, they may be a source of [N.sub.2]O emissions, especially in areas subject to elevated N inputs. Key words: atmospheric nitrogen deposition; denitrification; lakes; nitrous oxide; Norway; sediments.

Atmospheric nitrogen (N) deposition to lakes and watersheds has been increasing steadily due to various anthropogenic activities. Because such anthropogenic N is widely distributed, even lakes relatively removed from direct human disturbance are potentially impacted. However, the effects of increased atmospheric N deposition on lakes are not well documented. We examined phytoplankton biomass, the absolute and relative abundance of limiting nutrients (N and phosphorus [P]), and phytoplankton nutrient limitation in alpine lakes of the Rocky Mountains of Colorado (USA) receiving elevated (>6 kg N*[ha.sup.-1] * [yr.sup.-1]) or low ( Key words: alpine lakes; nitrogen; nitrogen deposition; nutrient limitation; phosphorus; phytoplankton; Rocky Mountains, Colorado (USA).

Abstract: As for most other organisms, genome size in zooplankton differs widely. This may have a range of consequences for growth rate, development, and life history strategies, yet the causes [...]

Consumer and resource control of diversity in plant communities have long been treated as alternative hypotheses. However, experimental and theoretical evidence suggests that herbivores and nutrient resources interactively regulate the number and relative abundance of coexisting plant species. Experiments have yielded divergent and often contradictory responses within and among ecosystems, and no effort has to date reconciled this empirical variation within a general framework. Using data from 274 experiments from marine, freshwater, and terrestrial ecosystems, we present a cross-system analysis of producer diversity responses to local manipulations of resource supply and/or herbivory. Effects of herbivory and fertilization on producer richness differed substantially between systems: (i) herbivores reduced species richness in freshwater but tended to increase richness in terrestrial systems; (ii) fertilization increased richness in freshwater systems but reduced richness on land. Fertilization consistently reduced evenness, whereas herbivores increased evenness only in marine and terrestrial ecosystems. Producer community evenness and ecosystem productivity mediated fertilization and herbivore effects on diversity across ecosystems. Herbivores increased producer richness in more productive habitats and in producer assemblages with low evenness. These same assemblages also showed the strongest reduction in richness with fertilization, whereas fertilization increased (and herbivory decreased) richness in producer assemblages with high evenness. Our study indicates that system productivity and producer evenness determine the direction and magnitude of top-down and bottom-up control of diversity and may reconcile divergent empirical results within and among ecosystems. fertilization | herbivory | evenness | species richness | metaanalysis

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.anbehav.2006.02.012 Byline: Susan M. Bertram, John D. Schade, James J. Elser Abstract: Recent findings in the field of ecological stoichiometry indicate that the relationships among key macronutrient elements (e.g. carbon, nitrogen and phosphorus) of organisms and their resources may underlie variation in fitness-conferring behaviours. The amount of phosphorus in an individual's body is often correlated with its rate of growth and reproduction, and low-phosphorus diets are known to reduce growth in a number of insect and crustacean herbivores. These findings suggest that the stoichiometric imbalance between organismal biomass requirements and the relative scarcity of nutrients in nature may underlie variation in condition-dependent behaviours. Here we investigate relationships between body elemental composition and long-distance mate attraction signals produced by male Texas field crickets, Gryllus texensis. Signalling was strongly and positively correlated with the percentage of phosphorus present in the body, but was not correlated with the percentage of carbon or nitrogen present. We also found evidence suggesting that callers and noncalling satellites differ in their elemental composition. To our knowledge, our data are the first to indicate that there may be a relationship between total body phosphorus content and a sexually selected trait. We present a preliminary evaluation of proximate hypotheses to account for the observed patterns. Our results indicate that a stoichiometric perspective may help us to understand the causes of variation in behaviour. Author Affiliation: School of Life Sciences, Arizona State University, U.S.A. Article History: Received 17 February 2005; Revised 28 May 2005; Accepted 27 February 2006 Article Note: (miscellaneous) MS. number: A10095R

The relationship between macronutrient composition of the body and mate attraction signals in Texas field crickets, Gryllus texensis, is analyzed.

