Ecological Stoichiometry

Nitrogen (N) and phosphorus (P) and N: P ratio in terrestrial plants and the patterns at a large geographical scale are an important issue in ecological stoichiometry. In particular, it is essential to know that for a single species, how the N: P stoichiometry varies with climatic ...

Intraspecific variation in body pigmentation is an ecologically and evolutionary important trait; however, the pigmentation related trade-offs in marine zooplankton are poorly understood. We tested the effects of intrapopulation phenotypic variation in the pigmentation of the copepod Eurytemora affinis on predation risk, foraging, growth, metabolic activity and antioxidant capacity. Using pigmented and unpigmented specimens, we compared (1) predation and selectivity by the invertebrate predator Cercopagis pengoi, (2) feeding activity of the copepods measured as grazing rate in experiments and gut fluorescence in situ, (3) metabolic activity assayed as RNA:DNA ratio in both experimental and field-collected copepods, (4) reproductive output estimated as egg ratio in the population, and (5) total antioxidant capacity. Moreover, mitochondrial DNA (mtDNA) COI gene variation was analysed. The pigmented individuals were at higher predation risk as evidenced by significantly higher predation rate by C. pengoi on pigmented individuals and positive selection by the predator fed pigmented and unpigmented copepods in a mixture. However, the antioxidant capacity, RNA:DNA and egg ratio values were significantly higher in the pigmented copepods, whereas neither feeding rate nor gut fluorescence differed between the pigmented and unpigmented copepods. The phenotypic variation in pigmentation was not associated with any specific mtDNA genotype. Together, these results support the metabolic stimulation hypothesis to explain variation in E. affinis pigmentation, which translates into beneficial increase in growth via enhanced metabolism and antioxidant protective capacity, together with disadvantageous increase in predation risk. We also suggest an alternative mechanism for the metabolic stimulation via elevated antioxidant levels as a primary means of increasing metabolism without the increase in heat absorbance. The observed trade-offs are relevant to evolutionary mechanisms underlying plasticity and adaptation and have the capacity to modify strength of complex trophic interactions. Citation: Gorokhova E, Lehtiniemi M, Motwani NH (2013) Trade-Offs between Predation Risk and Growth Benefits in the Copepod Eurytemora affinis with Contrasting Pigmentation. PLoS ONE 8(8): e71385.

Biological and environmental contrasts between aquatic and terrestrial systems have hindered analyses of community and ecosystem structure across Earth's diverse habitats. Ecological stoichiometry provides an integrative approach for such analyses, as all organisms are composed of the same major elements (C, N, P) whose balance affects production, nutrient cycling, and food-web dynamics. Here we show both similarities and differences in the C:N:P ratios of primary producers (autotrophs) and invertebrate primary consumers (herbivores) across habitats. Terrestrial food webs are built on an extremely nutrient-poor autotroph base with C:P and C:N ratios higher than in lake particulate matter, although the N:P ratios are nearly identical. Terrestrial herbivores (insects) and their freshwater counterparts (zooplankton) are nutrient-rich and indistinguishable in C:N:P stoichiometry. In both lakes and terrestrial systems, herbivores should have low growth efficiencies (10-30%) when cons...

1The science of nutritional ecology spans a wide range of fields, including ecology, nutrition, behaviour, morphology, physiology, life history and evolutionary biology. But does nutritional ecology have a unique theoretical framework and research program and thus qualify as a field of research in its own right?2We suggest that the distinctive feature of nutritional ecology is its integrative nature, and that the field would benefit from more attention to formalizing a theoretical and quantitative framework for developing this.3Such a framework, we propose, should satisfy three minimal requirements: it should be nutritionally explicit, organismally explicit, and ecologically explicit.4We evaluate against these criteria four existing frameworks (Optimal Foraging Theory, Classical Insect Nutritional Ecology, the Geometric Framework for nutrition, and Ecological Stoichiometry), and conclude that each needs development with respect to at least one criterion.5We end with an initial attempt at assessing the expansion of our own contribution, the Geometric Framework, to better satisfy the criterion of ecological explicitness.The science of nutritional ecology spans a wide range of fields, including ecology, nutrition, behaviour, morphology, physiology, life history and evolutionary biology. But does nutritional ecology have a unique theoretical framework and research program and thus qualify as a field of research in its own right?We suggest that the distinctive feature of nutritional ecology is its integrative nature, and that the field would benefit from more attention to formalizing a theoretical and quantitative framework for developing this.Such a framework, we propose, should satisfy three minimal requirements: it should be nutritionally explicit, organismally explicit, and ecologically explicit.We evaluate against these criteria four existing frameworks (Optimal Foraging Theory, Classical Insect Nutritional Ecology, the Geometric Framework for nutrition, and Ecological Stoichiometry), and conclude that each needs development with respect to at least one criterion.We end with an initial attempt at assessing the expansion of our own contribution, the Geometric Framework, to better satisfy the criterion of ecological explicitness.

In the Mediterranean area, the simultaneous occurrence of pedological, climatic and economic constraints often sets a limit on the profitability of agriculture, and farmers are forced to grow a reduced number of species, dealing with a secure-albeit low-market income. The introduction of medicinal and aromatic plants (MAPs) inside the current farming systems could represent a useful means to meet the multifunctional role of agriculture: producing safe food, in respect of the environment, and contributing to the development of rural areas. The study of the relationships between MAPs and the soils in which they may be grown may have two approaches: (1) the evaluation of yield and qualitative response of MAPs to the variation of soil features; and (2) the study of selective recovery of certain elements (toxic and beneficial), and their subsequent release in herbal products. In many MAPs, significant variations of plant characteristics have been ascertained with varying soil traits, and...

