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1.
Nature ; 578(7795): 425-431, 2020 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-32051592

RESUMO

Bacteriophages typically have small genomes1 and depend on their bacterial hosts for replication2. Here we sequenced DNA from diverse ecosystems and found hundreds of phage genomes with lengths of more than 200 kilobases (kb), including a genome of 735 kb, which is-to our knowledge-the largest phage genome to be described to date. Thirty-five genomes were manually curated to completion (circular and no gaps). Expanded genetic repertoires include diverse and previously undescribed CRISPR-Cas systems, transfer RNAs (tRNAs), tRNA synthetases, tRNA-modification enzymes, translation-initiation and elongation factors, and ribosomal proteins. The CRISPR-Cas systems of phages have the capacity to silence host transcription factors and translational genes, potentially as part of a larger interaction network that intercepts translation to redirect biosynthesis to phage-encoded functions. In addition, some phages may repurpose bacterial CRISPR-Cas systems to eliminate competing phages. We phylogenetically define the major clades of huge phages from human and other animal microbiomes, as well as from oceans, lakes, sediments, soils and the built environment. We conclude that the large gene inventories of huge phages reflect a conserved biological strategy, and that the phages are distributed across a broad bacterial host range and across Earth's ecosystems.

2.
Trends Ecol Evol ; 34(4): 355-368, 2019 04.
Artigo em Inglês | MEDLINE | ID: mdl-30745252

RESUMO

Animals experience varying levels of predation risk as they navigate heterogeneous landscapes, and behavioral responses to perceived risk can structure ecosystems. The concept of the landscape of fear has recently become central to describing this spatial variation in risk, perception, and response. We present a framework linking the landscape of fear, defined as spatial variation in prey perception of risk, to the underlying physical landscape and predation risk, and to resulting patterns of prey distribution and antipredator behavior. By disambiguating the mechanisms through which prey perceive risk and incorporate fear into decision making, we can better quantify the nonlinear relationship between risk and response and evaluate the relative importance of the landscape of fear across taxa and ecosystems.


Assuntos
Ecossistema , Comportamento Predatório , Animais , Medo
3.
ISME J ; 13(6): 1618-1634, 2019 06.
Artigo em Inglês | MEDLINE | ID: mdl-30809011

RESUMO

Blooms of planktonic cyanobacteria have long been of concern in lakes, but more recently, harmful impacts of riverine benthic cyanobacterial mats been recognized. As yet, we know little about how various benthic cyanobacteria are distributed in river networks, or how environmental conditions or other associated microbes in their consortia affect their biosynthetic capacities. We performed metagenomic sequencing for 22 Oscillatoriales-dominated (Cyanobacteria) microbial mats collected across the Eel River network in Northern California and investigated factors associated with anatoxin-a producing cyanobacteria. All microbial communities were dominated by one or two cyanobacterial species, so the key mat metabolisms involve oxygenic photosynthesis and carbon oxidation. Only a few metabolisms fueled the growth of the mat communities, with little evidence for anaerobic metabolic pathways. We genomically defined four cyanobacterial species, all which shared <96% average nucleotide identity with reference Oscillatoriales genomes and are potentially novel species in the genus Microcoleus. One of the Microcoleus species contained the anatoxin-a biosynthesis genes, and we describe the first anatoxin-a gene cluster from the Microcoleus clade within Oscillatoriales. Occurrence of these four Microcoleus species in the watershed was correlated with total dissolved nitrogen and phosphorus concentrations, and the species that contains the anatoxin-a gene cluster was found in sites with higher nitrogen concentrations. Microbial assemblages in mat samples with the anatoxin-a gene cluster consistently had a lower abundance of Burkholderiales (Betaproteobacteria) species than did mats without the anatoxin-producing genes. The associations of water nutrient concentrations and certain co-occurring microbes with anatoxin-a producing Microcoleus motivate further exploration for their roles as potential controls on the distributions of toxigenic benthic cyanobacteria in river networks.