Feeding experiments were performed with riverine Bosmina to investigate how their somatic growth rate responded to variation in food resources arising from changing hydrodynamic conditions. Experimental manipulations of food quality and quantity were achieved by diluting riverine suspended particulate matter (seston) to obtain a range of food concentrations and by amending natural seston with laboratory-grown Scenedesmus acutus. Bosmina experienced food limitation during periods of elevated discharge when the P content of seston was low (C : P > 600). Growth rates covaried with body RNA and P contents ([R.sup.2] = 0.96 and 0.86, respectively; content expressed as percent of dry mass), which is consistent with the hypothesis that high growth rates require increased allocation to P-rich ribosomal RNA and that high seston C : P induces P limitation in riverine Bosminza. P limitation arises in riverine consumers of riverine seston when hydrologic conditions favor terrestrial inputs, sediment resuspension, and low algal productivity, thereby resulting in seston fractions dominated by P-poor materials. During low discharge, riverine seston was P-rich relative to Bosmina requirements and growth rates were decoupled from body P content. Bosmina RNA content was strongly and linearly related to growth over a broad range of resource conditions, suggesting that it may be a useful surrogate to assess dietary sufficiency of food resources in natural settings.

Abstract. Nutritional imbalances are of great interest in the ecological stoichiometry literature, in which researchers have focused almost exclusively on cases where nutrients are available in low amounts relative to energy (carbon), and animal growth is impaired due to insufficient nutrient intake. Little attention has been given to situations where food elemental content is higher than the level that satisfies animal requirements. However, most animals are strongly homeostatic with respect to the elemental composition of their body; hence they must excrete the excess of elements that are not in short supply. To date, stoichiometric theory has assumed that excretion of superfluous elements does not come with a cost and, thus, that consumption of food with surplus nutrients does not impair performance. Here we challenge this assumption, based on a compilation of several examples involving food phosphorus content that show that the performance of a wide variety of animals decreases when supplied with food containing high concentrations of (potentially) limiting nutrients. We discuss possible mechanisms for this phenomenon, and suggest that animals most vulnerable to effects of high food nutrient content are those that normally feed on low- quality (low-nutrient: C) food, and have a relatively low body nutrient content themselves, such as herbivores and detritivores. Key words: high-P food; nutritional imbalance; stoichiometry theory; superfluous nutrients affect animal performance; threshold elemental ratio.

The Cuatro Cienegas basin in the Chihuahuan desert is a system of springs, streams, and pools. These ecosystems support >70 endemic species and abundant living stromatolites and other microbial communities, representing a desert oasis of high biodiversity. Here, we combine data from molecular microbiology and geology to document the microbial biodiversity of this unique environment. Ten water samples from locations within the Cuatro Cienegas basin and two neighboring valleys as well as three samples of wet sediments were analyzed. The phylogeny of prokaryotic populations in the samples was determined by characterizing cultured organisms and by PCR amplification and sequencing of 16S rRNA genes from total community DNA. The composition of microbial communities was also assessed by determining profiles of terminal restriction site polymorphisms of 16S rRNA genes in total community DNA. There were 250 different phylotypes among the 350 cultivated strains. Ninety-eight partial 16S rRNA gene sequences were obtained and classified. The clones represented 38 unique phylotypes from ten major lineages of Bacteria and one of Archaea. Unexpectedly, 50% of the phylotypes were most closely related to marine taxa, even though these environments have not been in contact with the ocean for tens of millions of years. Furthermore, terminal restriction site polymorphism profiles and geological data suggest that the aquatic ecosystems of Cuatro Cienegas are hydrologically interconnected with adjacent valleys recently targeted for agricultural intensification. The findings underscore the conservation value of desert aquatic ecosystems and the urgent need for study and preservation of freshwater microbial communities. Cuatro Cienegas | terminal restriction site polymorphism | 16S clone library | water conservation | microbial ecology

