Countervailing effects of atrazine on water recreation: How do recreators evaluate them?

This is the publisher's version, also available electronically from http://onlinelibrary.wiley.com/doi/10.1029/2002WR001598/abstract;jsessionid=E412CD5D75BE2BF9BC7052CBAAC6509E.f02t04.This paper examines the countervailing effects of atrazine on water recreational choices. The presence of atrazine in waterbodies potentially reduces the symptoms of eutrophication, which is a condition of low water quality due to nutrient enrichment. Eutrophication frequently undermines recreational enjoyment and diminishes recreational use of affected waterbodies. Thus increased atrazine concentrations could induce greater recreation. However, atrazine also potentially decreases the mass and size of fish populations; this loss potentially reduces recreational use. To examine empirically these countervailing effects on recreational use, this study gathers and generates data on actual recreation under initial water quality conditions and stated recreation under hypothetical quality conditions, which vary eutrophication-related and fish-related quality independently and jointly. This economic study uses a travel cost framework and the associated contingent behavior framework to analyze these data

Responses of a bacterial pathogen to phosphorus limitation of its aquatic invertebrate host

Host nutrition is thought to affect the establishment, persistence, and severity of pathogenic infections. Nutrient-deficient foods possibly benefit pathogens by constraining host immune function or benefit hosts by limiting parasite growth and reproduction. However, the effects of poor elemental food quality on a host’s susceptibility to infection and disease have received little study. Here we show that the bacterial microparasite Pasteuria ramosa is affected by the elemental nutrition of its aquatic invertebrate host, Daphnia magna. We found that high food carbon : phosphorus (C:P) ratios significantly reduced infection rates of Pasteuria in Daphnia and led to lower within-host pathogen multiplication. In addition, greater virulent effects of bacterial infection on host reproduction were found in Daphniaconsuming P-deficient food. Poor Daphnia elemental nutrition thus reduced the growth and reproduction of its bacterial parasite, Pasteuria. The effects of poor host nutrition on the pathogen were further evidenced by Pasteuria’s greater inhibition of reproduction in P-limited Daphnia. Our results provide strong evidence that elemental food quality can significantly influence the incidence and intensity of infectious disease in invertebrate hosts.We thank H. Foy, C. Hibbert, M. Kingsbury, S. McCarthy, and D. Woolnough for their assistance with the experiments. This work was supported by grants from the Natural Sciences and Engineering Research Council of Canada and Trent University

Resources, mortality, and disease ecology: Importance of positive feedbacks between host growth rate and pathogen dynamics

This is an Accepted Manuscript of an article published by Taylor & Francis in Israel Journal of Ecology and Evolution in 2015, available online: http://www.tandfonline.com/10.1080/15659801.2015.1035508.Resource theory and metabolic scaling theory suggest that the dynamics of a pathogen within a host should strongly depend upon the rate of host cell metabolism. Once an infection occurs, key ecological interactions occur on or within the host organism that determine whether the pathogen dies out, persists as a chronic infection, or grows to densities that lead to host death. We hypothesize that, in general, conditions favoring rapid host growth rates should amplify the replication and proliferation of both fungal and viral pathogens. If a host population experiences an increase in mortality, to persist it must have a higher growth rate, per host, often reflecting greater resource availability per capita. We hypothesize that this could indirectly foster the pathogen, which also benefits from increased within-host resource turnover. We first bring together in a short review a number of key prior studies which illustrate resource effects on viral and fungal pathogen dynamics. We then report new results from a semi-continuous cell culture experiment with SHIV, demonstrating that higher mortality rates indeed can promote viral proliferation. We develop a simple model that illustrates dynamical consequences of these resource effects, including interesting effects such as alternative stable states and oscillatory dynamics. Our paper contributes to a growing body of literature at the interface of ecology and infectious disease epidemiology, emphasizing that host abundances alone do not drive community dynamics: the physiological state and resource content of infected hosts also strongly influence host-pathogen interactions

Constraints on primary producer n:p stoichiometry along n:p supply ratio gradients