Assuntos
Cianobactérias/isolamento & purificação , Cianobactérias/metabolismo , Rios/microbiologia , Tropanos/metabolismo , California , Cianobactérias/classificação , Cianobactérias/genética , Lagos/microbiologia , Metagenômica , Nitrogênio/metabolismo , Fósforo/metabolismo , Filogenia , Rios/química
4.
Oecologia ; 188(3): 821-835, 2018 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-30099603

RESUMO

The ecological importance of the common hippopotamus (Hippopotamus amphibius) in aquatic ecosystems is becoming increasingly well known. These unique megaherbivores are also likely to have a formative influence on the terrestrial ecosystems in which they forage. In this study, we employed a novel exclosure design to exclude H. amphibius from experimental plots on near-river grasslands. Our three-year implementation of this experiment revealed a substantial influence of H. amphibius removal on both plant communities and soil chemistry. H. amphibius significantly reduced grassland canopy height, increased the leafiness of common grasses, reduced woody plant abundance and size, and increased the concentrations of several soil elements. Many of the soil chemistry changes that we experimentally induced by exclusion of H. amphibius were mirrored in the soil chemistry differences between naturally occurring habitats of frequent (grazing lawns) and infrequent (shrub forest) use by H. amphibius and other grazing herbivores. In contrast to existing hypotheses regarding grazing species, we found that H. amphibius had little effect on local plant species richness. Simultaneous observations of exclosures designed to remove all large herbivores revealed that H. amphibius removal had ecologically significant impacts, but that the removal of all species of large herbivores generated more pronounced impacts than the removal of H. amphibius alone. In aggregate, our results suggest that H. amphibius have myriad effects on their terrestrial habitats that likely improve the quality of forage available for other herbivores. We suggest that ongoing losses of this vulnerable megaherbivore are likely to cause significant ecological change.


Assuntos
Artiodáctilos , Solo , Animais , Ecossistema , Herbivoria , Plantas
5.
Proc Natl Acad Sci U S A ; 115(22): E5028-E5037, 2018 05 29.
Artigo em Inglês | MEDLINE | ID: mdl-29760056

RESUMO

Cross-boundary transfers of nutrients can profoundly shape the ecology of recipient systems. The common hippopotamus, Hippopotamus amphibius, is a significant vector of such subsidies from terrestrial to river ecosystems. We compared river pools with high and low densities of H. amphibius to determine how H. amphibius subsidies shape the chemistry and ecology of aquatic communities. Our study watershed, like many in sub-Saharan Africa, has been severely impacted by anthropogenic water abstraction reducing dry-season flow to zero. We conducted observations for multiple years over wet and dry seasons to identify how hydrological variability influences the impacts of H. amphibius During the wet season, when the river was flowing, we detected no differences in water chemistry and nutrient parameters between pools with high and low densities of H. amphibius Likewise, the diversity and abundance of fish and aquatic insect communities were indistinguishable. During the dry season, however, high-density H. amphibius pools differed drastically in almost all measured attributes of water chemistry and exhibited depressed fish and insect diversity and fish abundance compared with low-density H. amphibius pools. Scaled up to the entire watershed, we estimate that H. amphibius in this hydrologically altered watershed reduces dry-season fish abundance and indices of gamma-level diversity by 41% and 16%, respectively, but appears to promote aquatic invertebrate diversity. Widespread human-driven shifts in hydrology appear to redefine the role of H. amphibius, altering their influence on ecosystem diversity and functioning in a fashion that may be more severe than presently appreciated.


Assuntos
Artiodáctilos/fisiologia , Ecossistema , Eutrofização/fisiologia , Rios/química , Animais , Peixes , Oxigênio/análise , Oxigênio/metabolismo
6.
PLoS One ; 13(5): e0197669, 2018.
Artigo em Inglês | MEDLINE | ID: mdl-29775481