1. Protein quantification is a routine procedure in ecological studies despite the inherent limitations of well‐acknowledged protein determination methods which have been largely overlooked by ecologists. Thus, we want to bridge this knowledge gap, in hopes of improving the way ecologists quantify proteins and interpret findings.
2. We surveyed the ecological literature to determine how and why ecologists quantify proteins. To determine whether different quantification methods produce comparable results across taxa, and between populations of a single species, we estimated the protein content of eight phylogenetically diverse taxa, and of desert isopods fed different diets, using various derived protocols of the 'crude protein', Bradford and BCA methods.
3. We found that ecologists use many protein quantification procedures, often without reporting the crucial information needed to evaluate and repeat their methods. Our empirical work demonstrated that the three quantification methods examined, and their derived protocols, resulted in highly divergent protein estimations that were inconsistent in rank across taxa, preventing conversion between methods. We also found that different quantification methods yielded different answers to whether isopod protein content is affected by diet.
4. We conclude that commonly used quantification techniques yield distinct protein estimations with varying precision, and no single method is likely to be more accurate than another across taxa which may lead to inconsistent results across taxa and between conspecifics. Inaccurate protein quantification may explain the observed mismatch between organismal N and protein that has plagued some recent studies and that contradicts the principles of ecological stoichiometry. We recommend using a single BCA protocol to reduce inconsistencies across studies, until the promising Amino Acid Analysis becomes more affordable, accurate, and accessible to ecologists. Until then, ecologists should consider the above‐mentioned drawbacks of protein quantification methods and interpret their results accordingly.

Aquatic plants fulfil a wide range of ecological roles, and make a substantial contribution to the structure, function and service provision of aquatic ecosystems. Given their well-documented importance in aquatic ecosystems, research into aquatic plants continues to blossom. The 14th International Symposium on Aquatic Plants, held in Edinburgh in September 2015, brought together 120 delegates from 28 countries and six continents. This special issue of Hydrobiologia includes a select number of papers on aspects of aquatic plants, covering a wide range of species, systems and issues. In this paper, we present an overview of current trends and future directions in aquatic plant research in the early twenty first century. Our understanding of aquatic plant biology, the range of scientific issues being addressed and the range of techniques available to researchers have all arguably never been greater; however, substantial challenges exist to the conservation and management of both aquatic plants and the ecosystems in which they are found. The range of countries and continents represented by conference delegates and authors of papers in the special issue illustrates the global relevance of aquatic plant research in the early twenty first century but also the many challenges that this burgeoning scientific discipline must address.

Many factors, such as rising sea levels and human alterations, threaten coastal wetlands in the United States and around the world. To reverse some wetland loss, dredge material, tidal flow, or river flow can be used to create new wetlands or existing wetlands can be managed to increase plant productivity. Identifying the causes of limited production can improve management plans by suggesting possible remedies. Managing and restoring marshes depends on understanding which stress factors limit growth of key marsh-building plants. Spartina patens is a common marsh-building species of grass in brackish marshes along the Gulf of Mexico and Atlantic coasts of North America and it is often the target of management and restoration plans. S. patens was grown under six flooding levels in a field experiment. S. patens plants grown at lower elevations had consistently lower biomass, in contrast to S. alterniflora, which has been shown to exhibit peak biomass at intermediate levels of flooding. Critical values of elemental concentrations in plant tissue are widely used to diagnose mineral deficiencies in agricultural crops and are just beginning to be developed aid wetland management and restoration. For leaf tissue harvested in summer, [Mn] < 256 ppm and [Ca] < 0.3% indicated that plants grew at lower elevations and had limited biomass. The results suggest that concentrations of Mn and Ca in the leaf tissue of S. patens could form part of an indicator to monitor below-ground productivity of marshes. Although low concentrations of these elements were associated with the smaller root and shoot biomass of plants grown at low elevations, variability in the relationship suggests that additional factors may need to be considered. Marsh managers should monitor soil elevation loss carefully if they choose to drain marshes to increase plant production to prevent excessive loss of soil elevation.

A fundamental goal of ecological network research is to understand how the complexity observed in nature can persist and how this affects ecosystem functioning. This is essential for us to be able to predict, and eventually mitigate, the consequences of increasing environmental perturbations such as habitat loss, climate change, and invasions of exotic species. 2. Ecological networks can be subdivided into three broad types: 'traditional' food webs, mutualistic networks and host-parasitoid networks. There is a recent trend towards cross-comparisons among network types and also to take a more mechanistic, as opposed to phenomenological, perspective. For example, analysis of network configurations, such as compartments, allows us to explore the role of co-evolution in structuring mutualistic networks and host-parasitoid networks, and of body size in food webs. 3. Research into ecological networks has recently undergone a renaissance, leading to the production of a new catalogue of evermore complete, taxonomically resolved, and quantitative data. Novel topological patterns have been unearthed and it is increasingly evident that it is the distribution of interaction strengths and the configuration of complexity, rather than just its magnitude, that governs network stability and structure. 4. Another significant advance is the growing recognition of the importance of individual traits and behaviour: interactions, after all, occur between individuals. The new generation of high-quality networks is now enabling us to move away from describing networks based on species-averaged data and to start exploring patterns based on individuals. Such refinements will enable us to address more general ecological questions relating to foraging theory and the recent metabolic theory of ecology. 5. We conclude by suggesting a number of 'dead ends' and 'fruitful avenues' for future research into ecological networks.

