Search

Sustainable ecosystem management relies on our ability to predict changes in plant diversity and to understand the underlying mechanisms. Empirical evidence demonstrates that abundance- and functional-based processes simultaneously explain the loss of plant diversity in response to human activities. Recently, a novel indicator based on percent cover (CoverD) and maximum height (HeightD) of the dominant plant species – space resource utilization (SRUD) – has proven to give robust and better predictions of plant diversity dynamics than community biomass. Whether the superior predictive ability of SRUD is due to its capacity to simultaneously capture abundance- and functional-based processes remains unknown. Here, we tested this hypothesis by quantifying mechanistic links between changes in SRUD and biodiversity in response to nutrients and herbivores. Furthermore, we assessed the relative contribution of dominant, intermediate and rare species to reduced density of individuals by combining null model analysis with field experiments. We found that SRUD successfully captured changes in ground-level light availability and changes in the number of individuals to predict plant diversity dynamics, and each of CoverD and HeightD partly and independently contributed to both processes. Comparative results from null model analysis and field experiments confirmed that individual losses of dominant, intermediate and rare species followed non-random processes. Specifically, compared with random loss process, rare species lost proportionally more individuals and thus disproportionately contributed to species loss, while dominant and intermediate species lost less. Our results demonstrate that SRUD captures both abundance- and functional-based processes thus explaining why SRUD provides more accurate predictions of changes in species diversity. Given that rare species can play an important role in shaping community structure, resisting against invasion, impacting higher trophic levels and providing multiple ecosystem functions, reducing the SRU of dominant species could alleviate the risk of exclusion of rare species by mitigating abundance- and functional-based competition processes.

Anthropogenic nutrient enrichment is driving global biodiversity decline and modifying ecosystem functions. Theory suggests that plant functional types that fix atmospheric nitrogen have a competitive advantage in nitrogen-poor soils, but lose this advantage with increasing nitrogen supply. By contrast, the addition of phosphorus, potassium, and other nutrients may benefit such species in low-nutrient environments by enhancing their nitrogen-fixing capacity. We present a global-scale experiment confirming these predictions for nitrogen-fixing legumes (Fabaceae) across 45 grasslands on six continents. Nitrogen addition reduced legume cover, richness, and biomass, particularly in nitrogen-poor soils, while cover of non-nitrogen-fixing plants increased. The addition of phosphorous, potassium, and other nutrients enhanced legume abundance, but did not mitigate the negative effects of nitrogen addition. Increasing nitrogen supply thus has the potential to decrease the diversity and abundance of grassland legumes worldwide regardless of the availability of other nutrients, with consequences for biodiversity, food webs, ecosystem resilience, and genetic improvement of protein-rich agricultural plant species.

Soil nitrogen (N) availability is critical for grassland functioning. However, human activities have increased the supply of biologically limiting nutrients, and changed the density and identity of mammalian herbivores. These anthropogenic changes may alter net soil N mineralization (soil net Nmin), that is, the net balance between N mineralization and immobilization, which could severely impact grassland structure and functioning. Yet, to date, little is known about how fertilization and herbivore removal individually, or jointly, affect soil net Nmin across a wide range of grasslands that vary in soil and climatic properties. Here we collected data from 22 grasslands on five continents, all part of a globally replicated experiment, to assess how fertilization and herbivore removal affected potential (laboratory‐based) and realized (field‐based) soil net Nmin. Herbivore removal in the absence of fertilization did not alter potential and realized soil net Nmin. However, fertilization alone and in combination with herbivore removal consistently increased potential soil net Nmin. Realized soil net Nmin, in contrast, significantly decreased in fertilized plots where herbivores were removed. Treatment effects on potential and realized soil net Nmin were contingent on site‐specific soil and climatic properties. Fertilization effects on potential soil net Nmin were larger at sites with higher mean annual precipitation (MAP) and temperature of the wettest quarter (T.q.wet). Reciprocally, realized soil net Nmin declined most strongly with fertilization and herbivore removal at sites with lower MAP and higher T.q.wet. In summary, our findings show that anthropogenic nutrient enrichment, herbivore exclusion and alterations in future climatic conditions can negatively impact soil net Nmin across global grasslands under realistic field conditions. This is an important context‐dependent knowledge for grassland management worldwide.

Microbial processing of aggregate-unprotected organic matter inputs is key for soil fertility, long-term ecosystem carbon and nutrient sequestration and sustainable agriculture. We investigated the effects of adding multiple nutrients (nitrogen, phosphorus and potassium plus nine essential macro- and micro-nutrients) on decomposition and biochemical transformation of standard plant materials buried in 21 grasslands from four continents. Addition of multiple nutrients weakly but consistently increased decomposition and biochemical transformation of plant remains during the peak-season, concurrent with changes in microbial exoenzymatic activity. Higher mean annual precipitation and lower mean annual temperature were the main climatic drivers of higher decomposition rates, while biochemical transformation of plant remains was negatively related to temperature of the wettest quarter. Nutrients enhanced decomposition most at cool, high rainfall sites, indicating that in a warmer and drier future fertilized grassland soils will have an even more limited potential for microbial processing of plant remains. Fil: Ochoa Hueso, Raúl. Universidad de Cádiz; España Fil: Borer, Elizabeth. University of Minnesota; Estados Unidos Fil: Seabloom, Eric. University of Minnesota; Estados Unidos Fil: Hobbie, Sarah E.. University of Minnesota; Estados Unidos Fil: Risch, Anita C.. Swiss Federal Institute for Forest, Snow and Landscape Research; Suiza Fil: Collins, Scott L.. University of New Mexico; Estados Unidos Fil: Alberti, Juan. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; Argentina Fil: Bahamonde, Héctor Alejandro. Universidad Nacional de la Patagonia Austral; Argentina. Instituto Nacional de Tecnología Agropecuaria; Argentina Fil: Brown, Cynthia S.. State University of Colorado - Fort Collins; Estados Unidos Fil: Caldeira, Maria C.. Universidade Nova de Lisboa; Portugal Fil: Daleo, Pedro. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; Argentina Fil: Dickman, Chris R.. University of Sydney; Australia Fil: Ebeling, Anne. Universitat Jena; Alemania Fil: Eisenhauer, Nico. German Centre for Integrative Biodiversity Research; Alemania. Universitat Leipzig; Alemania Fil: Esch, Ellen H.. University Of Guelph. Department Of Integrative Biology.; Canadá Fil: Eskelinen, Anu. German Centre for Integrative Biodiversity Research; Alemania. Helmholtz Centre for Environmental Research; Alemania. University of Oulu; Finlandia Fil: Fernández, Victoria. Universidad Politécnica de Madrid; España Fil: Güsewell, Sabine. Institute of Integrative Biology; Suiza Fil: Gutierrez Larruga, Blanca. Universidad Autónoma de Madrid; España Fil: Hofmockel, Kirsten. Pacific Northwest National Laboratory; Estados Unidos. University of Iowa; Estados Unidos Fil: Laungani, Ramesh. Doane University; Estados Unidos Fil: Lind, Eric. University of Minnesota; Estados Unidos Fil: López, Andrea. University of New Mexico; Estados Unidos Fil: McCulley, Rebecca L.. University of Kentucky; Estados Unidos Fil: Moore, Joslin L.. Monash University; Australia Fil: Peri, Pablo Luis. Instituto Nacional de Tecnología Agropecuaria; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro de Investigaciones y Transferencia de Santa Cruz. Universidad Tecnológica Nacional. Facultad Regional Santa Cruz. Centro de Investigaciones y Transferencia de Santa Cruz. Universidad Nacional de la Patagonia Austral. Centro de Investigaciones y Transferencia de Santa Cruz; Argentina Fil: Power, Sally A.. University of Western Sydney; Australia Fil: Price, Jodi N.. Charles Sturt University; Australia Fil: Prober, Suzanne M.. Csiro National Collections And Marine Infrastructure; Australia Fil: Roscher, Christiane. German Centre for Integrative Biodiversity Research; Alemania. University of Oulu; Finlandia Fil: Velasco Ayuso, Sergio. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura; Argentina