A current principle of ecological stoichiometry states that the nitrogen to phosphorus ratio (N:P) of primary producers should closely match that from environmental nutrient supplies. This hypothesis was tested using data from ponds in Michigan, USA, a freshwater mesocosm experiment, a synthesis of studies from diverse systems (cultures, lakes, streams, and marine and terrestrial environments), and simple dynamic models of producer growth and nutrient content. Unlike prior laboratory studies, the N:P stoichiometry of phytoplankton in Michigan ponds clustered around and below the Redfield ratio (7.2:1 by mass), despite wide variation in N:P supply ratios (2:1–63:1 by mass) and the presence of grazers. In a mesocosm experiment, the N:P stoichiometry of phytoplankton cells again deviated from a nearly 1:1 relationship with N:P supply. Phytoplankton seston exhibited lower N:P content than expected at high N:P supply ratios, and often higher N:P content than anticipated at low N:P supply ratios, regardless of herbivore presence. Similar deviations consistently occur in the N:P stoichiometry of algae and plants in the other diverse systems. The models predicted that both high loss rates (sinking, grazing) and physiological limits to nutrient storage capacity could attenuate producer stoichiometry. In the future, research should evaluate how limits to elemental plasticity of producers can influence the role of stoichiometry in structuring communities and ecosystem processes.We thank T. Darcy-Hall, A. Downing, P. Geddes, and N. Howe for help with tank and field sampling; and C. Klausmeier, G. Mittelbach, two anonymous reviewers, and Editor P. Leavitt for very helpful comments on the manuscript. We analyzed the C:N samples in the Robertson lab at Kellogg Biological Station (KBS) with the help of A. Corbin and T. Darcy-Hall. Thanks also go to G. Mittelbach, N. Consolatti, A. Tessier, and P. Woodruff at KBS for technical support. M. Bishop of the Michigan DNR permitted us to sample ponds in Barry and Middleville State Game Areas. Primary funding came from NSF DEB 98-15799 to Mathew A. Leibold and Val H. Smith. Spencer R. Hall was also supported by an NSF Graduate Fellowship, a University of Chicago Harper Fellowship and Hinds Fund Award, a Department of Education GAANN training grant, and a NSF DDIG (DEB 01-05014, P.I., Mathew Leibold). Some of the data described in this article were produced by the U.S. Environmental Protection Agency through its Environmental Monitoring and Assessment Program (EMAP). This is KBS contribution #1169

Stoichiometry and planktonic grazer composition over gradients of light, nutrients, and predation risk

Mechanisms that explain shifts in species composition over environmental gradients continue to intrigue ecologists. Ecological stoichiometry has recently provided a new potential mechanism linking resource (light and nutrient) supply gradients to grazer performance via elemental food-quality mechanisms. More specifically, it predicts that light and nutrient gradients should determine the relative dominance of P-rich taxa, such as Daphnia, in grazer assemblages. We tested this hypothesis in pond mesocosms (cattle tanks) by creating gradients of resource supply and predation risk, to which we added diverse assemblages of algal producer and zooplankton grazer species. We then characterized the end-point composition of grazer assemblages and quantity and elemental food quality of edible algae. We found that somatically P-rich Daphnia only dominated grazer assemblages in high-nutrient, no-predator treatments. In these ecosystems, P sequestered in producers exceeded a critical concentration. However, other grazers having even higher body P content did not respond similarly. These grazers were often abundant in low-nutrient environments with poorer food quality. At face value, this result is problematic for ecological stoichiometry because body composition did not correctly predict response of these other species. However, two potential explanations could maintain consistency with stoichiometric principles: species could differentially use a high-P resource (bacteria), or body composition might not always directly correlate with nutrient demands of grazers. Although our data cannot differentiate between these explanations, both suggest potential avenues for future empirical and theoretical study.We thank T. Darcy, A. Downing, P. Geddes, and N. Howe for help with sampling, and G. Dwyer, T. Wootton, J. Bergelson, D. Spiller, W. DeMott, and an anonymous reviewer for their comments on the manuscript. We analyzed the C:N 2300 SPENCER R. HALL ET AL. Ecology, Vol. 85, No. 8 samples in the Robertson laboratory at Kellogg Biological Station (KBS) with the help of A. Corbin and T. Darcy. Thanks also go to G. Mittelbach, N. Consolatti, A. Tessier, and P. Woodruff at KBS for technical support. M. Bishop of the Michigan DNR permitted us to sample ponds in Barry and Middleville SGAs. Primary funding came from NSF DEB 98-15799 to M. A. Leibold and V. H. Smith. S. R. Hall was also supported by an NSF Graduate Fellowship, a University of Chicago Harper Fellowship and Hinds Fund Award, a Department of Education GAANN training grant, and a NSF DDIG (DEB 01-05014, PI Mathew Leibold). This is KBS contribution number 1128

Grazers, producer stoichiometry, and the light : nutrient hypothesis revisited.

The stoichiometric light : nutrient hypothesis (LNH) links the relative supplies of key resources with the nutrient content of tissues of producers. This resource-driven variation in producer stoichiometry, in turn, can mediate the efficiency of grazing. Typically, discussions of the LNH attribute this resource–stoichiometry link to bottom-up effects of light and phosphorus, which are mediated through producer physiology. Emphasis on bottom-up effects implies that grazers must consume food of quality solely determined by resource supply to ecosystems (i.e., they eat what they are served). Here, we expand upon this largely bottom up interpretation with evidence from pond surveys, a mesocosm experiment, and a model. Data from shallow ponds showed the ‘‘LNH pattern’’ (positive correlation of an index of light: phosphorus supply with algal carbon : phosphorus content). However, algal carbon: phosphorus content also declined as zooplankton biomass increased in the ponds. The experiment and model confirmed that this latter correlation was partially caused by the various bottom-up and top-down roles of grazers: the LNH pattern emerged only in treatments with crustacean grazers, not those without them. Furthermore, model and experiment clarified that another bottom-up factor, natural covariation of nitrogen : phosphorus ratios with light : phosphorus supply (as seen in ponds), does not likely contribute to the LNH pattern. Finally, the experiment produced correlations between shifts in species composition of algae, partially driven by grazing effects of crustaceans, and algal stoichiometry. These shifts in species composition might shape stoichiometric response of producer assemblages to resource supply and grazing, but their consequences remain largely unexplored. Thus, this study accentuated the importance of grazing for the LNH; deemphasized a potentially confounding, bottom-up factor (covarying nitrogen : phosphorus supply); and highlighted an avenue for future research for the LNH (grazer-mediated shifts in producer composition).We thank T. Darcy-Hall, A. Downing, P. Geddes, and N. Howe for help with sampling the cattle tank experiment and natural ponds. We analyzed the C:N samples in the Robertson lab at the W. K. Kellogg Biological Station (KBS) with the help of A. Corbin and T. Darcy-Hall. Thanks also go to G. Mittelbach, N. Consolatti, A. Tessier, and P. Woodruff for technical support. Finally, S. Diehl kindly provided us with data from his experiments. Primary funding came from NSF DEB 98-15799, DEB 02-35579, and funds from Indiana University. This is KBS contribution number 1277