1. Animals can mitigate the consequences of conflicting food-web constraints (e.g. resource availability vs. predation risk) through plasticity in the expression of functional traits. Because functional trait expression in turn determines a species' impact on ecosystem functions, e.g. its trophic function, there is a growing need to develop a predictive theory that links trait plasticity to ecosystem functioning. But there is currently an incomplete empirical foundation on which to develop such theory. 2. To address this issue, we explored the link between plasticity in a suite of traits (e.g. head morphology, gut size, bite size) that determine the trophic function of a generalist grasshopper herbivore facing predation risk. We reared grasshoppers in the field under two single-forage environments where the plant resources had different physical and nutritional properties and in intermediate mixed-forage environments with or without risk of spider predation. 3. We found that in the single-forage environments, grasshoppers became more efficient at ingesting the resource they were reared on. 4. In mixed-resource environments, grasshoppers developed a phenotype that was not intermediate to the phenotypes in the two single-forage environments, regardless of predation risk. 5. We propose that the suite of phenotypic changes observed in our study represent two alternative feeding strategies that vary with the possibility of using behavioural resource selection in different environmental contexts. 6. Our results suggest that plasticity in trophic function may not emerge from a direct link between the primary traits that determine consumer consumption efficiency given the physical properties of its resources (as is customarily presumed) but rather indirectly from secondary traits that may remain latent until such time that they are drawn into play when the species faces a particular challenge. This means that fully understanding how functional traits influence a species' role in an ecosystem requires consideration of a broader suite of traits than simply those assumed to constrain resource ingestion.

The factors regulating the structure of food webs are a central focus of community and ecosystem ecology, as trophic interactions among species have important impacts on nutrient storage and cycling in many ecosystems. For soil invertebrates in grassland ecosystems in the Netherlands, the site-specific slopes of the faunal biomass to organism body mass relationships reflected basic biochemical and biogeochemical processes associated with soil acidity and soil C : N : P stoichiometry. That is, the higher the phosphorus availability in the soil, the higher, on average, the slope of the faunal biomass size spectrum (i.e., the higher the biomass of large-bodied invertebrates relative to the biomass of small invertebrates). While other factors may also be involved, these results are consistent with the growth rate hypothesis from biological stoichiometry that relates phosphorus demands to ribosomal RNA and protein production. Thus our data represent the first time that ecosystem phosphorus availability has been associated with allometry in soil food webs (supporting information available online). Our results have broad implications, as soil invertebrates of different size have different effects on soil processes.

Diatoms and dinoflagellates are major bloomforming
phytoplankton groups competing for resources in
the oceans and coastal seas. Recent evidence suggests that
their competition is significantly affected by climatic factors
under ongoing change, modifying especially the conditions
for cold-water, spring bloom communities in temperate
and Arctic regions. We investigated the effects of phytoplankton
community composition on spring bloom carbon
flows and nutrient stoichiometry in multiyear mesocosm
experiments. Comparison of differing communities showed
that community structure significantly affected C accumulation
parameters, with highest particulate organic carbon
(POC) buildup and dissolved organic carbon (DOC) release
in diatom-dominated communities. In terms of inorganic nutrient
drawdown and bloom accumulation phase, the dominating
groups behaved as functional surrogates. Dominance
patterns, however, significantly affected C : N : P : Chl a ratios
over the whole bloom event: when diatoms were dominant,
these ratios increased compared to dinoflagellate dominance
or mixed communities. Diatom-dominated communities
sequestered carbon up to 3.6-fold higher than the expectation
based on the Redfield ratio, and 2-fold higher compared
to dinoflagellate dominance. To our knowledge, this is
the first experimental report of consequences of climatically
driven shifts in phytoplankton dominance patterns for carbon
sequestration and related biogeochemical cycles in coastal
seas. Our results also highlight the need for remote sensing
technologies with taxonomical resolution, as the C : Chl a ratio
was strongly dependent on community composition and
bloom stage. Climate-driven changes in phytoplankton dominance
patterns will have far-reaching consequences for major
biogeochemical cycles and need to be considered in climate
change scenarios for marine systems.

An extensive experimental study of ethane oxidation and pyrolysis has been conducted in the high pressure shock tube at UIC covering reflected shock pressures from 5-1000 bar, reaction temperatures up to 1550 K and stoichiometric (Φ = 1 ), fuel rich (Φ = 5), and pyrolytic mixtures. The experimental data has been used to develop a single model that can simulate the whole dataset very well and is the first ethane model capable of simulating experimental results over such an extensive range of pressure, temperature, and stoichiometry. © 2005 Wiley Periodicals, Inc.

https://onlinelibrary.wiley.com/doi/10.1002/kin.20067/full

Key processes such as trophic interactions and nutrient cycling are often influenced by the element content of organ- isms. Previous analyses have led to some preliminary understanding of the relative importance of evolutionary and ecological factors determining animal stoichiometry. However, to date, the patterns and underlying mechanisms of consumer stoichiometry at interspecific and intraspecific levels within natural ecosystems remain poorly investigated. Here, we examine the association between phylogeny, trophic level, body size, and ontogeny and the elemental com- position of 22 arthropod as well as two lizard species from the coastal zone of the Atacama Desert in Chile. We found that, in general, whole-body P content was more variable than body N content both among and within species. Body P content showed a significant phylogenetic signal; however, phylogeny explained only 4% of the variation in body P content across arthropod species. We also found a significant association between trophic level and the element content of arthropods, with carnivores having 15% greater N and 70% greater P contents than herbivores. Elemental scaling relationships across species were only significant for body P content, and even the P content scaling relationship was not significant after controlling for phylogeny. P content did decrease significantly with body size within most arthropod species, which may reflect the size dependence of RNA content in invertebrates. In contrast, larger lizards had higher P contents and lower N:P ratios than smaller lizards, which may be explained by size-associated differences in bone and scale investments. Our results suggests that structural differences in material allocation, trophic level and phylogeny can all contribute to variation in the stoichiometry of desert consumers, and they indicate that the elemental composition of animals can be useful information for identifying broad-scale linkages between nutrient cycling and trophic interactions in terrestrial food webs.

We report the distribution of cobalt (Co) in the Ross Sea polynya during austral summer 2005-2006 and the following austral spring 2006. The vertical distribution of total dissolved Co (dCo) was similar to soluble reactive phosphate (PO 3− 4 ), with dCo and PO 3− 4 showing a significant correlation throughout the water column (r 2 = 0.87, 164 samples). A strong seasonal signal for dCo was observed, with most spring samples having concentrations ranging from ∼45-85 pM, whereas summer dCo values were depleted below these levels by biological activity. Surface transect data from the summer cruise revealed concentrations at the low range of this seasonal variability (∼30 pM dCo), with concentrations as low as 20 pM observed in some regions where PO 3− 4 was depleted to ∼0.