The accumulation of live and dead trees and other vegetation in forests across the western United States is producing larger and more severe wildfires. To decrease wildfire severity and increase forest resilience, foresters regularly remove excess fuel by burning woody material in piles. This common practice could also cause persistent ecosystem changes such as the alteration of soil physical and chemical properties due to extreme soil heating, which can favor invasion by non-native plant species. The abundance and species richness of native plant communities may also remain depressed for many years after burning has removed vegetation and diminished propagules in the soil. This adds to the vulnerability of burned areas to the colonization and dominance by invasive species. Research into the use of revegetation techniques following pile burning to suppress invasion is limited. Studies conducted in various woodland types that investigated revegetation of pile burn scars have met with varying success. To assess the effectiveness of restoring pile burn scars in Rocky Mountain National Park, Colorado, we monitored vegetation in 26 scars, each about 5 m in diameter, the growing season after burning. Later that summer, we selected 14 scars for restoration that included soil scarification, seed addition, and pine duff mulch cover. We monitored the scars for four years, pre-restoration, and three years post-restoration and found that the cover of seeded species exceeded the surrounding unburned areas and unseeded controls. The restoration seeding suppressed cover of non-native species as well as native species that were not seeded during restoration. Our results suggest that restoration of pile burn scars could be a useful tool to retard the establishment of invasive plant species when there are pre-existing infestations near scars. However, this must be weighed against the simultaneous suppression of native species recruitment. Monitoring for periods more than three years will help us understand how long the suppression of native and non-native species by restoration species may persist.

Evaluating the conditions where a species can persist is an important question in ecology both to understand tolerances of organisms and to predict distributions across landscapes. Presence data combined with background or pseudo-absence locations are commonly used with species distribution modeling to develop these relationships. However, there is not a standard method to generate background or pseudo-absence locations, and method choice affects model outcomes. We evaluated combinations of both model algorithms (simple and complex generalized linear models, multivariate adaptive regression splines, Maxent, boosted regression trees, and random forest) and background methods (random, minimum convex polygon, and continuous and binary kernel density estimator (KDE)) to assess the sensitivity of model outcomes to choices made. We evaluated six questions related to model results, including five beyond the common comparison of model accuracy assessment metrics (biological interpretability of response curves, cross-validation robustness, independent data accuracy and robustness, and prediction consistency). For our case study with cheatgrass in the western US, random forest was least sensitive to background choice and the binary KDE method was least sensitive to model algorithm choice. While this outcome may not hold for other locations or species, the methods we used can be implemented to help determine appropriate methodologies for particular research questions.

Soil nitrogen mineralisation (Nmin), the conversion of organic into inorganic N, is important for productivity and nutrient cycling. The balance between mineralisation and immobilisation (net Nmin) varies with soil properties and climate. However, because most global-scale assessments of net Nmin are laboratory-based, its regulation under field-conditions and implications for real-world soil functioning remain uncertain. Here, we explore the drivers of realised (field) and potential (laboratory) soil net Nmin across 30 grasslands worldwide. We find that realised Nmin is largely explained by temperature of the wettest quarter, microbial biomass, clay content and bulk density. Potential Nmin only weakly correlates with realised Nmin, but contributes to explain realised net Nmin when combined with soil and climatic variables. We provide novel insights of global realised soil net Nmin and show that potential soil net Nmin data available in the literature could be parameterised with soil and climate data to better predict realised Nmin., Nitrogen mineralisation (Nmin), an important index of soil fertility, is often determined in the laboratory, with an uncertain relationship to Nmin under field conditions. Here the authors show that combining laboratory measurements with environmental data greatly improves predictions of field Nmin at a global scale.

Within a species, the distance travelled by a particular diaspore depends on its morphology. In Poaceae, the presence of terminal sterile florets can lead to diaspore heteromorphism, which may influence dispersal. We tested the hypothesis that the presence of sterile florets favored dispersal in Bromus tectorum L., an invasive grass in the Western US. We used field and controlled experiments to study the dispersal of caryopses with and without sterile florets attached (respectively complex and simple diaspores), as well as pieces of inflorescence that detached from the mother plants. We considered both primary and secondary dispersal, as well as abiotic and biotic dispersal agents. The distance travelled by the diaspores and their attachment to animal fur were related to the presence and number of sterile florets. Abiotic agents moved diaspores over relatively short distances, both in terms of primary and secondary dispersal. A significant proportion of diaspores attached to fur, suggesting a potential for dispersal over long distances. Complex diaspores were better dispersers than simple ones (and pieces of inflorescence), and this pattern was consistent across the study. However, among complex diaspores, the number of sterile florets had little or no influence. Considering primary and secondary dispersal by abiotic and biotic agents provided a general picture of the dispersal ecology of B. tectorum . For all the dispersal steps and dispersal agents we studied, the presence of sterile florets favored dispersal. These results highlight the functional significance of diaspore heteromorphism induced by floret sterility in the dispersal of Poaceae.

Aboveground net primary production (ANPP) is a key integrator of C uptake and energy flow in many terrestrial ecosystems. As such, ecologists have long sought to understand the factors driving variation in this important ecosystem process. Although total annual precipitation has been shown to be a strong predictor of ANPP in grasslands across broad spatial scales, it is often a poor predictor at local scales. Here we examine the amount of variation in ANPP that can be explained by total annual precipitation versus precipitation during specific periods of the year (precipitation periods) and nutrient availability at three sites representing the major grassland types (shortgrass steppe, mixed-grass prairie, and tallgrass prairie) spanning the broad precipitation gradient of the U.S. Central Great Plains. Using observational data, we found that precipitation periods and nutrient availability were much stronger predictors of site-level ANPP than total annual precipitation. However, the specific nutrients and precipitation periods that best predicted ANPP differed among the three sites. These effects were mirrored experimentally at the shortgrass and tallgrass sites, with precipitation and nutrient availability co-limiting ANPP, but not at the mixed-grass site, where nutrient availability determined ANPP exclusive of precipitation effects. Dominant grasses drove the ANPP response to increased nutrient availability at all three sites. However, the relative responses of rare grasses and forbs were greater than those of the dominant grasses to experimental nutrient additions, thus potentially driving species turnover with chronic nutrient additions. This improved understanding of the factors driving variation in ANPP within ecosystems spanning the broad precipitation gradient of the Great Plains will aid predictions of alterations in ANPP under future global change scenarios.

Alien grass invasions in arid and semi-arid ecosystems are resulting in grass–fire cycles and ecosystem-level transformations that severely diminish ecosystem services. Our capacity to address the rapid and complex changes occurring in these ecosystems can be enhanced by developing an understanding of the environmental factors and ecosystem attributes that determine resilience of native ecosystems to stress and disturbance, and resistance to invasion. Cold desert shrublands occur over strong environmental gradients and exhibit significant differences in resilience and resistance. They provide an excellent opportunity to increase our understanding of these concepts. Herein, we examine a series of linked questions about (a) ecosystem attributes that determine resilience and resistance along environmental gradients, (b) effects of disturbances like livestock grazing and altered fire regimes and of stressors like rapid climate change, rising CO2, and N deposition on resilience and resistance, and (c) interacting effects of resilience and resistance on ecosystems with different environmental conditions. We conclude by providing strategies for the use of resilience and resistance concepts in a management context. At ecological site scales, state and transition models are used to illustrate how differences in resilience and resistance influence potential alternative vegetation states, transitions among states, and thresholds. At landscape scales management strategies based on resilience and resistance—protection, prevention, restoration, and monitoring and adaptive management—are used to determine priority management areas and appropriate actions.