Understanding the storage, flux, and turnover of nutrients in organisms is important for quantifying contributions of biota to biogeochemical cycles. Here we present a model that predicts the storage of phosphorus-rich RNA and whole-body phosphorus content in eukaryotes based on the mass- and temperature-dependence of ATP production in mitochondria. Data from a broad assortment of eukaryotes support the model's two main predictions. First, whole-body RNA concentration is proportional to mitochondrial density and consequently scales with body mass to the--1/4 power. Second, whole-body phosphorus content declines with increasing body mass in eukaryotic unicells but approaches a relatively constant value in large multicellular animals because the fraction of phosphorus in RNA decreases relative to the fraction in other pools. Extension of the model shows that differences in the flux of RNA-associated phosphorus are due to the size dependencies of metabolic rate and RNA concentration. Thus, the model explicitly links two biological currencies at the individual level: energy in the form of ATP and materials in the form of phosphorus, both of which are critical to the functioning of ecosystems. The model provides a framework for linking attributes of individuals to the storage and flux of phosphorus in ecosystems. growth rate hypothesis | metabolic theory of ecology | stoichiometry | allometry

The growth rate hypothesis (GRH) proposes that variation in organismal C : N : P ratios is associated with growth rate due to differential allocation to P-rich ribosomal RNA to support growth. A further extension of the GRH proposes that this variation is associated with the structure of ribosomal (r)DNA genes (e.g., promoter-enhancer sequences in the rDNA intergenic spacer [IGS]) that influence the production rate of rRNA. To test these ideas, we examined growth rate, rDNA structure, RNA : DNA ratios, and elemental composition (C : N : P) in multiple clones of three Daphnia species (pulex, pulicaria, magna) in controlled laboratory experiments. Results show that a portion of the rDNA motif, consisting primarily of the IGS, shows considerable interspecific and intraspecific length variation. Significant interspecific differences in all parameters were found, while significant intraspecific (clone) effects were detected only for RNA : DNA ratios and growth rate. As predicted by the GRH, there were significant positive correlations between RNA : DNA ratio and either growth rate or rDNA/IGS length, and a significant positive correlation between rDNA/IGS length and growth rate, when clonal means for all three species were examined. However, no clear-cut relationships between RNA : DNA and either C : P or N : P were observed for any of the three species. Likewise, no discernible intraspecific relationships between growth rate and either C : P or N : P were detected. These preliminary findings suggest that further study of elemental composition, nucleic acid content, and growth rates of organisms may lead to a clearer understanding of the role of stoichiometric constraints in influencing the ecology and evolution of natural populations.

Whereas it is acknowledged that the C:N:P stoichiometry of consumers and their resources affects both the structure and the function of food webs, and eventually influences broad-scale processes such as global carbon cycles, the mechanistic basis for the variation in stoichiometry has not yet been fully explored. Empirical evidence shows that the specific growth rate is positively related to RNA concentration both between and within taxa in both unicellular and multicellular organisms. Since RNA is rich in P and constitutes a substantial part of the total P in organisms, a high growth rate is also connected with a high P content. We argue that the reason for this pattern is that the growth of all biota is closely linked with their protein synthesis rate, and thus with the concentration of ribosomal RNA. Dynamic energy budget theory supports the positive relationship between RNA and specific growth rate in microorganisms, whereas the predictions concerning multicellulars only partially agrees with the observed pattern. In a simple model of consumer growth, we explore the consequences of various allocation patterns of RNA, protein, carbohydrates/lipids, and other biochemical constituents on organism potential growth rate and C:N:P stoichiometry. According to the model the percentage of N and especially percentage of P per dry mass increases with increasing specific growth rate. Furthermore, the model suggests that macromolecule allocation patterns and thus N:P stoichiometry are allowed to differ substantially at low growth rates whereas the stoichiometry at high growth rates is much more constricted at low N:P. The model fits empirical data reasonably well, but it is also acknowledged that complex life cycles and associated physiological constraints may result in other patterns. We also use a similar approach of modeling organism growth from basic biochemical principles to illustrate fundamental connections among biochemical allocation and C:N stoichiometry in autotroph production, which is based on allocation patterns between carbohydrates and rubisco. Similar to the RNA-protein model, macromolecular composition and C:N ratios are more constrained at high than at low growth rates. The models and the empirical data together suggest that organism growth is tightly linked with the organisms' biochemical and elemental composition. The stoichiometry of growth impinges on nutrient cycles and carbon fluxes at the ecosystem level. Thus, focus on the biological basis of organism C:N:P stoichiometry can mechanistically connect growth strategy and biochemical and cellular mechanisms of biota to major ecological consequences. Key words: autotroph production; C:N:P stoichiometry; consumer growth rate; dynamic energy budget theory; macromolecular allocation patterns; protein allocation; ribosomal RNA; rubisco.