Changes in the ecological stoichiometry of C, N, and P in the pelagic zone are reported from a wholelake manipulation of the food web of Lake 227, an experimentally eutrophied lake at the Experimental Lakes Area, Canada. Addition of northern pike eliminated populations of planktivorous minnows by the third year (1995) after pike introduction, and in the fourth year after pike addition (1996), a massive increase in the abundance of the largebodied cladoceran Daphnia pulicaria occurred. Accompanying this increase in Daphnia abundance, zooplankton community N:P declined, seston concentration and C:P ratio decreased, and dissolved N and P pools increased. During peak abundance, zooplankton biomass comprised a significant proportion of total epilimnetic phosphorus (greater than 30%). During the period of increased Daphnia abundance, concentrations of dissolved inorganic nitrogen (TIN) increased more strongly than dissolved phosphorus (TDP), and thus TIN:TDP ratios were elevated. Sedimentation data indicated that increased grazing led to greatly reduced residence times of C, N, and especially P in the water column during 1996. Finally, previously dominant N-fixing cyanobacteria were absent during 1996. Our results show that strong effects of food-web structure can occur in eutrophic lakes and that stoichiometric mechanisms play a potentially important role in generating these effects.

We present a framework to explain how prey stress responses to predation can resolve context dependency in ecosystem properties and functions such as food chain length, secondary production, elemental stoichiometry, and cycling. We first describe the major nonspecific physiological stress mechanisms and their ecologically relevant consequences. We next synthesize the evidence for prey physiological responses to predation risk and demonstrate that they are similar across taxa and fit well within the general stress paradigm. We then illustrate the utility of our idea by applying our understanding of the ecological consequences of stress to explain how herbivoreprey physiological antipredator responses affect ecosystem dynamics. We hypothesize that stressed herbivores should forage on plant species with higher digestible carbohydrates than should unstressed herbivores to meet heightened energy demands. Increased consumption of carbohydrate-rich plants should reduce their relative abundance in the community, hence altering the quantity and quality of plant litter entering the detrital pool. We further hypothesize that stress should change the elemental composition and energy content of prey excreta, egesta, and carcasses that enter the detrital pool. Finally, prey stress should lower energy and nutrient conversion efficiency and hence the transfer of materials and energy up the food chain, which should, in turn, weaken the association between ecosystem productivity and food chain length.

The symbiosis between cnidarians and dinoflagellate algae of the family Symbiodiniaceae builds the foundation of coral reef
ecosystems. The sea anemone Aiptasia is an emerging model organism promising to advance our functional understanding of this
symbiotic association. Here, we report the observation of a novel phenotype of symbiotic Aiptasia likely induced by severe
nutrient starvation. Under these conditions, developing Aiptasia no longer grow any tentacles. At the same time, fully developed
Aiptasia do not lose their tentacles, yet produce asexual offspring lacking tentacles. This phenotype, termed ‘Wurst’ Aiptasia, can
be easily induced and reverted by nutrient starvation and addition, respectively. Thereby, this observation may offer a new
experimental framework to study mechanisms underlying phenotypic plasticity as well as nutrient cycling within the Cnidaria
– Symbiodiniaceae symbiosis.

We used a subsidy-stress model as a basis for predicting macroinvertebrate community response to a steep gradient of P enrichment in the Florida Everglades, a P-limited wetland ecosystem. We tested the hypothesis that consumers were resource limited and their biomass would show a subsidy response (increase) to low-to-moderate levels of P enrichment, but a stress response (decrease) at high levels of P enrichment because dense emergent macrophytes, particularly Typha, might significantly reduce periphyton food resources. We used a spatially extensive sampling design (14 clusters of 9 sites, 126 total) that incorporated vegetation pattern to evaluate consumer responses along the P gradient. We then conducted a 1-y temporal study at 3 of the 14 clusters to evaluate how seasonal hydrological variation interacted with nutrients to influence consumer biomass. Macroinvertebrate community biomass showed a significant unimodal response to increasing P enrichment consistent with a subsidy-stress relationship. Eight of 12 major taxonomic groups (Amphipoda, Decapoda, Diptera, Empheroptera, Gastropoda, Hirudinea, Odonata, Oligochaeta) had this unimodal response, whereas 3 (Coleoptera, Hemiptera, Isopoda) increased monotonically and 1 (Trichoptera) decreased monotonically in response to P. Periphyton C:N and C:P ratios declined with increasing P, but periphyton cover was minimal at high levels of P enrichment where tall invasive macrophytes limited its growth. The temporal study revealed a subsidy-stress response except after marsh reflooding following the dry season when the most P-enriched clusters of sites had the highest consumer biomass, presumably because drought-induced senescence reduced macrophyte cover, which enabled heavy growth of periphyton. Our results suggest that an interaction between increased quality and decreased quantity of periphyton caused the subsidy-stress patterns observed. We suggest our findings could be generalized to other wetland ecosystems where nutrient enrichment leads to invasion of weedy emergent macrophytes, such as Typha, and elimination of open-canopy habitats rich in periphyton.