RESUMO

Benthic algae fuel summer food webs in many sunlit rivers, and are hotspots for primary and secondary production and biogeochemical cycling. Concerningly, riverine benthic algal assemblages can become dominated by toxic cyanobacteria, threatening water quality and public health. In the Eel River in Northern California, over a dozen dog deaths have been attributed to cyanotoxin poisonings since 2000. During the summers of 2013-2015, we documented spatial and temporal patterns of cyanotoxin concentrations in the watershed, showing widespread distribution of anatoxin-a in benthic cyanobacterial mats. Solid phase adsorption toxin tracking (SPATT) samplers were deployed weekly to record dissolved microcystin and anatoxin-a levels at 10 sites throughout the watershed, and 187 Anabaena-dominated or Phormidium-dominated cyanobacterial mat samples were collected from 27 locations to measure intracellular anatoxin-a (ATX) and microcystins (MCY). Anatoxin-a levels were higher than microcystin for both SPATT (mean MCY = 0.8 and ATX = 4.8 ng g resin-1 day-1) and cyanobacterial mat samples (mean MCY = 0.074 and ATX = 1.89 µg g-1 DW). Of the benthic mats sampled, 58.9% had detectable anatoxin-a (max = 70.93 µg g-1 DW), while 37.6% had detectable microcystins (max = 2.29 µg g-1 DW). SPATT cyanotoxin levels peaked in mid-summer in warm mainstem reaches of the watershed. This is one of the first documentations of widespread anatoxin-a occurrence in benthic cyanobacterial mats in a North American watershed.


Assuntos
Toxinas Bacterianas/análise , Cianobactérias/isolamento & purificação , Cianobactérias/patogenicidade , Rios/química , Rios/microbiologia , Tropanos/análise , Anabaena/química , Anabaena/isolamento & purificação , Anabaena/patogenicidade , Animais , Toxinas Bacterianas/envenenamento , California , Cianobactérias/química , Cães , Monitoramento Ambiental , Humanos , Microcistinas/análise , Microcistinas/envenenamento , Oscillatoria/química , Oscillatoria/isolamento & purificação , Oscillatoria/patogenicidade , Saúde Pública , Tropanos/envenenamento , Microbiologia da Água , Poluentes Químicos da Água/análise , Poluentes Químicos da Água/envenenamento , Qualidade da Água
7.
Proc Natl Acad Sci U S A ; 114(38): 10155-10159, 2017 09 19.
Artigo em Inglês | MEDLINE | ID: mdl-28874576

RESUMO

Little is known about the importance of food-web processes as controls of river primary production due to the paucity of both long-term studies and of depositional environments which would allow retrospective fossil analysis. To investigate how freshwater algal production in the Eel River, northern California, varied over eight decades, we quantified siliceous shells (frustules) of freshwater diatoms from a well-dated undisturbed sediment core in a nearshore marine environment. Abundances of freshwater diatom frustules exported to Eel Canyon sediment from 1988 to 2001 were positively correlated with annual biomass of Cladophora surveyed over these years in upper portions of the Eel basin. Over 28 years of contemporary field research, peak algal biomass was generally higher in summers following bankfull, bed-scouring winter floods. Field surveys and experiments suggested that bed-mobilizing floods scour away overwintering grazers, releasing algae from spring and early summer grazing. During wet years, growth conditions for algae could also be enhanced by increased nutrient loading from the watershed, or by sustained summer base flows. Total annual rainfall and frustule densities in laminae over a longer 83-year record were weakly and negatively correlated, however, suggesting that positive effects of floods on annual algal production were primarily mediated by "top-down" (consumer release) rather than "bottom-up" (growth promoting) controls.


Assuntos
Clorófitas , Diatomáceas , Ecossistema , Sedimentos Geológicos/análise , Rios , Clima
8.
Harmful Algae ; 66: 79-87, 2017 06.
Artigo em Inglês | MEDLINE | ID: mdl-28602256

RESUMO

Benthic cyanobacteria in rivers produce cyanotoxins and affect aquatic food webs, but knowledge of their ecology lags behind planktonic cyanobacteria. The buoyancy of benthic Anabaena spp. mats was studied to understand implications for Anabaena dispersal in the Eel River, California. Field experiments were used to investigate the effects of oxygen bubble production and dissolution on the buoyancy of Anabaena dominated benthic mats in response to light exposure. Samples of Anabaena dominated mats were harvested from the South Fork Eel River and placed in settling columns to measure floating and sinking velocities, or deployed into in situ ambient and low light treatments to measure the effect of light on flotation. Floating and sinking occurred within minutes and were driven by oxygen bubbles produced during photosynthesis, rather than intracellular changes in carbohydrates or gas vesicles. Light experiment results showed that in a natural ambient light regime, mats remained floating for at least 4days, while in low light mats begin to sink in <24h. Floating Anabaena samples were collected from five sites in the watershed and found to contain the cyanotoxins anatoxin-a and microcystin, with higher concentrations of anatoxin-a (median 560, max 30,693ng/gDW) than microcystin (median 30, max 37ng/gDW). The ability of Anabaena mats to maintain their buoyancy will markedly increase their downstream dispersal distances. Increased buoyancy also allows toxin-containing mats to collect along shorelines, increasing threats to human and animal public health.