Pan et al . claim that our results actually support a strong linear positive relationship between productivity and richness, whereas Fridley et al . contend that the data support a strong humped relationship. These responses illustrate how preoccupation with bivariate patterns distracts from a deeper understanding of the multivariate mechanisms that control these important ecosystem properties.

Particularly well-known among the many impacts of the invasive annual grass downy brome (Bromus tectorum, Poaceae) is its ability to alter fire cycles and increase in abundance after fire. However, little is known about how fire influences B. tectorum dispersal. We quantified fire effects on B. tectorum dispersal using three recently burned areas in the western region of the Colorado Rocky Mountains by marking diaspores (seeds) with fluorescent powder, and then recovering them at night using ultraviolet lights. Diaspores were of two types: with and without sterile florets attached. We also characterized vegetation cover and near-surface wind speed in burned and unburned areas. Diaspores travelled much farther in burned areas than in nearby unburned areas (mean ± standard error at the end of the experiment: 209 ± 16 cm and 38 ± 1 cm, respectively; maximal distance at the end of the experiment: 2,274 cm and 150 cm, respectively), indicating an increase in dispersal distance after fire. Diaspores with sterile florets attached dispersed longer distances than those without sterile florets (mean ± standard error at the end of the experiment: 141 ± 14 cm and 88 ± 7 cm, respectively). Vegetation cover was lower and wind speeds were higher in the burned areas. Our results indicate that at least one of the mechanisms by which the spread of B. tectorum is promoted by fire is through increased seed dispersal distance. Preventing movement of seeds from nearby infestations into burned areas may help avoid the rapid population expansion often observed.

Russian olive (Elaeagnus angustifolia L.), a Eurasian tree now abundant along rivers in western North America, has an apparent southern distribution limit running through southern California, Arizona, New Mexico and Texas. We used field observations to precisely define this limit in relation to temperature variables. We then investigated whether lack of cold temperatures south of the limit may prevent the accumulation of sufficient chilling, inhibiting dormancy loss of seeds and buds. We found that Russian olive occurrence was more strongly associated with low winter temperatures than with high summer temperatures, and results of controlled seed germination and vegetative bud-break experiments suggest that the chilling requirements for germination and bud-break are partly responsible for the southern range limit. Both seed germination proportion and germination time decreased under conditions simulating those south of the range limit. Similarly, percentage bud break decreased when chilling dropped below values typical of the range limit. In 17–65% of the years from 1980 to 2000, the chilling accumulated at a site near the range limit (El Paso, TX) would lead to a 10% or more decrease in bud-break. The potential decline in growth could have large fitness consequences for Russian olive. If climate change exhibits a warming trend, our results suggest the chilling requirement for bud-break of Russian olive trees will not be met in some years and its southern range limit may retreat northward.

Chemical restrictions, ecological concerns, liability issues, and public sentiment present challenges to land managers attempting to control highly invasive plants like Canada thistle (Cirsium arvense [L.] Scop.). Although herbicide application can be an effective control strategy, increasing limitations force managers of sensitive environments (e.g., national parks, wildlife refuges, protected water-bodies or waterways) to search for effective control alternatives. A greenhouse study was conducted to test the effectiveness of clipping (to simulate field mowing) and grass seeding as alternatives for Canada thistle control. Two native North American grasses (western wheatgrass [Pascopyrum smithii {Rydb.} A. L?ve] and streambank wheatgrass [Elymus lanceolatus {Scribn. & J.G. Sm.}Gould ssp. lanceolatus]) and one sterile hybrid cross between common wheat (Triticum aestivum L.) and tall wheatgrass (Thinopyrum ponticum [Podp.] Z.W. Liu & R.C. Wang) called RegreenTM were used. The effects of clipping and grass seeding on Canada thistle growth, and the effect of Canada thistle on grass growth, were evaluated using 14 unique treatments applied to potted Canada thistle and grass plants. Clipping inhibited Canada thistle growth (by 60%), while grass seeding had no effect. Presence of Canada thistle inhibited grass growth for all seeding treatments except when RegreenTM and western wheatgrass were seeded together with Canada thistle. Planting multiple species for restoration of Canada thistle-infested sites may be important (RegreenTM + western wheatgrass treatment), and cutting Canada thistle may be useful for reducing its growth in restored areas.

Many ecosystems worldwide are dominated by introduced plant species, leading to loss of biodiversity and ecosystem function. A common but rarely tested assumption is that these plants are more abundant in introduced vs. native communities, because ecological or evolutionary-based shifts in populations underlie invasion success. Here, data for 26 herbaceous species at 39 sites, within eight countries, revealed that species abundances were similar at native (home) and introduced (away) sites – grass species were generally abundant home and away, while forbs were low in abundance, but more abundant at home. Sites with six or more of these species had similar community abundance hierarchies, suggesting that suites of introduced species are assembling similarly on different continents. Overall, we found that substantial changes to populations are not necessarily a pre-condition for invasion success and that increases in species abundance are unusual. Instead, abundance at home predicts abundance away, a potentially useful additional criterion for biosecurity programmes.

High-impact biological invasions often involve establishment and spread in disturbed, high-resource patches followed by establishment and spread in biotically or abiotically stressful areas. Evolutionary change may be required for the second phase of invasion (establishment and spread in stressful areas) to occur. When species have low genetic diversity and short selection history, withingeneration phenotypic plasticity is often cited as the mechanism through which spread across multiple habitat types can occur. We show that trans-generational plasticity (TGP) can result in pre-adapted progeny that exhibit traits associated with increased fitness both in high-resource patches and in stressful conditions. In the invasive sedge, Cyperus esculentus, maternal plants growing in nutrient-poor patches can place disproportional number of propagules into nutrient-rich patches. Using the invasive annual grass, Aegilops triuncialis ,w e show that maternal response to soil conditions can confer greater stress tolerance in seedlings in the form of greater photosynthetic efficiency. We also show TGP for a phenological shift in a low resource environment that results in greater stress tolerance in progeny. These lines of evidence suggest that the maternal environment can have profound effects on offspring success and that TGP may play a significant role in some plant invasions.

In recent decades, a growing number of studies have addressed connections between ecological and evolutionary concepts in biologic invasions. These connections may be crucial for understanding the processes underlying invaders’ success. However, the extent to which scientists have worked on the integration of the ecology and evolution of invasive plants is poorly documented, as few attempts have been made to evaluate these efforts in invasion biology research. Such analysis can facilitate recognize well-documented relationships and identify gaps in our knowledge. In this study, we used a network-based method for visualizing the connections between major aspects of ecology and evolution in the primary research literature. Using the family Poaceae as an example, we show that ecological concepts were more studied and better interconnected than were evolutionary concepts. Several possible connections were not documented at all, representing knowledge gaps between ecology and evolution of invaders. Among knowledge gaps, the concepts of plasticity, gene flow, epigenetics and human influence were particularly under-connected. We discuss five possible research avenues to better understand the relationships between ecology and evolution in the success of Poaceae, and of alien plants in general.

At two field sites that differed in fertility, we investigated how species richness, functional group diversity, and species composition of constructed plant communities influenced invasion. Grassland communities were constructed to be either functionally diverse or functionally simple based on belowground resource use patterns of constituent species. Communities were also constructed with different numbers of species (two or five) to examine interactions between species richness, functional diversity and invasion resistance. We hypothesized that communities with more complementary belowground resource use (i.e., more species rich and more functionally diverse communities) would be less easily invaded than communities with greater degrees of belowground resource use overlap. Two contrasting invasive species were introduced: an early-season, shallow rooting annual grass, Bromus hordeaceus (soft chess), and a late-season, deep rooting annual forb, Centaurea solstitialis (yellow starthistle). Invader responses to species richness and functional diversity treatments differed between sites. In general, the more similar the patterns of belowground resource use between residents of the plant community and the invader, the poorer the invader’s performance. Complementarity or overlap of resource use among species in the constructed communities appeared to affect invader success less than complementarity or overlap of resource use between the invader and the species present in the community.