Diatoms and dinoflagellates are major bloom-forming phytoplankton groups competing for resources in the oceans and coastal seas. Recent evidence suggests that their competition is significantly affected by climatic factors under ongoing change, modifying especially the conditions for cold-water, spring bloom communities in temperate 5 and arctic regions. We investigated the effects of phytoplankton community composition on spring bloom carbon flows and nutrient stoichiometry in multi-year mesocosm experiments. Comparison of differing communities showed that community structure significantly affected C accumulation parameters, with highest particulate organic carbon (POC) build-up and dissolved organic carbon (DOC) release in diatom-dominated 10 communities. In terms of inorganic nutrient drawdown and bloom accumulation phase, the dominating groups behaved as functional surrogates. Dominance patterns, however, significantly affected C : N : P : Chl a ratios over the whole bloom event: when diatoms were dominant, these ratios increased compared to dinoflagellate dominance or mixed communities. Diatom-dominated communities sequestered carbon up to 3.6-fold 15 higher than the expectation based on the Redfield ratio, and 2-fold higher compared to dinoflagellate dominance. To our knowledge, this is the first experimental report of consequences of climatically driven shifts in phytoplankton dominance patterns for carbon sequestration and related biogeochemical cycles in coastal seas. Our results also highlight the need for remote sensing technologies with taxonomical resolution, as the 20 C : Chl a ratio was strongly dependent on community composition and bloom stage. Climate-driven changes in phytoplankton dominance patterns will have far-reaching consequences for major biogeochemical cycles and need to be considered in climate change scenarios for marine systems.

1. The effects of phosphorus enrichment and grazing snails on a benthic microbial community that builds stromatolic oncolites were examined in an experiment at Rio Mesquites, Cuatro Ciénegas, Mexico. Chemical analyses of stream water samples indicated that overall atomic ratios of total nitrogen (N) to total phosphorus (P) were approximately 110, indicating a strong potential for P-limitation of microbial growth.

2. Phosphorus enrichment involved addition of 5 μmol Na2HPO4 L−1 to streamside microcosms receiving intermittent inputs of stream water while grazer manipulation involved removal of the dominant grazer, the snail Mexithauma quadripaludium. After 7 weeks, we examined responses in organic matter content, C : N : P ratios, metabolism (P removal, primary production, dark respiration, and calcification), and microbial community structure using molecular fingerprinting of 16S rRNA genes.

3. Manipulation of snails did not affect response variables measured in these treatments (organic matter, C : P ratio, P removal rate). However, P enrichment significantly decreased the C : P and N : P ratios of surficial materials in the oncolites (organic matter content was unchanged), increased net and gross photosynthesis (oxygen consumption in the dark was unchanged), increased rates of calcification, and increased diatoms relative to cyanobacteria. Heterotrophic Eubacteria and Archaea were only modestly affected. Thus, our results indicate weak grazing effects but strong impacts of P in this benthic system.

4. We hypothesise that a state of severe P-limitation is imposed on autotrophic production in this food web due, at least in part, to co-precipitation of phosphate during calcite deposition. This produces severe P-limitation of the benthic algae and cyanobacteria, resulting in high C : P ratio of microbial mats relative to the biomass of photoautotrophs (phytoplankton, terrestrial foliage) in other ecosystems. In turn, this high C : P ratio is likely to generate severe stoichiometric constraints on the herbivores, thus limiting their populations and resulting in weak overall grazing impacts.

We examined bait preferences of litter ants along a successional gradient of forests in the Atlantic Forest of Brazil. The ants preferred protein-based baits in secondary forests, yet preferred carbohydrate-based baits in old-growth forests. This suggests a shift in stoichiometric balances between secondary and old-growth forest which might have an impact on the functional interactions in these ecosystems. Therefore, the ecological services offered by secondary habitats may be quite different from those offered by old-growth forests.

behavioural stoichiometry calling effort diet ecological stoichiometry Gryllidae mate attraction phosphorus Adopting a stoichiometric perspective (e.g. the balance of carbon, nitrogen and phosphorus in organisms and their resources) has enhanced our understanding of ecological phenomena at a variety of hierarchical levels of organization. Unfortunately, little is presently known about how stoichiometry directly influences animal behaviour. Here we use a stoichiometric perspective to investigate how phosphorus availability in the environment influences mate attraction behaviour in insects. Using adult male European house crickets (Acheta domesticus), we manipulated the availability of dietary phosphorus and we quantified how survival, propensity to signal acoustically or not ('signallers' versus nonsignalling 'silent' males) and lifetime mate attraction signalling were affected. Dietary phosphorus availability did not influence the proportion of signallers versus silent males. However, signallers fed a diet rich in phosphorus had significantly higher signalling efforts than those that consumed a phosphorus-poor diet. Interestingly, signallers also lived longer than silent males, but neither signaller nor silent male survival was influenced by diet. Our findings suggest that the availability of dietary phosphorus has the potential to impact mating system evolution. Ó

It is a well accepted fact that nutrient limitation of plants affects the growth and survival of herbivores, generally leading to lower performance of herbivores feeding on nutrient stressed plants. The effect of plants' growing conditions on predatory organisms, feeding one trophic level up, has been much less studied, and there is a general consensus that such effects would be small as herbivores often show relatively strong homeostasis with respect to their nutrient content. Here, we challenge this view, and show from several examples that despite the fact that herbivores buffer much of the variance in nutrient stoichiometry of their food, effects of growing conditions of the primary producers can travel up the food chain. We discuss the implications of these findings, and argue that phosphorus limitation of secondary consumers might be more common in marine than in freshwater systems.Ohne Phosphor kein GedankeJacob Moleschott, 1822–1893 (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The response of phytoplankton and bacteria dynamics to turbulence and nutrient availability interactions was studied in natural coastal waters enclosed in 15 l microcosms. The effect of turbulence was examined under 3 different nutrient-induced conditions: nitrogen surplus (N, with initial addition of an excess of nitrogen, N:P ratio = 160), nitrogen:phosphorus ratio balanced (NP, with initial addition of nitrogen and phosphorus as Redfield ratio, N:P ratio = 16) and control (C, no nutrient addition). Turbulence (ε = 0.055 cm 2 s -3 ) was generated by vertically oscillating grids. The experiment lasted for 8 d and samples were generally taken daily for nutrient and plankton measurements. Turbulence increased the relative importance of phytoplankton to bacteria when nutrients were added, while in the control the effect of turbulence was negligible. Turbulence also influenced the species' composition and the size distribution of the phytoplankton community. The relative contribution of diatoms to total phytoplankton biomass and the average cell size were higher under turbulence, particularly in N and NP treatments. The results of these experiments indicate the importance of considering the hydrodynamic conditions in studies addressing competition for nutrients among different osmotrophic organisms in plankton communities.