Assuntos
Anabaena/fisiologia , Toxinas Bacterianas/análise , Proliferação Nociva de Algas/fisiologia , Rios , California , Luz , Microcistinas/análise , Dinâmica Populacional , Tropanos/análise
10.
Ecology ; 97(11): 2905-2909, 2016 11.
Artigo em Inglês | MEDLINE | ID: mdl-27870047

RESUMO

Robert T. Paine, who passed away on 13 June 2016, is among the most influential people in the history of ecology. Paine was an experimentalist, a theoretician, a practitioner, and proponent of the "ecology of place," and a deep believer in the importance of natural history to ecological understanding. His scientific legacy grew from the discovery of a link between top-down forcing and species diversity, a breakthrough that led to the ideas of both keystone species and trophic cascades, and to our early understanding of the mosaic nature of biological communities, causes of zonation across physical gradients, and the intermediate-disturbance hypothesis of species diversity. Paine's influence as a mentor was equally important to the growth of ecological thinking, natural resource conservation, and policy. He served ecology as an Ecological Society of America president, an editor of the Society's journals, a member of and contributor to the National Academy of Sciences and the National Research Council, and an in-demand advisor to various state and federal agencies. Paine's broad interests, enthusiasm, charisma, and humor deeply affected our lives and the lives of so many others.


Assuntos
Ecologia , Ecologia/história , História do Século XX , Mentores/história , Publicações/história , Pesquisa/história , Estados Unidos
11.
Ecol Lett ; 18(10): 1012-20, 2015 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-26248587

RESUMO

Animal migrations can link ecosystems across space. We discovered an aquatic insect that migrates between a river mainstem and its tributaries, and provides an important trophic subsidy for tributary predators. A mayfly, Ephemerella maculata, rears in a warm, sunlit productive river mainstem, then migrates as adults to cool, shaded unproductive tributaries where they oviposit and die. This migration tripled insect flux into a tributary for 1 month in summer. A manipulative field experiment showed that this E. maculata subsidy nearly tripled the growth of the young of the year steelhead trout (Oncorhynchus mykiss) in the recipient tributary over the summer months, and was more important than terrestrial invertebrate subsidies, which have been considered the primary food source for predators in small, forested creeks. By delivering food subsidies from productive but warming river mainstems to cool but food-limited tributaries, aquatic insect migrations could enhance resilience to cool-water predators in warming river networks.


Assuntos
Migração Animal , Ephemeroptera/fisiologia , Cadeia Alimentar , Oncorhynchus mykiss/crescimento & desenvolvimento , Rios , Animais , California , Ecossistema , Temperatura Ambiente
12.
Bioscience ; 65(8): 822-829, 2015 Aug 01.
Artigo em Inglês | MEDLINE | ID: mdl-26955083

RESUMO

The liberalization of marijuana policies, including the legalization of medical and recreational marijuana, is sweeping the United States and other countries. Marijuana cultivation can have significant negative collateral effects on the environment that are often unknown or overlooked. Focusing on the state of California, where by some estimates 60%-70% of the marijuana consumed in the United States is grown, we argue that (a) the environmental harm caused by marijuana cultivation merits a direct policy response, (b) current approaches to governing the environmental effects are inadequate, and