The invasion of 40 million hectares of the American West by cheatgrass (Bromus tectorum L.) has caused widespread modifications in the vegetation of semi-arid ecosystems and increased the frequency of fires. In addition to well-understood mechanisms by which cheatgrass gains competitive advantage, it has been implicated in reducing arbuscular mycorrhizal fungi (AMF) abundance and taxa diversity. We evaluated this possibility at a high elevation site in a two-pronged approach. To test whether cheatgrass changed native AMF communities in ways that affected subsequent native plant growth, we grew cheatgrass and native plants in native soils and then planted native plants into these soils in a greenhouse experiment. We found that cheatgrass-influenced soils did not inhibit native plant growth or AMF sporulation or colonization. To test whether soils in cheatgrass-dominated areas inhibited establishment and growth of native plants, cheatgrass was removed and six seeding combinations were applied. We f...

Fraser et al. (Reports, 17 July 2015, p. 302) report a unimodal relationship between productivity and species richness at regional and global scales, which they contrast with the results of Adler et al. (Reports, 23 September 2011, p. 1750). However, both data sets, when analyzed correctly, show clearly and consistently that productivity is a poor predictor of local species richness. EEA Santa Cruz Fil: Tredennick, Andrew T. Utah State University. Department of Wildland Resources and the Ecology Center; Estados Unidos Fil: Adler, Peter B. Utah State University. Department of Wildland Resources and the Ecology Center; Estados Unidos Fil: Grace, James B. U.S. Geological Survey, Wetland and Aquatic Research Center; Estados Unidos Fil: Harpole, W. Stanley. Helmholtz Center for Environmental Research – UFZ. Department of Physiological Diversity; Alemania Fil: Borer, Elizabeth T. University of Minnesota. Department of Ecology, Evolution, and Behavior; Estados Unidos Fil: Seabloom, Eric W. University of Minnesota. Department of Ecology, Evolution, and Behavior; Estados Unidos Fil: Anderson, T. Michael. Wake Forest University. Department of Biology; Estados Unidos Fil: Bakker, Jonathan D. University of Washington. School of Environmental and Forest Sciences; Estados Unidos Fil: Biederman, Lori A. lowa State University Ecology. Evolution and Organismal Biology; Estados Unidos Fil: Brown, Cynthia S. Colorado State University. Department of Bioagricultural Sciences and Pest Management; Estados Unidos Fil: Buckley, Yvonne M. University of Dublin. School of Natural Sciences. Trinity College Dublin. Zoology; Irlanda. Fil: Chu, Chengjin. Sun Yat-sen University. School of Life Sciences; China. Fil: Collins, Scott L. University of New Mexico. Department of Biology; Estados Unidos Fil: Crawley, Michael J. Imperial College London. Department of Biology; Reino Unido Fil: Fay, Philip A. USDA-ARS. Grassland, Soil, and Water Research Laboratory; Estados Unidos Fil: Firn, Jennifer. Queensland University of Technology. School of Earth, Environmental and Biological Sciences; Australia. Fil: Gruner, Daniel S. University of Maryland. Department of Entomology. Plant Sciences; Estados Unidos Fil: Hagenah, Nicole. University of KwaZulu-Natal. School of Life Sciences; Sudáfrica Fil: Hautier, Yann. Utrecht University. Department of Biology, Ecology and Biodiversity group; Países Bajos Fil: Hector, Andy. University of Oxford. Department of Plant Sciences; Reino Unido Fil: Hillebrand, Helmut. Carl-von-Ossietzky University. Institute for Chemistry and Biology of the Marine Environment; Alemania Fil: Kirkman, Kevin. University of KwaZulu-Natal. School of Life Sciences; Sudáfrica Fil: Knops, Johannes M. H. University of Nebraska. School of Biological Sciences; Estados Unidos Fil: Laungani, Ramesh. Doane College. Biology Department; Estados Unidos Fil: Lind, Eric M. University of Minnesota. Department of Ecology, Evolution and Behavior; Estados Unidos. Fil: MacDougall, Andrew S. University of Guelph. Department of Integrative Biology; Canadá. Fil: McCulley, Rebecca L. University of Kentucky. Department of Plant and Soil Science; Estados Unidos Fil: Mitchell, Charles E. University of North Carolina at Chapel Hill. Department of Biology; Estados Unidos Fil: Moore, Joslin L. Monash University. School of Biological Sciences; Australia. Fil: Morgan, John W. La Trobe University. Department of Ecology, Environment and Evolution; Australia. Fil: Orrock, John L. University of Wisconsin. Department of Zoology; Estados Unidos Fil: Peri, Pablo Luis. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Santa Cruz; Argentina. Fil: Peri, Pablo Luis. Universidad Nacional de la Patagonia Austral; Argentina. Fil: Peri, Pablo Luis. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Fil: Prober, Suzanne M. Commonwealth Scientific and Industrial Research Organisation Land and Water; Australia. Fil: Risch, Anita C. Swiss Federal Institute for Forest, Snow and Landscape Research. Community Ecology; Suiza Fil: Schütz, Martin. Swiss Federal Institute for Forest, Snow and Landscape Research. Community Ecology; Suiza Fil: Speziale, Karina L. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Investigaciones en Biodiversidad y Medioambiente (INIBIOMA). Universidad Nacional del Comahue; Argentina. Fil: Standish, Rachel J. Murdoch University. School of Veterinary and Life Sciences; Australia. Fil: Sullivan, Lauren L. University of Minnesota. Department of Ecology, Evolution and Behavior; Estados Unidos Fil: Wardle, Glenda M. University of Sydney. School of Biological Sciences; Australia. Fil: Williams, Ryan J. Iowa State University. Agricultural and Biosystems Engineering; Estados Unidos Fil: Yang, Louie H. University of California. Department of Entomology and Nematology; Estados Unidos

Exotic species dominate many communities; however the functional significance of species' biogeographic origin remains highly contentious. This debate is fuelled in part by the lack of globally replicated, systematic data assessing the relationship between species provenance, function and response to perturbations. We examined the abundance of native and exotic plant species at 64 grasslands in 13 countries, and at a subset of the sites we experimentally tested native and exotic species responses to two fundamental drivers of invasion, mineral nutrient supplies and vertebrate herbivory. Exotic species are six times more likely to dominate communities than native species. Furthermore, while experimental nutrient addition increases the cover and richness of exotic species, nutrients decrease native diversity and cover. Native and exotic species also differ in their response to vertebrate consumer exclusion. These results suggest that species origin has functional significance, and that eutrophication will lead to increased exotic dominance in grasslands., It remains unclear whether exotic and native species are functionally different. Using a global grassland experiment, Seabloom et al. show that native and exotic species respond differently to two globally pervasive environmental changes, addition of mineral nutrients and alteration of herbivore density.

Categorizing species according to their functional traits, such as spatial and temporal patterns of resource use, effects on ecosystems, and responses to environmental perturbations, can facilitate successful restoration of plant communities. Functional guilds condense species lists by grouping species according to similarities in characteristics we believe to be important in a particular context. These groupings can allow us to (1) ensure community and ecosystem structural and functional attributes, (2) increase competitiveness of the community to deter the establishment of undesirable species, (3) simplify and test models of community assembly including resistance to invasion, succession, and species coexistence, and (4) facilitate cross-site comparisons. As useful as functional guilds can be, we must not overlook the potentially important roles of individual species. In restoration, including multiple species that represent each functional type within a target community may provide a buffer ag...