Litter decomposition is driven by saprotrophic microbial communities. The structure of this community varies over the course of decomposition, which has been linked to the chemistry of litter resources. Here, we test the hypothesis that leaf litter from different tree species becomes more similar in terms of litter stoichiometry, C-biochemistry during the course of decomposition (convergence). We also test if these variations can be linked to shifts in microbial community structure and abundance. For this reason, leaf litter of four deciduous tree species — beech (Fagus sylvatica), oak (Quercus robur), alder (Alnus glutinosa) and ash (Fraxinus excelsior) were sampled from a temperate forest in February, May and September 2010. We measured variations in leaf litter stoichiometry by elemental concentrations, C-biochemistry with Fourier transform infrared (FTIR) spectroscopy and litter microbial community structure and abundance with phospholipid fatty acid (PLFA) analysis. For litter from beech, oak and ash, C:N and C:P ratio converged with time when exposed to the same environmental conditions during degradation. In contrast, C:nutrient ratios increased in alder litter over time. Litter C-biochemistry was to a large extent related to shifts in C:N ratios. Principal component analysis PCA of FTIR bands, revealed that divergence in C-biochemistry over the course of decomposition was dependent on litter type, and hence, with initial C:N ratio. Litter-decomposing bacterial community was highly relevant to C-biochemistry and environmental conditions (temperature and moisture) while fungi community was more nutrients-related. In conclusion, initially wide C:nutrient ratios tend to converge during decay; while nutrient limitation may lead to divergence of stoichiometry. In general, there was a trend towards divergence of C-biochemistry and microbial community structure.

We measured changes in carbon (C), nitrogen (N) and phosphorus (P) concentrations and mass of 10 foliar litters decomposing over 12 years at 21 sites across Canada, ranging from subarctic to temperate, to evaluate the influence of litter quality (nature) and forest floor (nurture) on N and P dynamics. Most litters lost P faster than N, relative to C, except in one litter which had a high initial C:P quotient (2,122). Net N loss occurred at mass C:N quotients of between 33 and 68, positively correlated with the C:N quotient in the original litter, and net P loss likely occurred at C:P quotients between 800 and 1,200. Forest floor properties also influenced N and P dynamics: the higher the C: N or C:P quotient in the surface soil organic matter, the smaller the proportion of initial N or P left in the decomposing litter, relative to C. There was a convergence of C:N and C:P quotients as the litters decomposed, with an overall mass ratio of 427:17:1 when the litters reached 20% original C remaining. These results, covering a wide range of sites and litters and thus decomposition rates, showed that the C:N:P quotients followed similar trajectories and converged as the litters decomposed. The relative loss of N and P was affected by both the initial litter nutrient concentration and the chemistry of the site forest floor, with the former being more important than the latter, resulting in spatial variations in nutrient content of the forest floor.

Light (20-450 μmol photons m-2 s-1), temperature (3-11°C) and inorganic nutrient composition
(nutrient replete and N, P and Si limitation) were manipulated to study their combined influence
on growth, stoichiometry (C:N:P:Chl a) and primary production of the cold water
diatom Chaetoceros wighamii. During exponential growth, the maximum growth rate (~0.8
d-1) was observed at high temperture and light; at 3°C the growth rate was ~30% lower
under similar light conditions. The interaction effect of light and temperature were clearly visible
from growth and cellular stoichiometry. The average C:N:P molar ratio was 80:13:1 during
exponential growth, but the range, due to different light acclimation, was widest at the
lowest temperature, reaching very low C:P (~50) and N:P ratios (~8) at low light and temperature.
The C:Chl a ratio had also a wider range at the lowest temperature during exponential
growth, ranging 16-48 (weight ratio) at 3°C compared with 17-33 at 11°C. During exponential
growth, there was no clear trend in the Chl a normalized, initial slope (α*) of the photosynthesis-
irradiance (PE) curve, but the maximum photosynthetic production (Pm) was highest for
cultures acclimated to the highest light and temperature. During the stationary growth
phase, the stoichiometric relationship depended on the limiting nutrient, but with generally increasing
C:N:P ratio. The average photosynthetic quotient (PQ) during exponential growth
was 1.26 but decreased to <1 under nutrient and light limitation, probably due to photorespiration.
The results clearly demonstrate that there are interaction effects between light, temperature
and nutrient limitation, and the data suggests greater variability of key parameters
at low temperature. Understanding these dynamics will be important for improving models of
aquatic primary production and biogeochemical cycles in a warming climate.

1. Among vertebrates, herbivores have longer digestive tracts than animals at higher trophic levels, a pattern thought to reflect a trade-off between digestive efficiency and tissue maintenance costs. However, phylogenetic influences on this pattern have rarely been considered. Taxa that have undergone diversification accompanied by dietary shifts provide a powerful opportunity to examine the relationship between diet and intestine length while accounting for phylogeny. 2. In this paper we assess the relationship between diet and intestine length in the cichlid fishes of Lake Tanganyika, which are renowned for their diversity of species and trophic strategies. 3. First, we test the effect of trophic position on intestine length across 32 species, while controlling for phylogeny. Trophic position was inferred from nitrogen stable isotopes, which provide a temporally integrated, quantitative perspective on the complex diets of tropical fish. Second, we examine patterns of intraspecific variation in intestine length of an algivorous cichlid (Tropheus brichardi) along a natural spatial gradient in algal nitrogen content. 4. Trophic position explains 51% of size-standardized variation in intestine length after accounting for phylogeny. Accounting for phylogeny does not substantially alter the relationship between trophic position and intestine length, despite the existence of phylogenetic signal in both traits. Thus, diet is a strong predictor of variation at the interspecific level. 5. There is a striking inverse relationship between intestine length and algal nutrient content among populations of T. brichardi, suggesting substantial plasticity in response to food quality, and thus a strong dietary influence on patterns of intraspecific variation. 6. Diet is a strong predictor of intestine length at both intra-and interspecific scales, indicating that fish adjust their phenotype to balance nutritional needs against energetic costs. Furthermore, functional explanations for trophic diversification of cichlid fishes in the African Great Lakes have long focused on jaw structures, but our results indicate that intestinal plasticity in response to diet quality may also be an important mechanism for accommodating trophic shifts during evolutionary radiations.