The fate of carbon (C) in organisms, food webs, and ecosystems is to a major extent regulated by mass-balance principles and the availability of other key nutrient elements. In relative terms, nutrient limitation implies excess C, yet the fate of this C may be quite different in autotrophs and heterotrophs. For autotrophs nutrient limitation means less fixation of inorganic C or excretion of organic C, while for heterotrophs nutrient limitation means that more of ingested C will 'go to waste' in the form of egestion or respiration. There is in general a mismatch between autotrophs and decomposers that have flexible but generally high C:element ratios, and consumers that have lower C:element ratios and tighter stoichiometric regulation. Thus, C-use efficiency in food webs may be governed by the element ratios in autotroph biomass and tend to increase when C:element ratios in food approach those of consumers. This tendency has a strong bearing on the sequestration of C in ecosystems, since more C will be diverted to detritus entering soils or sediments when C-use efficiency is low due to stoichiometric imbalance. There will be a strong evolutionary pressure to utilize such excess C for structural and metabolic purposes. This article explores how these basic principles may regulate C sequestration on different scales in aquatic and terrestrial ecosystems. Key words: carbon; C sequestration; ecosystems; C-use efficiency; grazing; nitrogen; phosphorus; stoichiometry, role in carbon sequestration.

The growth rate hypothesis (GRH) proposes that variation in organism C:P and N:P ratios reflects variation in P content associated with altered allocation to P-rich ribosomal RNA under different growth rates. We tested the GRH by examining the effects of food quantity and stoichiometric quality (differing carbon : nitrogen : phosphorus [C:N:P] ratios) on juvenile growth and chemical composition (C:N:P, RNA, and DNA contents) of two species of Daphnia (D. galeata, D. pulicaria). Daphnia in P-limited experiments were fed saturating and limiting concentrations of food (Scenedesmus acutus) of high P (C:P = 110 [+ or -] 7.3), medium P (456 [+ or -] 20.7), and low P (934 [+ or -] 23.6), and in an N-limited experiment D. pulicaria was fed saturating concentrations of high N (C:N = 6.31 [+ or -] 0.35), medium 1 and medium 2 (9.0 [+ or -] 0.42; 15.0 [+ or -] 0.49, respectively), and low N (18.22 [+ or -] 0.56) food. In Plimited experiments, both Daphnia species grew fastest under P-rich, high food conditions and grew slowest under P-deficient, low food conditions, showing effects of both food quality and quantity. Daphnia body percentage P, C:P, N:P, and percentage RNA were tightly correlated with growth rates, and RNA contributed a significant fraction of total body P (48.8% [[+ or -] 2.0%]). This strong three-way (growth-RNA-P) set of correlations supports the GRH. In the N-limited experiment, food C:N had a moderate effect on Daphnia growth. While there was a good linear correlation between P and RNA, growth rate was uncorrelated with RNA content and P content, suggesting that the three-way coupling of growth, RNA, and P content is broken under N limitation of growth, but more data for these conditions are needed. These data help in delineating the physiological conditions under which the GRH holds and may be useful in interpreting variation in body stoichiometry of zooplankton from field and lab studies.

Biological stoichiometry is the study of the balance of energy and multiple chemical elements in biological systems. A key idea in biological stoichiometry is the growth rate hypothesis, which states [...]