National Parks are hallmarks of ecosystem preservation in the United States. The introduction of alien invasive plant species threatens protection of these areas. Bromus tectorum L. (commonly called downy brome or cheatgrass), which is found in Rocky Mountain National Park (hereafter, the Park), Colorado, USA, has been implicated in early spring competition with native grasses, decreased soil nitrogen, altered nutrient and hydrologic regimes, and increased fire intensity. We estimated the potential distribution of B. tectorum in the Park based on occurrence records (n = 211), current and future climate, and distance to roads and trails. An ensemble of six future climate scenarios indicated the habitable area of B. tectorum may increase from approximately 5.5% currently to 20.4% of the Park by the year 2050. Using ordination methods we evaluated the climatic space occupied by B. tectorum in the Park and how this space may shift given future climate change. Modeling climate change at a small extent (1,076 km2) and at a fine spatial resolution (90 m) is a novel approach in species distribution modeling, and may provide inference for microclimates not captured in coarse-scale models. Maps from our models serve as high-resolution hypotheses that can be improved over time by land managers to set priorities for surveys and removal of invasive species such as B. tectorum.

Human alterations to nutrient cycles and herbivore communities are affecting global biodiversity dramatically. Ecological theory predicts these changes should be strongly counteractive: nutrient addition drives plant species loss through intensified competition for light, whereas herbivores prevent competitive exclusion by increasing ground-level light, particularly in productive systems. Here we use experimental data spanning a globally relevant range of conditions to test the hypothesis that herbaceous plant species losses caused by eutrophication may be offset by increased light availability due to herbivory. This experiment, replicated in 40 grasslands on 6 continents, demonstrates that nutrients and herbivores can serve as counteracting forces to control local plant diversity through light limitation, independent of site productivity, soil nitrogen, herbivore type and climate. Nutrient addition consistently reduced local diversity through light limitation, and herbivory rescued diversity at sites where it alleviated light limitation. Thus, species loss from anthropogenic eutrophication can be ameliorated in grasslands where herbivory increases ground-level light. © 2014 Macmillan Publishers Limited. Fil: Borer, Elizabeth. University of Minnesota; Estados Unidos Fil: Seabloom, Eric. University of Minnesota; Estados Unidos Fil: Gruner, Daniel. University of Maryland; Estados Unidos Fil: Harpole, Stanley. Iowa State University; Estados Unidos Fil: Hillebrand, Helmut. Carl-von- Ossietzky University; Alemania Fil: Lind, Eric M.. University of Minnesota; Estados Unidos Fil: Adler, Peter B.. Utah State University; Estados Unidos Fil: Alberti, Juan. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencia Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; Argentina Fil: Anderson, Michael. Wake Forest University; Estados Unidos Fil: Bakker, Jonathan D.. University of Washington; Estados Unidos Fil: Biederman, Lori. Iowa State University; Estados Unidos Fil: Blumenthal, Dana. United States Department of Agriculture. Agricultural Research Service; Estados Unidos Fil: Brown, Cynthia S.. State University of Colorado - Fort Collins; Estados Unidos Fil: Brudvig, Lars A.. University of Minnesota; Estados Unidos Fil: Buckley, Yvonne M.. The University Of Queensland; Australia Fil: Cadotte, Marc. University of Toronto Scarborough; Canadá Fil: Chu, Chengjin. Lanzhou University; China Fil: Cleland, Elsa. University of California; Estados Unidos Fil: Crawley, Michael. Imperial College at Silwood Park; Reino Unido Fil: Daleo, Pedro. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencia Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; Argentina Fil: Damschen, Ellen. University of Wisconsin; Estados Unidos Fil: Davies, Kendi. State University of Colorado - Fort Collins; Estados Unidos Fil: DeCrappeo, Nicole. Forest and Rangeland Ecosystem Science Center; Estados Unidos Fil: Du, Guozhen. Lanzhou University; Estados Unidos Fil: Firn, Jennifer. Queensland University of Technology; Australia Fil: Hautier, Yann. University of Minnesota; Estados Unidos Fil: Heckman, Robert. University of North Carolina at Chapel Hill; Estados Unidos Fil: Hector, Andy. University of Oxford; Reino Unido Fil: Hillerislambers, Janneke. University of Washington; Estados Unidos Fil: Iribarne, Oscar Osvaldo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencia Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; Argentina Fil: Klein, Julia. State University of Colorado - Fort Collins; Estados Unidos Fil: Knops, Johannes M. H.. University of Nebraska; Estados Unidos Fil: La Pierre, Kimberly. University of California; Estados Unidos Fil: Leakey, Andrew D. B.. University of Illinois at Urbana-Champaign; Estados Unidos Fil: Li, Wei. Iowa State University; Estados Unidos Fil: MacDougall, Andrew S.. University of Guelph; Canadá Fil: McCulley, Rebecca. University Of Kentucky; Estados Unidos Fil: Melbourne, Brett. State University of Colorado - Fort Collins; Estados Unidos Fil: Mitchell, Charles. University of North Carolina at Chapel Hill; Estados Unidos Fil: Moore, Joslin. University of Melbourne; Australia Fil: Mortensen, Brent. Iowa State University; Estados Unidos Fil: O'Halloran, Lydia. Oregon State University; Estados Unidos Fil: Orrock, John. University of Wisconsin; Estados Unidos Fil: Pascual, Jesus Maria. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencia Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; Argentina Fil: Prober, Suzanne. CSIRO Ecosystem Sciences; Australia Fil: Pyke, David. Forest and Rangeland Ecosystem Science Center; Canadá Fil: Risch, Anita. Swiss Federal Institute For Forest, Snow And Landscape Research; Suiza Fil: Schuetz, Martin. Swiss Federal Institute For Forest, Snow And Landscape Research; Suiza Fil: Smith, Melinda D.. State University of Colorado - Fort Collins; Estados Unidos Fil: Stevens, Carly. Lancaster University; Reino Unido Fil: Sullivan, Lauren. Iowa State University; Estados Unidos Fil: Williams, Ryan. Iowa State University; Estados Unidos Fil: Wragg, Peter. University of Minnesota; Estados Unidos Fil: Yang, Louie. University of California; Estados Unidos