13.
Environ Sci Technol ; 48(17): 10128-35, 2014 Sep 02.
Artigo em Inglês | MEDLINE | ID: mdl-25105808

RESUMO

Mercury (Hg) is widely distributed in the environment, and its organic form, methylmercury (MeHg), can extensively bioaccumulate and biomagnify in aquatic and terrestrial food webs. Concentrations of MeHg in organisms are highly variable, and the sources in natural food webs are often not well understood. This study examined stable isotope ratios of MeHg (mass-dependent fractionation, as δ(202)HgMeHg; and mass-independent fractionation, as Δ(199)HgMeHg) in benthic invertebrates, juvenile steelhead trout (Oncorhynchus mykiss), and water striders (Gerris remigis) along a stream productivity gradient, as well as carnivorous terrestrial invertebrates, in a forested watershed at the headwater of South Fork Eel River in northern California. Throughout the sampling sites, δ(202)HgMeHg (after correction due to the effect of MeHg photodegradation) was significantly different between benthic (median = -1.40‰; range, -2.34 to -0.78‰; total number of samples = 29) and terrestrial invertebrates (median = +0.51‰; range, -0.37 to +1.40‰; total number of samples = 9), but no major difference between these two groups was found for Δ(199)HgMeHg. Steelhead trout (52 individual fishes) have MeHg of predominantly aquatic origins, with a few exceptions at the upstream locations (e.g., 1 fish collected in a tributary had a purely terrestrial MeHg source and 4 fishes had mixed aquatic and terrestrial MeHg sources). Water striders (seven pooled samples) derive MeHg largely from terrestrial sources throughout headwater sections. These data suggest that direct terrestrial subsidy (e.g., terrestrial invertebrates falling into water) can be important for some stream predators in headwater streams and could represent an important means of transfer of terrestrially derived MeHg (e.g., in situ methylation within forests, atmospheric sources) to aquatic ecosystems. Moreover, these findings show that terrestrial subsidies can enhance MeHg bioaccumulation of consumers in headwater streams where aqueous MeHg levels are very low.


Assuntos
Monitoramento Ambiental , Mercúrio/análise , Compostos de Metilmercúrio/análise , Comportamento Predatório , Rios , Poluentes Químicos da Água/análise , Animais , Biota , California , Fracionamento Químico , Comportamento Alimentar , Cadeia Alimentar , Invertebrados/metabolismo , Isótopos de Mercúrio/análise , Truta/metabolismo
14.
Proc Natl Acad Sci U S A ; 111(2): 581-4, 2014 Jan 14.
Artigo em Inglês | MEDLINE | ID: mdl-24367087

RESUMO

Overfishing and environmental change have triggered many severe and unexpected consequences. As existing communities have collapsed, new ones have become established, fundamentally transforming ecosystems to those that are often less productive for fisheries, more prone to cycles of booms and busts, and thus less manageable. We contend that the failure of fisheries science and management to anticipate these transformations results from a lack of appreciation for the nature, strength, complexity, and outcome of species interactions. Ecologists have come to understand that networks of interacting species exhibit nonlinear dynamics and feedback loops that can produce sudden and unexpected shifts. We argue that fisheries science and management must follow this lead by developing a sharper focus on species interactions and how disrupting these interactions can push ecosystems in which fisheries are embedded past their tipping points.


Assuntos
Ecossistema , Pesqueiros/métodos , Biologia Marinha/métodos , Pesqueiros/legislação & jurisprudência , Biologia Marinha/tendências , Dinâmica não Linear , Dinâmica Populacional , Especificidade da Espécie
15.
Am Nat ; 181 Suppl 1: S76-99, 2013 May.
Artigo em Inglês | MEDLINE | ID: mdl-23598361

RESUMO

Living nature can be thought of as a tapestry, defined not only by its constituent parts but also by how these parts are woven together. The weaving of this tapestry is a metaphor for species interactions, which can be divided into three broad classes: competitive, mutualistic, and consumptive. Direct interactions link together as more complex networks, for example, the joining of consumptive interactions into food webs. Food web dynamics are driven, in turn, by changes in the abundances of web members, whose numbers or biomass respond to bottom-up (resource limitation) and top-down (consumer limitation) forcing. The relative strengths of top-down and bottom-up forcing on the abundance of a given web member depend on its ecological context, including its topological position within the food web. Top-down effects by diverse consumers are nearly ubiquitous, in many cases influencing the structure and operation of ecosystems. While the ecological effects of such interactions are well known, far less is known of their evolutionary consequences. In this essay, we describe sundry consequences of these interaction chains on species and ecosystem processes, explain several known or suspected evolutionary effects of consumer-induced interaction chains, and identify areas where reciprocity between ecology and evolution involving the indirect effects of consumer-prey interaction chains might be further explored.