Phytoplankton growth and elemental composition are influenced by a number of factors such as photosynthetically active radiation (PAR) and nutrient availability. However, little is known about the influence of solar ultraviolet radiation (UVR) and interactions with nutrients on algal growth processes in situ. We tested the effects of solar radiation and phosphorus supply on algal growth kinetics and elemental composition in two boreal lakes (northwestern Ontario, Canada) during summer 1999. Growth bioassays (at five phosphorus concentrations) assessed changes in algal growth and elemental composition exposed to (1) ultraviolet A [UVA], ultraviolet B [UVB], and photosynthetically active radiation [PAR], (2) UVA and PAR, and (3) PAR only. Growth rates, calculated from changes in seston carbon and chlorophyll, responded strongly to both P and UVR. Results indicated that phytoplankton growth was co-regulated by P limitation and UVR suppression, with highest growth rates found in high P, low UVR treatments. Phytoplankton exposed to both UVA and UVB generally grew more slowly than those exposed to PAR only, even at high P levels. UVB and UVA reduced maximum growth rates by 8-66% and 11-21%, respectively. Phytoplankton growth was more strongly affected by UVB in spring than later in summer, possibly due to shifts in the dominant species present. Manipulations of light and P supply both significantly affected seston C:P ratios. UVR reduced sestonic C:P. Such changes in growth rates and C:P ratios from UVR exposure may have important implications for pelagic food web dynamics. Key words: C:P ratio; Canada, northwestern Ontario; elemental composition; growth kinetics; lakes, boreal; multiple stressors; phosphorus limitation; photosynthetically active radiation; phytoplankton growth; ultraviolet radiation.

Biogeochemical PCB cycling of PCB in lakes of different trophic status has been studied in a paired-lake experiment that used two remote, atmospherically driven lakes in the Experimental Lakes Area. The goal was to find out more about the stresses of trophic condition on air-water exchange and settling fluxes of PCBs. Hypothetically, eutrophic lakes would have access to the same PCB concentrations in the atmosphere as oligotrophic lakes and would gain more chemical mass through better air-water exchange. Net volatilization dominated in the ice-free period. Mass budgets indicate that the likely major PCB input was from the watershed. Results show intimate linkage of land, atmospheric and aquatic reservoirs of PCBs.

Ecosystem science and evolutionary biology have long been infrequent and uncomfortable bedfellows (Hagen 1992, Holt 1995, McIntosh 1985). However, the convergence of a global decline in biodiversity and global alterations [...]

Stocking of the dominant planktivore of Castle Lake (rainbow trout) was discontinued to examine the impact of food web interactions on zooplankton communities and inter- and intra-annual dynamics of ecosystem properties (light penetration, primary productivity). Dynamics of zooplankton and ecosystem processes were examined for 3 yr following the manipulation and compared to 2-3 yr of premanipulation data. Sampling of vertebrate and invertebrate planktivores documented shifts in other members of the zooplanktivore guild as rainbow trout declined. Reduction of rainbow trout densities led to compensatory responses in other components of the Castle Lake fish assemblage as brook trout and golden shiners increased in abundance. This compensation resulted in increased rates of vertebrate planktivory on daphnids within 2 yr after trout stocking was discontinued. Zooplankton shifts in response to discontinuance of trout stocking were more rapid, particularly an immediate increase in a previously rare invertebrate predator (Diacyclops thomasi). Other limnological parameters also responded rapidly following the manipulation: water transparency declined and primary productivity (PPr) increased. In addition, intra-annual patterns (i.e., seasonal development) and the vertical distribution (shallow vs. deep) of PPr appeared to be affected by the food web manipulation. Our results indicate that complexities of real food webs complicate the prediction of the outcome of food web perturbations. Reduction of the previously dominant planktivore (rainbow trout) led to increases in other zooplanktivores (Diacyclops, golden shiners, brook trout) that resulted in enhanced predation pressure on zooplankton herbivores. Our results also indicate that alterations in water quality parameters (transparency, PPr) in response to food web alterations need not necessarily be mediated through changes in the abundance of Daphnia, as strong limnological responses preceded reductions in Daphnia by a year. We hypothesize an alternative mechanism for food-web-induced changes in lake ecosystem dynamics: changes in water clarity and productivity can result when cyclopoid predation strongly affects micrograzers. Key words: cascading trophic interactions; ecosystem variability; food web compensation; lake food webs; primary productivity., INTRODUCTION The idea of 'Cascading Trophic Interactions' (or CTI; Carpenter et al. 1985) has provided a conceptual framework for understanding the impact of higher trophic levels on ecosystem dynamics. Since [...]