Invasions have increased the size of regional species pools, but are typically assumed to reduce native diversity. Invasions have increased the size of regional species pools, but are typically assumed to reduce native diversity. However, global-scale tests of this assumption have been elusive because of the focus on exotic species richness, rather than relative abundance. This is problematic because low invader richness can indicate invasion resistance by the native community or, alternatively, dominance by a single exotic species. Here, we used a globally replicated study to quantify relationships between exotic richness and abundance in grass-dominated ecosystems in 13 countries on six continents, ranging from salt marshes to alpine tundra. We tested effects of human land use, native community diversity, herbivore pressure, and nutrient limitation on exotic plant dominance. Despite its widespread use, exotic richness was a poor proxy for exotic dominance at low exotic richness, because sites that contained few exotic species ranged from relatively pristine (low exotic richness and cover) to almost completely exotic-dominated ones (low exotic richness but high exotic cover). Both exotic cover and richness were predicted by native plant diversity (native grass richness) and land use (distance to cultivation). Although climate was important for predicting both exotic cover and richness, climatic factors predicting cover (precipitation variability) differed from those predicting richness (maximum temperature and mean temperature in the wettest quarter). Herbivory and nutrient limitation did not predict exotic richness or cover. Exotic dominance was greatest in areas with low native grass richness at the site- or regional-scale. Although this could reflect native grass displacement, a lack of biotic resistance is a more likely explanation, given that grasses comprise the most aggressive invaders. These findings underscore the need to move beyond richness as a surrogate for the extent of invasion, because this metric confounds monodominance with invasion resistance. Monitoring species' relative abundance will more rapidly advance our understanding of invasions. Fil: Seabloom, Eric W.. University of Minnesota; Estados Unidos Fil: Borer, Elizabeth T.. University of Minnesota; Estados Unidos Fil: Buckley, Yvonne. The University Of Queensland; Australia Fil: Cleland, Elsa E.. University of California, San Diego; Estados Unidos Fil: Kendi, Davies. State University of Colorado Boulder; Estados Unidos Fil: Firn, Jennifer. Queensland University of Technology. Brisbane; Australia Fil: Hartpole, Stanley W.. Iowa State University; Estados Unidos Fil: Hautier, Yann. University of Zurich; Suiza Fil: Lind, Eric. Universidad de Minnesota; Estados Unidos Fil: MacDougall, Andrew. University of Guelph; Canadá Fil: Orrock, John L.. University of Wisconsin; Estados Unidos Fil: Prober, Suzanne M.. CSIRO Ecosystem Sciences; Australia Fil: Adler, Peter. Utah State University; Estados Unidos Fil: Alberti, Juan. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencia Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; Argentina Fil: Anderson, T. Michael. Wake Forest University; Estados Unidos Fil: Bakker, Jonathan D.. University of Washington; Estados Unidos Fil: Biederman, Lori A.. Iowa State University; Estados Unidos Fil: Blumenthal, Dana. Rangeland Resources Research Unit; Estados Unidos Fil: Browns, Cynthia S.. State University of Colorado - Fort Collins; Estados Unidos Fil: Brudvig, Lars A.. Michigan State University; Estados Unidos Fil: Caldeira, Maria. Technical University of Lisbon; Portugal Fil: Chu, Chengjin. Lanzhou University; China Fil: Crawley, Michel. Imperial College London; Reino Unido Fil: Daleo, Pedro. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencia Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; Argentina Fil: Damschen, Ellen I.. University of Wisconsin; Estados Unidos Fil: D'antonio, Carla. University of California; Estados Unidos Fil: Decrappeo, Nicole. Geological Survey Forest and Rangeland Ecosystem Science Center; Estados Unidos Fil: Dickman, Chris. University of Sydney; Australia Fil: Du, Guozhen. Lanzhou University; China Fil: Fay, Philip. Grassland Soil and Water Research Lab; Estados Unidos Fil: Frater, Paul. Iowa State University; Estados Unidos Fil: Gruner, Daniel S.. University of Queensland; Australia Fil: Hagenah, Nicole. University of KwaZulu-Natal; Sudáfrica Fil: Hector, Andrew. University of Zurich; Suiza Fil: Helm, Avellina. University Of Tartu.; Estonia Fil: Hillebrand, Helmut. Carl-von-Ossietzky University; Alemania Fil: Hofmockel, Kirsten. Iowa State University; Estados Unidos Fil: Humphries, Hope. State University of Colorado - Fort Collins; Estados Unidos Fil: Iribarne, Oscar Osvaldo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencia Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; Argentina Fil: Jin, Virginia L.. Agroecosystem Management Research Unit; Estados Unidos Fil: Kay, Adam. University of St. Thomas; Estados Unidos Fil: Kirkman, Kevin. University of KwaZulu-Natal; Estonia Fil: Klein, Julia. State University of Colorado - Fort Collins; Estados Unidos Fil: Knops, Johannes M. H.. University Of Nebraska; Estados Unidos Fil: La Pierre, Kimberly. Yale University; Estados Unidos Fil: Ladwig, Laura M.. University Of New Mexico; Estados Unidos Fil: Lambrinos, John G.. Oregon State University; Estados Unidos Fil: Leakey, Andrew. University of Illinois at Urbana-Champaign; Estados Unidos Fil: Li, Qi. Northwest Institute of Plateau Biology, Chinese Academy of Sciences; China Fil: Li, Wei. Southwest Forestry University; China Fil: McCulley, Rebecca. University Of Kentucky; Estados Unidos Fil: Melbourne, Brett. State University of Colorado Boulder; Estados Unidos Fil: Mitchell, Charles. University of North Carolina; Estados Unidos Fil: Moore, Joslin. Australian Research Centre for Urban Ecology; Australia Fil: Morgan, John. La Trobe University; Australia Fil: Mortensen, Brent. Iowa State University; Estados Unidos Fil: O'Halloran, Lydia. Oregon State University; Estados Unidos Fil: Pärtel, Meelis. University Of Tartu.; Estonia Fil: Pascual, Jesus Maria. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencia Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; Argentina Fil: Pyke, David A.. University of California; Estados Unidos Fil: Risch, Anita. Swiss Federal Institute For Forest, Snow And Landscape Research; Suiza Fil: Salguero Goméz, Roberto. The University Of Queensland; Australia Fil: Sankaran, Mahesh. National Centre for Biological Sciences; India Fil: Schuetz, Martin. Swiss Federal Institute For Forest, Snow And Landscape Research; Suiza Fil: Simonsen, Anna. University of Toronto; Canadá Fil: Smith, Melinda. State University of Colorado - Fort Collins; Estados Unidos Fil: Stevens, Carly. Lancaster Environment Center; Canadá Fil: Sullivan, Lauren. Iowa State University; Estados Unidos Fil: Wardle, Glenda M.. University of Sydney; Australia Fil: Wolkovich, Elizabeth M.. University of British Columbia; Canadá Fil: Wragg, Peter D.. The University Of Queensland; Australia Fil: Wright, Justin. University of Duke; Estados Unidos Fil: Yang, Louie. University of California; Estados Unidos