Difficulties to simply transfer trophic cascade theory from temperate to tropical lakes are now well recognized. Many mechanisms trying to explain top-down divergences between these systems have been proposed, such as lack of key species of herbivorous zooplankton, absence of seasonality in fish reproduction, cyanobacteria development, or differences in fish foraging behaviour. Very few studies have considered bottom-up mechanisms, in particular differences in nutrient recycling and nutrient limitation between the two types of ecosystems. According to the ecological stoichiometry theory, fish-induced alterations of food-web structure could modify the efficiency of consumer-driven nutrient recycling by changing the relative biomass contribution of species in food webs. Consequently, by mostly considering top-down processes, one could underestimate consequences on nutrient availability for phytoplankton growth. In this paper, we compared the results of two mesocosm experiments carried out in temperate and tropical areas, each manipulating foodweb structure via the presence or absence of fish. We found trophic cascades in both experiments, but differences between fishless and fish treatments were greater in temperate than in tropical systems. In the tropical experiment, the observed effects could not be supported by classical zooplankton community alteration or by cyanobacteria prevalence. Our results suggest a key contribution of fish nitrogen-excretion to phytoplankton growth in mostly nitrogen-limited tropical systems. Differences in stoichiometric response to food-web structure alteration between temperate and tropical lakes could thus represent a major difference between the two systems. Our study stresses the need for further studies that would allow robust generalization on the functioning of freshwater temperate and tropical ecosystems.

1. The transition from carbon (C) to phosphorus (P) limited growth in Daphnia depends not only on the C : P ratio in seston, i.e. food quality, but also on food quantity. Carbon is commonly believed to be limiting at low food because of the energetic demands of basal metabolism. The critical C : P ratio in seston (otherwise known as the threshold elemental ratio, TER) above which P is limiting would then be high when food is scarce. 2. A new model that differentiates between the C : P requirements for growth and maintenance is presented that includes terms for both C and P in basal metabolism. At low food the calculated TERs for Daphnia of around 230 are only slightly higher than values of 200 or so at high intake. Seston C : P often exceeds 230, particularly in oligotrophic lakes where phytoplankton concentration is low and detritus dominates the diet, indicating the potential for limitation by P. 3. The analysis highlights the importance of P, as well as C, in maintenance metabolism and the overall metabolic budget, such that food quality is of importance even when intake is low. Further measurements of C and P metabolism at low food, in particular basal respiration and excretion rates, are needed in order to improve our understanding of the interacting roles of food quantity and quality in zooplankton nutrition.

Understanding the factors that control the growth of heterotrophic organisms is central to predicting food web interactions and biogeochemical cycling within ecosystems. We present a new framework, Geometric Stoichiometry (GS), that unifies the disciplines of Nutritional Geometry (NG) and Ecological Stoichiometry (ES) by extending the equations of ES to incorporate core NG concepts, including macromolecules as currencies and the ability of animals to select foods that balance deficits and excesses of nutrients. The resulting model is used to investigate regulation of consumer growth by dietary protein:carbohydrate ratio. Growth on protein-poor diets is limited by nitrogen. Likewise, we show that growth is also diminished on protein-rich diets and that this can be mechanistically explained by means of a metabolic penalty that arises when animals use protein for energy generation. These penalties, which are incurred when dealing with the costs of producing and excreting toxic nitrogenous waste, have not hitherto been represented in standard ES theory. In order to incorporate GS within ecosystem and biogeochemical models, a new generation of integrated theoretical and experimental studies based on unified concepts of NG and ES is needed, including measurements of food selection, biomass, growth and associated physiology, and involving metabolic penalties.

Responses of detrital pathways to nutrients may differ fundamentally from pathways involving living plants: basal carbon resources can potentially decrease rather than increase with nutrient enrichment. Despite the potential for nutrients to accelerate heterotrophic processes and fluxes of detritus, few studies have examined detritus-nutrient dynamics at whole-ecosystem scales. We quantified organic matter (OM) budgets over three consecutive years in two detritus-based Appalachian (USA) streams. After the first year, we began enriching one stream with low-level nitrogen and phosphorus inputs. Subsequent effects of nutrients on outputs of different OM compartments were determined using randomized intervention analysis. Nutrient addition did not affect dissolved or coarse particulate OM export but had dramatic effects on fine particulate OM (FPOM) export at all discharges relative to the reference stream. After two years of enrichment, FPOM export was 340% higher in the treatment stream but had decreased by 36% in the reference stream relative to pretreatment export. Ecosystem respiration, the dominant carbon output in these systems, also increased in the treatment stream relative to the reference, but these changes were smaller in magnitude than those in FPOM export. Nutrient enrichment accelerated rates of OM processing, transformation, and export, potentially altering food-web dynamics and ecosystem stability in the long term. The results of our large-scale manipulation of a detrital ecosystem parallel those from analogous studies of soils, in which net loss of organic carbon has often been shown to result from experimental nutrient addition at the plot scale. Streams are useful model systems in which to test the effects of nutrients on ecosystem-scale detrital dynamics because they allow both the tracking of OM conversion along longitudinal continua and the integrated measurement of fluxes of transformed material through downstream sites.