To meet our demands for energy, humankind has moved masses of carbon from deep underground into the atmosphere, wreaking havoc with the climate. To meet our demand for food, we [...]

During summer 1987, a series of experiments was performed in conjunction with monitoring of in situ plankton dynamics in nutrient-deficient Castle Lake, California. These factorial manipulations of nutrients and zooplankton were designed to separate the direct (grazing mortality) and indirect (stimulation of algal growth by nutrient recycling) effects of grazers on both species-specific phytoplankton dynamics, as well as aggregate properties such as total biomass, productivity, and biomass turnover. Grazing loss rates differed significantly among algal species with the mean grazing loss rate suffered by an algal species a negative function of cell or colony size. Stimulation of division rates in the presence of zooplankton (compared to an unenriched treatment lacking zooplankton) was commonly observed. Nutrient and grazer treatments also had significant impacts on algal biomass (indicated by chlorophyll concentration), productivity (PPR), and PPR/chlorophyll, and significant nutrient-grazer interactions were frequently observed. Species-specific algal responses to grazers were aggregated across the phytoplankton by weighting species-specific parameters by the contribution of each species to total community biomass in order to provide community-wide estimates of the importance of direct and indirect effects on algal dynamics. Finally, linkages between population-level responses and aggregate properties were demonstrated by examining relationships between total phytoplankton biovolume concentration and chlorophyll concentration in various treatments, by comparing community-wide grazing rates estimated from aggregated species-specific grazing rates and from changes in chlorophyll growth rates, and by relating the aggregated degree of species-specific growth stimulation to stimulation of biomass turnover. These results indicate that phytoplankton responses to grazers in Castle Lake reflect a mix of direct and indirect effects that varies considerably both between species and through time during the stratified season. Keywords: herbivory; indirect effects; mesocosms; nutrients; phytoplankton; zooplankton.

Human activities have more than doubled the amount of nitrogen (N) circulating in the biosphere. One major pathway of this anthropogenic N input into ecosystems has been increased regional deposition from the atmosphere. Here we show that atmospheric N deposition increased the stoichiometric ratio of N and phosphorus (P) in lakes in Norway, Sweden, and Colorado, United States, and, as a result, patterns of ecoLogicaL nutrient Limitation were shifted. Under low N deposition, phytoplankton growth is generally N-limited; however, in high-N deposition lakes, phytoplankton growth is consistently P-limited. Continued anthropogenic amplification of the global N cycle will further alter ecological processes, such as biogeochemical cycling, trophic dynamics, and biological diversity, in the world's lakes, even in lakes far from direct human disturbance. 10.1126/science.1176199

Ecology is a leading discipline in the synthesis of diverse knowledge. Ecologists have had considerable experience in bringing together diverse, multinational data sets, disciplines, and cultural perspectives to address a […]

Author(s): James J. Elser (corresponding author) [1]; William F. Fagan [1]; Robert F. Denno [2]; Dean R. Dobberfuhl [1, 3]; Ayoola Folarin [1]; Andrea Huberty [2]; Sebastian Interlandi [4]; Susan [...]

A study of nutrient ratios in pelagic ecosystems in freshwater and marine habitats reveals that the ecological stoichiometry of the zooplankton- phytoplankton interaction varies qualitatively in marine and freshwater ecosystems. The N/P ratio of phytoplankton is higher in lakes than in seawater, but that of zooplankton is higher in marine sites than in freshwater. The qualitative difference results in varying mechanics of food quality and nutrient recycling of the zooplankton-phytoplankton medium in lakes and oceans.