If one morning I walked on top of the water across the Potomac River, the headline that afternoon would read: "President Can't Swim". —Lyndon B. Johnson Introduction The term “spin” implies manipulating the truth, and this concept, along with “spin doctoring,” is now common in media and public discourse. The prevalence of “spin zones” in American politics is undeniable; media outlets themselves, such as Bill O’Reilly’s “No Spin Zone” on Fox News, now run segments on the topic. Despite this apparent media certainty about what constitutes “spin” there is a lack of conceptual clarity regarding the term among those who study media and politics. This article will draw on previous literature to identify two competing yet overlapping spin zones in American politics: the media’s spin zone and the President’s spin zone. Highlighting examples from the two most recent American presidential election campaigns, the article will evaluate the interplay of these zones and the consequences for future campaigns. Spin Zones In the United States, the press and the President are engaged in a struggle over providing information. Ever since the Watergate Scandal, the media is increasingly expected to be a “watchdog” that informs citizens and keeps the Executive accountable (Coronel 13) The President, conversely, may attempt to use the power of his position to set the discursive agenda or frame the political debate in his favor. Furthermore, with the rise of multi-media access and information provision, the lines between the spin doctoring of the Executive and the media have become even more blurred. Because of the complexities of these overlapping spin zones, many scholars disagree on how to define and/or precisely measure these effects. The following section briefly describes the ‘spin zone’ tools of agenda setting, framing, and priming, and then considers the example of a candidate who failed to prime his negative evaluation and a President who primes his image and successfully counterattacks his negative evaluation. The literature recognises two separate, yet interrelated zones that are integral to understanding these media/presidential relations: what we term the presidential spin zone and the media spin zone. The interplay between these zones comes together around three key concepts—agenda setting, framing, and priming. A key difficulty for scholars is that the President, his electoral challengers, and the press are engaged in agenda setting, framing and priming, sometimes simultaneously. Agenda setting is a broad concept and refers to focusing on certain issues to the exclusion of others. Framing is defined as the decision by the news media to “emphasise certain elements to define the ‘public’s belief’ about social and political issues” (Van Gorp 488). Other scholars describe priming as “a disproportionate amount of public comments with the hope . . . of causing voters to base their selection among the candidates on [that] issue” (Druckman et al. 1181; see also Druckman “Framing Effects”; Nelson, Clawson and Oxley; Van Gorp). Candidates may also undertake “image priming,” which is proposed by James Druckman et al., as a tool that can be used to counteract negative candidate evaluations (1182–1183). The definition of the media spin zone is, in most instances, synonymous with priming. Defining the presidential spin zone is more complex. Clearly the presidential spin zone involves both the previously-discussed “issue framing abilities of the president” and how he “set[s] the agenda” (Miller and Krosnick 301; see also, Gamson and Modigliano, Baumgardner and Jones; Druckman, “Framing Effects”). Mark Rozell, for instance, found that the Ford and Carter administrations had difficulty controlling the public agenda since many issues were either beyond their control, or because the president and his advisors lacked the strategy or skill to affect media coverage. The Reagan White House however was able to use his “image” to control the media (85–86). Similarly, George W. Bush’s administration was able to implement policies concerning the invasion of Iraq after the 9-11 through “issue framing” scare tactics, which were constantly reinforced by media outlets (Kellner 643). However, the President can also be engaged in priming at any given time. In other words, the President (or candidate) may attempt to prime what the media has already spun about him/her. A problem, of course, is that the President or candidate, in attempting to prime an issue that has already been spun in a sense tacitly admits they have lost the opportunity to set the agenda in the first place. However, this is when he can seize the aforementioned opportunity to use “image priming” to counterattack the media. In the examples that follow we examine whether the President or candidate can use priming to effectively counterattack the media spin zone, with a focus on two political tools that have been historically reserved for the President or candidates, namely, holding the base and wedge issues. Holding the Base and the Media Spin Zone Holding the base has been defined as a way in which candidates or Presidents can use the media to strengthen support among voters who already identify with their political party (Iyengar and McGrady 246). A classic example of this is the 1984 Reagan/Bush re-election campaign, the “The Bear.” This featured a bear in the woods that “some” could “see” and others didn’t “see at all” which was an implicit threat regarding Soviet communism and a reminder that Reagan was tough on foreign policy (“The Bear”). However, the evidence indicates that the media has increasingly begun “holding the base” on its own to facilitate its partisan framing and priming of candidates or Presidents. The Swift Boat Veterans for Truth attack advertisements on 2004 Democratic presidential candidate John Kerry is a key example of a media attempt to “hold the base.” In these advertisements, former “Swift Boat Veterans attack[ed] his [Kerry’s] military record” (Muravchik A17). While this initiative began as a means to collect Republican donations, Shanto Iyengar and Jennifer McGrady maintain that the amount was “trivial” and that the real impact came with “the torrent of news reports across the country” (150). Indeed, Kathleen Jamieson and Joseph Capella found that by August 2004, “viewers of Fox News were more likely than other network viewers to say that candidate John Kerry did not earn his Vietnam medals” (279). Their evaluation of this data demonstrated the power of the media spin zone: “He (Limbaugh) employs intense language, disparaging information and negative framing to distance perceptions of the Democratic candidate from those of the anointed Republican candidate” (Jamieson and Capella 228). The coverage of disputes surrounding Kerry’s military record was augmented by the media’s simultaneous coverage of the threat of terrorism. This priming “in the media continued, reaching a high peak of 55 threat messages in August 2004, a month later 25% of the public was very concerned about another major terrorist attack in the US—two months before the presidential election” (Nacos, Bloch-Elkon and Shapiro 120). Both President Bush and Candidate Kerry acknowledged that their respective win/loss could be attributed in some measure to the press coverage of the “war on terror” (Nacos, Bloch-Elkon and Shapiro 124). While questions loomed about his military experience against the backdrop of the war on terror, Senator Kerry won the first two Presidential debates by significant margins. Alec Gallup and Frank Newport suggested that the Kerry camp had “won the spin contest … to characterize their own candidate as the winner” (406). So, what happened to Kerry? The media spin zone stopped him. The presidential debate wins were 30 September 2004 and 8 October 2004, respectively. Iyengar and McGrady demonstrate that before the debates even began the number of Swift Boat veteran stories primed in the national and international press went from under 100 to over 500 (151). According to Kim Fridkin et al. the media’s spin was a significant factor in the third debate. They found that media coverage concerning Senator Kerry’s response to one question on whether homosexuality was a choice affected citizens’ evaluations of the candidate. In the post debate coverage, the tone “in newspapers, on the Internet, and on television was uniformly negative in its assessment of Senator Kerry’s comments” (Fridkin et al. 30). The impact of this negative framing was sufficiently strong to override positive evaluations of Kerry held by those who watched the debate. In sum, the “perfect storm of media coverage lessened the bounce that Senator Kerry received from the actual debate and led people to develop negative impressions of Kerry a mere three weeks before Election Day” (Fridkin 43). Despite these liabilities, Kerry should have counterattacked the media spin zone. He should have “counterpunched,” as noted by Drew Westen, priming the media that he was “a different kind of Democrat”—“one who knows when it’s time to take off the gloves” (337). Westen’s advice is echoed in Druckman’s call for further research in this area as well as by his own research findings. The media’s framing and priming led to negative evaluations of Kerry, which afforded him the opportunity to prime his “image” in a counterattack, as Druckman suggests (1183). Overcoming the Wedge Issues of the Media Spin Zone President Obama, however, orchestrates a different outcome in dealing with the media spin zone attack against him which centered on a “wedge” or “us verses them” issue. Iyengar and McGrady note that “wedge issues are designed to pit groups against each other, to appeal to voters’ sense of group identity” (145). However, they define wedge issues within the context of presidential spin zones; thus, the candidate or the president would be framing the “us versus them” topic. In this instance, the media framed a wedge issue, the status of President Obama’s citizenship, against him. In this case the birther movement, oft-promoted by conservative radio host Rush Limbaugh, argued that President Obama was not a US citizen. This issue became so prominent that it was soon adopted by the media spin zone. The media framing demanded proof in addition to the short form birth certificate that the President had already released (Wilson 109). For his part, President Obama handled the media spin zone’s wedge issue with great aplomb, responding in a brief statement to the public on 27 April 2011: “We do not have time for this kind of silliness” (Shear). Moreover, he did not alienate the media for framing the birther movement, but he placed the blame implicitly on Donald Trump who had taken up the birther gauntlet thrown down by Rush Limbaugh. It was “clearly Trump” he was priming when he indicated that he did not want to be “distracted by sideshows and carnival barkers” (Shear). Moreover, his strategic focus on “silliness” is an illustration of “image priming”. He did not allow himself to be drawn into the race-baiting or religious controversy that was a component of some of the media talk show discussions. The Washington Post reported after Obama’s speech that the percentage of Americans who questioned his legitimacy to serve as President dropped from 20% to 10%—thus legitimating his choice to address the nation. This result meant that the President responded to an attack from the media spin zone with a counterattack of his own; he effectively counterattacked to prime his image. Interestingly, Stephen Ansolobehare and Iyengar have indirectly demonstrated the efficacy of counterattacks in presidential spin zone situations by evaluating situations where one candidate attacks another and the “victim” of the attack either, does not respond, responds with a positive message or responds with a counterattack (143). They found overwhelming evidence that voters prefer their party’s candidate to counterattack rather than be victimised. Conclusion In this paper we have furthered the call for conceptual clarity in the field by joining Druckman et al. in emphasising the need for more research on “image priming” on the part of candidates and Presidents in the interplay between the press and the presidency. If used properly, image priming seems a viable way for the presidency to counterattack against media framing and priming, but squandered opportunities may irreparably harm candidates. President Obama faced a difficult wedge issue that had undercurrents of both racial and religious tensions, but he deftly avoided those issues and found a way to “use Trump as a foil and present the president as a more serious leader” (Shear). His counterattack against the wedge used by the media spin zone was successful. Senator Kerry, on the other hand, failed to counterattack the media spin zone’s rallying of the base. His silence allowed the media to generate both issue and image frames and priming against him. This is an important lesson for future candidates and presidents and the media and presidential spin zones are important topics for further research. References Ansolabehare, Stephen, and Shanto Iyengar. Going Negative: How Political Advertisements Shrink and Polarize the Electorate. New York: Free Press, 1995. Baumgardner, Frank, and Bryan D. Jones. Agendas and Instability in American Politics. Chicago, Illinois: U of Chicago P, 1993. Cappella, Joseph N., and Kathleen Hall Jamieson. Spiral of Cynicism: The Press and the Public Good. New York: Oxford UP, 1997. Coronel, Sheila S. “The Media as Watchdog.” The Role of the News Media in the Governance Realm 29–31 May 2008. 18 Oct. 2011 ‹http://www.hks.harvard.edu/fs/pnorris/Conference/Conference%20papers/Coronel%20Watchdog.pdf›. Druckman, James N. “On the Limits of Framing Effects: Who Can Frame?” The Journal of Politics 63.4 (2001): 1041–1066. ——. “The Power of Television Images.” The Journal of Politics 65.2 (2003): 559–71. Druckman, James N., et al. “Candidate Strategies to Prime Issues and Image.” The Journal of Politics 66.4 (2004): 1180–1202. Esser, Frank, Carsten Reinemann, and David Fan. “Spin Doctoring in British and German Election Campaigns: How the Press Is Being Confronted with a New Quality of Political PR.” European Journal of Communication 15.2 (2000): 209–239. Fridkin, Kim L., et al. “Spinning Debates: The Impact of the News Media’s Coverage of the Final 2004 Presidential Debate.” The International Journal of Press/Politics 13.1 (2008): 29–51. Funk, Carolyn. “Bringing the Candidate in Models of Candidate Evaluation.” The Journal of Politics 61.3 (1999): 700–720. Gallup, Alec M., and Frank Newport. The Gallup Poll: Public Opinion in 2004. Lanham, Maryland: Rowland & Littlefield Publishers, 2006 Gamson, William A., and Andre Modigliani. “Media Discourse and Public Opinion on Nuclear Power: A Constructionist Approach.” American Journal of Sociology 95.1 (1989): 1–37. Goffman, Erving. Frame Analysis: An Essay on the Organization of Experience. New York: Harper and Row, 1974 Iyengar, Shanto, and Jennifer A. McGrady. Media Politics: A Citizens Guide. New York: W.W. Norton, 2007. Iyengar, Shanto, and Donald R. Kinder. News That Matters. Chicago: U of Chicago P, 1987. Jacobs, Lawrence R., and Robert Y. Shapiro. “Politicians Don’t Pander: Political Manipulation and the Loss of Democratic Responsiveness.” Chicago: U of Chicago P, 2000. Jamieson, Kathleen Hall, and Joseph N. Capella. Echo Chamber: Rush Limbaugh and the Conservative Media Establishment. New York: Oxford UP, 2008. Kellner, Douglas. “Bushspeak and the Politics of Lying: Presidential Rhetoric in the War on Terror.” Presidential Studies Quarterly 37.4 (2007): 622–645. Miller, Joanne M., and Jon A. Krosnick. “News Media Impact on the Ingredients of Presidential Evaluations: Politically Knowledgeable Citizens are Guided by a Trusted Source.” American Journal of Political Science 44.2 (2000): 301-315. Muravchik, Joshua. “Kerry’s Cambodia Whopper.” Washington Post 24 Aug. 2004: A17. Nacos, Brigette L., Yaeli Boch-Elkon, Robert Y. Shapiro. “Post 9-11 Terrorism Threats, News Coverage, and Public Perceptions in the United States.” International Journal of Conflict and Violence 1.2 (2007): 105–126. Nelson, Thomas E., Rosalee A. Clawson, and Zoe M. Oxley. “Media Framing of Civil Liberties Conflict and Its Effect on Tolerance.” American Political Science Review 91 (1997): 567-583. Rozell, M.J. “Presidential Image-Makers on the Limits of Spin Control.” Presidential Studies Quarterly 25.1 (1995): 67–90. Scheufele, Dietram A., and David Tewksbury. “Framing, Agenda Setting, and Priming: The Evolution of Three Media Effects Models.” Journal of Communication 57.1 (2007): 9–20. Shear, Michael D. “With Document, Obama Seeks to End Birther Issue.” New York Times 28 April 2011. 18 Oct 2011 ‹http://www.nytimes.com/2011/04/28/us/politics/28obama.html›.“The Bear.” 4President TV 2 Oct 1984. 18 Oct 2011 ‹http://tv.4president.us/1984/reagan1984bear.htm›. Tversky, Amos, and Daniel Kahneman. “The Framing of Decisions and the Psychology of Choice.” Science 211.4481 (1981): 452–58. Van Gorp, Baldwin. “Where Is the Frame: Victims and Intruders in the Belgian Press Coverage of the Asylum Issue?” European Journal of Communication 20.4 (2005): 484–507. Westen, Drew. The Political Brain. New York: Public Affairs, 2007. Wilson, John K. The Most Dangerous Man in America: Rush Limbaugh’s Assault on Reason. New York: St. Martin’s Press, 2011.