Plant-herbivore interactions mediate the trophic structure of ecosystems. We use a comprehensive data set extracted from the literature to test the relative explanatory power of two contrasting bodies of ecological theory, the metabolic theory of ecology (MTE) and ecological stoichiometry (ES), for per-capita and population-level rates of herbivory across ecosystems. We found that ambient temperature and herbivore body size (MTE) as well as stoichiometric mismatch (ES) both constrained herbivory, but at different scales of biological organization. Herbivore body size, which varied over 11 orders of magnitude, was the primary factor explaining variation in per-capita rates of herbivory. Stoichiometric mismatch explained more variation in population-level herbivory rates and also in per-capita rates when we examined data from within functionally similar trophic groups (e.g. zooplankton). Thus, predictions from metabolic and stoichiometric theories offer complementary explanations for patterns of herbivory that operate at different scales of biological organization.

Extracellular enzymes are the proximate agents of organic matter decomposition and measures of these activities can be used as indicators of microbial nutrient demand. We conducted a global-scale meta-analysis of the seven-most widely measured soil enzyme activities, using data from 40 ecosystems. The activities of b-1,4-glucosidase, cellobiohydrolase, b-1,4-N-acetylglucosaminidase and phosphatase g )1 soil increased with organic matter concentration; leucine aminopeptidase, phenol oxidase and peroxidase activities showed no relationship. All activities were significantly related to soil pH. Specific activities, i.e. activity g )1 soil organic matter, also varied in relation to soil pH for all enzymes. Relationships with mean annual temperature (MAT) and precipitation (MAP) were generally weak. For hydrolases, ratios of specific C, N and P acquisition activities converged on 1 : 1 : 1 but across ecosystems, the ratio of C : P acquisition was inversely related to MAP and MAT while the ratio of C : N acquisition increased with MAP. Oxidative activities were more variable than hydrolytic activities and increased with soil pH. Our analyses indicate that the enzymatic potential for hydrolyzing the labile components of soil organic matter is tied to substrate availability, soil pH and the stoichiometry of microbial nutrient demand. The enzymatic potential for oxidizing the recalcitrant fractions of soil organic material, which is a proximate control on soil organic matter accumulation, is most strongly related to soil pH. These trends provide insight into the biogeochemical processes that create global patterns in ecological stoichiometry and organic matter storage.

To provide a reference for wetlands elsewhere we analysed soil nutrients and the vegetation of floodplains and fens in the relatively undisturbed Biebrza-valley, Poland. Additionally, by studying sites along a water-table gradient, and by comparing pairs of mown and unmown sites, we aimed with exploring long-term effects of drainage and annual hay-removal on nutrient availabilities and vegetation response. In undrained fens and floodplains, N mineralization went slowly (0-30 kg N ha -1 year -1 ) but it increased strongly with decreasing water table (up to 120 kg N ha -1 year -1 ). Soil N, P and K pools were small in the undisturbed mires. Drainage had caused a shift from fen to meadow species and the disappearance of bryophytes. Biomass of vascular plants increased with increasing N mineralization and soil P. Annual hayremoval tended to have reduced N mineralization and soil K pools, but it had increased soil P. Moreover, N concentrations in vascular plants were not affected, but P and K concentrations and therefore N:P and N:K ratios tended to be changed. Annual hay-removal had induced a shift from P to K limitation in the severely drained fen, and from P to N limitation in the floodplain. The low nutrient availabilities and productivity of the undisturbed Biebrza mires illustrate the vulnerability of such mires to eutrophication in Poland and elsewhere. In nutrient-enriched areas, hay removal may prevent productivity increase of the vegetation, but also may severely alter N:P:K stoichiometry, induce K-limitation at drained sites, and alter vegetation structure and composition.

In ecosystems, species interact with other species directly and through abiotic factors in multiple ways, often forming complex networks of various types of ecological interaction. Out of this suite of interactions, predator-prey interactions have received most attention. The resulting food webs, however, will always operate simultaneously with networks based on other types of ecological interaction, such as through the activities of ecosystem engineers or mutualistic interactions. Little is known about how to classify, organize and quantify these other ecological networks and their mutual interplay. The aim of this paper is to provide new and testable ideas on how to understand and model ecosystems in which many different types of ecological interaction operate simultaneously. We approach this problem by first identifying six main types of interaction that operate within ecosystems, of which food web interactions are one. Then, we propose that food webs are structured among two main axes of organization: a vertical (classic) axis representing trophic position and a new horizontal 'ecological stoichiometry' axis representing decreasing palatability of plant parts and detritus for herbivores and detrivores and slower turnover times. The usefulness of these new ideas is then explored with three very different ecosystems as test cases: temperate intertidal mudflats; temperate short grass prairie; and tropical savannah.

We conducted a meta-analysis of the available literature to assess the effect of decapod
crustacean macroconsumers on the processing and invertebrate colonization of leaf detritus
in streams. Supplementary methodological (experimental set-up), geographical (i.e. latitude,
climate) and biological (i.e. macroconsumers body size, detritus quality expressed as initial C:
N ratio) data were collected, with the aim of assessing their influence on effect sizes variability.
Overall, our results indicated some important effects of decapod crustacean macroconsumers
on both detritus processing and colonization by invertebrates. Among the different
factors examined, detritus quality and macroconsumer body size were important for
predicting detritus processing and invertebrate colonization effects, respectively. This
indicates that the pivotal role played by decapod crustacean macroconsumers on leaf
decomposition, food webs, and wider stream ecosystem functioning, may be regulated by the
interplay of both detritus chemistry and consumer’s body size. The limitations and
inadequacies of the analyzed literature are discussed.

Belowground organisms often display a shift in their mass-abundance scaling relationships due to environmental factors such as soil chemistry and atmospheric deposition. Here we present new empirical data that show strong differences in allometric scaling according to whether the resolution at the local scale is based on a taxonomic or a functional classification, while only slight differences arise according to soil environmental conditions. For the first time, isometry (an inverse 1:1 proportion) is recognized in mass-abundance relationships, providing a functional signal for constant biomass distribution in soil biota regardless of discrete trophic levels. Our findings are in contrast to those from aquatic ecosystems, in that higher trophic levels in soil biota are not a direct function of increasing body mass.