Assuntos
Evolução Biológica , Cadeia Alimentar , África , Previsões/métodos , Rios , Simbiose , Estados Unidos
16.
Conserv Biol ; 26(3): 513-24, 2012 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-22594596

RESUMO

Widespread alteration of natural hydrologic patterns by large dams combined with peak demands for power and water delivery during summer months have resulted in frequent aseasonal flow pulses in rivers of western North America. Native species in these ecosystems have evolved with predictable annual flood-drought cycles; thus, their likelihood of persistence may decrease in response to disruption of the seasonal synchrony between stable low-flow conditions and reproduction. We evaluated whether altered flow regimes affected 2 native frogs in California and Oregon (U.S.A.) at 4 spatial and temporal extents. We examined changes in species distribution over approximately 50 years, current population density in 11 regulated and 16 unregulated rivers, temporal trends in abundance among populations occupying rivers with different hydrologic histories, and within-year patterns of survival relative to seasonal hydrology. The foothill yellow-legged frog (Rana boylii), which breeds only in flowing water, is more likely to be absent downstream of large dams than in free-flowing rivers, and breeding populations are on average 5 times smaller in regulated rivers than in unregulated rivers. Time series data (range = 8 - 19 years) from 5 populations of yellow-legged frogs and 2 populations of California red-legged frogs (R. draytonii) across a gradient of natural to highly artificial timing and magnitude of flooding indicate that variability of flows in spring and summer is strongly correlated with high mortality of early life stages and subsequent decreases in densities of adult females. Flow management that better mimics natural flow timing is likely to promote persistence of these species and others with similar phenology.


Assuntos
Conservação dos Recursos Naturais , Ecossistema , Ranidae/fisiologia , Movimentos da Água , Animais , California , Dinâmica Populacional , Ranidae/crescimento & desenvolvimento , Rios , Estações do Ano , Especificidade da Espécie
17.
PLoS Biol ; 10(1): e1001247, 2012 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-22291572

RESUMO

Wetlands are among the most productive and economically valuable ecosystems in the world. However, because of human activities, over half of the wetland ecosystems existing in North America, Europe, Australia, and China in the early 20th century have been lost. Ecological restoration to recover critical ecosystem services has been widely attempted, but the degree of actual recovery of ecosystem functioning and structure from these efforts remains uncertain. Our results from a meta-analysis of 621 wetland sites from throughout the world show that even a century after restoration efforts, biological structure (driven mostly by plant assemblages), and biogeochemical functioning (driven primarily by the storage of carbon in wetland soils), remained on average 26% and 23% lower, respectively, than in reference sites. Either recovery has been very slow, or postdisturbance systems have moved towards alternative states that differ from reference conditions. We also found significant effects of environmental settings on the rate and degree of recovery. Large wetland areas (>100 ha) and wetlands restored in warm (temperate and tropical) climates recovered more rapidly than smaller wetlands and wetlands restored in cold climates. Also, wetlands experiencing more (riverine and tidal) hydrologic exchange recovered more rapidly than depressional wetlands. Restoration performance is limited: current restoration practice fails to recover original levels of wetland ecosystem functions, even after many decades. If restoration as currently practiced is used to justify further degradation, global loss of wetland ecosystem function and structure will spread.