A review to integrate information about structural and functional aspects of rDNA that impact the ecology and evolution of organisms is presented. There are strong reciprocal feedbacks between rDNA and the ecology of all organisms mediated through increased phosphorous demand in organisms with high rRNA content.

An experiment to investigate the relationships between food quantity, quality, individual and population growth was undertaken under realistic field conditions in a Canadian shield lake with high seston carbon (C) and phosphorus (P) ratios on herbivorous Daphnia dentifera. Results revile that the direct effects of P-limited food on individual growth inhibit the population development of Daphnia.

Laboratory studies are increasingly indicating that the quality of nutrientlimited algae is suboptimal for zooplankton production. However, little is known about how quality is affected by nutrient limitation of phytoplankton in more natural situations. To test for phosphorus (P) limitation of zooplankton growth under realistic food conditions, we performed a set of 5-d experiments using Daphnia dentifera and suspended particulate matter (seston) from three lakes at the Experimental Lakes Area (Ontario, Canada). Neonate Daphnia fed for 6 h per day on freshly collected seston enriched or unenriched with [PO.sub.4] and spent the rest of the day feeding on unaltered natural seston. [PO.sub.4] enrichment did not affect food abundance or concentrations and composition of essential fatty acids but dramatically lowered seston C:P ratio and significantly stimulated Daphnia growth. These results demonstrate that, even with field-collected seston, the effects of algal phosphorus limitation can extend to herbivores through reduced food quality. Key words: C:P ratio; Daphnia dentifera; Daphnia growth vs. P availability in food; Experimental Lakes Area (Ontario, Canada); fatty acids; food quality; nutrient limitation; phosphorus limitation and food quality; zooplankton.

Physiological Ecology: How Animals Process Energy, Nutrients, and Toxins. William H. Karasov and Carlos Martinez del Rio. Princeton University Press, Princeton, NJ, 2007. 744 pp., illus. $65.00 (ISBN 9780691074535 cloth). [...]

Ecologists are increasingly recognizing the importance of consumers in regulating ecosystem processes such as nutrient cycling. Ecologists have recently made considerable progress in understanding nutrient cycling and trophic interactions in pelagic systems by application of a new concept, ecological stoichiometry, to consumer-driven processes. In this paper we synthesize these conceptual advances within pelagic ecology and attempt to illustrate how they may be usefully applied in other ecosystems. Stoichiometric theory shows that both grazer and algal elemental composition are critical parameters influencing rates and ratios of nutrient release. Thus, the stoichiometry of nutrient recycling is a feedback mechanism linking grazer dynamics and algal nutritional status. Incorporation of such effects into a fully dynamic stoichiometric model generates profound changes in the predicted dynamics of algae and grazers, suggesting that adoption of a stoichiometric view may substantively alter our view of the interaction between trophic dynamics and nutrient cycling. The basic predictions of stoichiometric models of nutrient release are generally supported by experimental data showing that N:P release ratios are primarily a function of algal N:P ratio and secondarily a function of grazer N:P ratio, and that rates of P release by grazers are also related to food P:C. Furthermore, evidence for effects of nutrient release stoichiometry on phytoplankton communities and pelagic ecosystem function is accumulating, including data showing consistent alterations in algal physiological status and ecosystem-scale changes in N fixation in response to altered grazer community structure and elemental composition. As the general features of the stoichiometry of algae-zooplankton interactions reflect fundamental biological processes linked to plant and animal mineral nutrition, the stoichiometric view of consumer-driven nutrient recycling can easily be applied to other ecosystems, including terrestrial and benthic food webs. A suite of potential applications of stoichiometric thinking to benthic and terrestrial habitats is suggested. Key words: carbon; consumer-driven nutrient recycling; food quality; nitrogen; nutrient cycling; phosphorus; stoichiometry; zooplankton., INTRODUCTION Ecological stoichiometry is an approach that analyzes the constraints and consequences of mass balance of multiple chemical elements in ecological interactions (Sterner 1995, Elser et al. 1996, Hessen 1997). [...]