Inedible Producers in Food Webs: Controls on Stoichiometric Food Quality and Composition of Grazers

Ecological stoichiometry and food web theories focus on distinct mechanisms that shape communities. These mechanisms, however, likely interact in ways that neither theory alone addresses. To illustrate, we show how a model that tracks flow of energy and nutrients through two producers and two grazers reveals two indirect, interrelated roles for “neutrally inedible” producers. First, inedible producers can exert controls over the nutrient content of edible producers and indirectly influence whether grazers are nutrient or energy limited. Second, through these controls, inedible producers can shape community assembly by excluding grazers that are weak competitors for nutrients contained in edible producers. A mesocosm experiment revealed patterns consistent with both predictions: high abundances of inedible algae were accompanied by low phosphorus contents of edible algae and low abundances of the grazer Daphnia. Both lines of inference suggest that interactions between stoichiometry and plant heterogeneity may shape plankton communities

Nitrogen, Phosphorus, and Eutrophication in Streams

Flowing waters receive substantial nutrient inputs, including both nitrogen (N) and phosphorus (P), in many parts of the world. Eutrophication science for rivers and streams has unfortunately lagged behind that for lakes, and results from lakes might inform those interested in stream eutrophication. A key controversy in lake eutrophication science is the relative importance of controlling P and N in water quality management, and we are interested how the science of this controversy transfers to flowing waters. A literature review indicates (1) stream benthic chlorophyll is significantly correlated to both total N and total P in the water column, with both nutrients explaining more variance than either considered alone; (2) nutrients have increased substantially in many rivers and streams of the United States over reference conditions, and strong shifts in N and P stoichiometry have occurred as well; (3) bioassays often indicate N responses alone or in concert with P responses for autotrophic (primary production and chlorophyll) and heterotrophic (respiration) responses; (4) both heterotrophic and autotrophic processes are influenced by the availability of N and P; and (5) N-fixing cyanobacteria usually do not seem to be able to fully satisfy N limitations in rivers and streams when P is present in excess of N. These data suggest both N and P control should be considered in the eutrophication management of streams

Microbiology and ecology are vitally important to premedical curricula

Despite the impact of the human microbiome on health, an appreciation of microbial ecology is yet to be translated into mainstream medical training and practice. The human microbiota plays a role in the development of the immune system, in the development and function of the brain, in digestion, and in host defense, and we anticipate that many more functions are yet to be discovered. We argue here that without formal exposure to microbiology and ecology—fields that explore the networks, interactions and dynamics between members of populations of microbes—vitally important links between the human microbiome and health will be overlooked. This educational shortfall has significant downstream effects on patient care and biomedical research, and we provide examples from current research highlighting the influence of the microbiome on human health. We conclude that formally incorporating microbiology and ecology into the premedical curricula is invaluable to the training of future health professionals and critical to the development of novel therapeutics and treatment practices

Extrinsic and intrinsic controls of zooplankton diversity in lakes

Pelagic crustacean zooplankton were collected from 336 Norwegian lakes covering a wide range of latitude, altitude, lake area, mean depth, production (as chlorophyll a), and fish community structure. Mean zooplankton species richness during the ice-free season was generally low at high latitudes and altitudes. Further, lower species richness was recorded in western lakes, possibly reflecting constraints on migration and dispersal. However, despite obvious spatial limitations, geographic boundaries were only weak predictors of mean zooplankton richness. Similarly, lake surface area did not contribute positively to mean richness such as seen in other ecosystem surveys. Rather, intrinsic factors such as primary production and fish community (planktivore) structure were identified by regression analysis as the major predictors of zooplankton diversity, while a positive correlation was observed between species richness and total zooplankton biomass. However, in spite of a large number of variables included in this study, the predictive power of multiple regression models was modest (<50% variance explained), pointing to a major role for within-lake properties, as yet unidentified intrinsic forces, stochasticity, or dispersal as constraints on zooplankton diversity in these lakes