Assuntos
Conservação dos Recursos Naturais/tendências , Recuperação e Remediação Ambiental/tendências , Áreas Alagadas , Animais , Austrália , Biodiversidade , Carbono/química , China , Clima , Bases de Dados Bibliográficas , Recuperação e Remediação Ambiental/métodos , Europa (Continente) , América do Norte , Plantas , Solo/química , Ondas de Maré , Vertebrados , Ciclo Hidrológico
18.
Science ; 333(6040): 301-6, 2011 Jul 15.
Artigo em Inglês | MEDLINE | ID: mdl-21764740

RESUMO

Until recently, large apex consumers were ubiquitous across the globe and had been for millions of years. The loss of these animals may be humankind's most pervasive influence on nature. Although such losses are widely viewed as an ethical and aesthetic problem, recent research reveals extensive cascading effects of their disappearance in marine, terrestrial, and freshwater ecosystems worldwide. This empirical work supports long-standing theory about the role of top-down forcing in ecosystems but also highlights the unanticipated impacts of trophic cascades on processes as diverse as the dynamics of disease, wildfire, carbon sequestration, invasive species, and biogeochemical cycles. These findings emphasize the urgent need for interdisciplinary research to forecast the effects of trophic downgrading on process, function, and resilience in global ecosystems.


Assuntos
Ecossistema , Extinção Biológica , Cadeia Alimentar , Animais , Biodiversidade , Comportamento Alimentar , Humanos , Espécies Introduzidas , Dinâmica Populacional , Comportamento Predatório
19.
Ecology ; 92(1): 140-50, 2011 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-21560684

RESUMO

The elemental composition of solutes transported by rivers reflects combined influences of surrounding watersheds and transformations within stream networks, yet comparatively little is known about downstream changes in effects of watershed loading vs. in-channel processes. In the forested watershed of a river under a mediterranean hydrologic regime, we examined the influence of longitudinal changes in environmental conditions on water-column nutrient composition during summer base flow across a network of sites ranging from strongly heterotrophic headwater streams to larger, more autotrophic sites downstream. Small streams (0.1-10 km2 watershed area) had longitudinally similar nutrient concentration and composition with low (approximately 2) dissolved nitrogen (N) to phosphorus (P) ratios. Abrupt deviations from this pattern were observed in larger streams with watershed areas > 100 km2 where insolation and algal abundance and production rapidly increased. Downstream, phosphorus and silica concentrations decreased by > 50% compared to headwater streams, and dissolved organic carbon and nitrogen increased by approximately 3-6 times. Decreasing dissolved P and increasing dissolved N raised stream-water N:P to 46 at the most downstream sites, suggesting a transition from N limitation in headwaters to potential P limitation in larger channels. We hypothesize that these changes were mediated by increasing algal photosynthesis and N fixation by benthic algal assemblages, which, in response to increasing light availability, strongly altered stream-water nutrient concentration and stoichiometry in larger streams and rivers.


Assuntos
Ecossistema , Rios , Água/química , California , Luz , Movimentos da Água
20.
ISME J ; 4(4): 520-30, 2010 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-20033068

RESUMO

Acid mine drainage (AMD), an extreme environment characterized by low pH and high metal concentrations, can support dense acidophilic microbial biofilm communities that rely on chemoautotrophic production based on iron oxidation. Field determined production rates indicate that, despite the extreme conditions, these communities are sufficiently well adapted to their habitats to achieve primary production rates comparable to those of microbial communities occurring in some non-extreme environments. To enable laboratory studies of growth, production and ecology of AMD microbial communities, a culturing system was designed to reproduce natural biofilms, including organisms recalcitrant to cultivation. A comprehensive metabolic labeling-based quantitative proteomic analysis was used to verify that natural and laboratory communities were comparable at the functional level. Results confirmed that the composition and core metabolic activities of laboratory-grown communities were similar to a natural community, including the presence of active, low abundance bacteria and archaea that have not yet been isolated. However, laboratory growth rates were slow compared with natural communities, and this correlated with increased abundance of stress response proteins for the dominant bacteria in laboratory communities. Modification of cultivation conditions reduced the abundance of stress response proteins and increased laboratory community growth rates. The research presented here represents the first description of the application of a metabolic labeling-based quantitative proteomic analysis at the community level and resulted in a model microbial community system ideal for testing physiological and ecological hypotheses.


Assuntos
Archaea/crescimento & desenvolvimento , Archaea/metabolismo , Bactérias/crescimento & desenvolvimento , Bactérias/metabolismo , Biofilmes/crescimento & desenvolvimento , Microbiologia Ambiental , Proteoma/análise , Ácidos/metabolismo , Ferro/metabolismo , Oxirredução
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