For more than 30 years, the relationship between net primary productivity and species richness has generated intense debate in ecology about the processes regulating local diversity. The original view, which is still widely accepted, holds that the relationship is hump-shaped, with richness first rising and then declining with increasing productivity. Although recent meta-analyses questioned the generality of hump-shaped patterns, these syntheses have been criticized for failing to account for methodological differences among studies. We addressed such concerns by conducting standardized sampling in 48 herbaceous-dominated plant communities on five continents. We found no clear relationship between productivity and fine-scale (meters(-2)) richness within sites, within regions, or across the globe. Ecologists should focus on fresh, mechanistic approaches to understanding the multivariate links between productivity and richness.

Many ecosystems worldwide are dominated by introduced plant species, leading to loss of biodiversity and ecosystem function. A common but rarely tested assumption is that these plants are more abundant in introduced vs. native communities, because ecological or evolutionary-based shifts in populations underlie invasion success. Here, data for 26 herbaceous species at 39 sites, within eight countries, revealed that species abundances were similar at native (home) and introduced (away) sites - grass species were generally abundant home and away, while forbs were low in abundance, but more abundant at home. Sites with six or more of these species had similar community abundance hierarchies, suggesting that suites of introduced species are assembling similarly on different continents. Overall, we found that substantial changes to populations are not necessarily a pre-condition for invasion success and that increases in species abundance are unusual. Instead, abundance at home predicts abundance away, a potentially useful additional criterion for biosecurity programmes.

High-impact biological invasions often involve establishment and spread in disturbed, high-resource patches followed by establishment and spread in biotically or abiotically stressful areas. Evolutionary change may be required for the second phase of invasion (establishment and spread in stressful areas) to occur. When species have low genetic diversity and short selection history, within-generation phenotypic plasticity is often cited as the mechanism through which spread across multiple habitat types can occur. We show that trans-generational plasticity (TGP) can result in pre-adapted progeny that exhibit traits associated with increased fitness both in high-resource patches and in stressful conditions. In the invasive sedge, Cyperus esculentus, maternal plants growing in nutrient-poor patches can place disproportional number of propagules into nutrient-rich patches. Using the invasive annual grass, Aegilops triuncialis, we show that maternal response to soil conditions can confer greater stress tolerance in seedlings in the form of greater photosynthetic efficiency. We also show TGP for a phenological shift in a low resource environment that results in greater stress tolerance in progeny. These lines of evidence suggest that the maternal environment can have profound effects on offspring success and that TGP may play a significant role in some plant invasions.

In recent decades, a growing number of studies have addressed connections between ecological and evolutionary concepts in biologic invasions. These connections may be crucial for understanding the processes underlying invaders’ success. However, the extent to which scientists have worked on the integration of the ecology and evolution of invasive plants is poorly documented, as few attempts have been made to evaluate these efforts in invasion biology research. Such analysis can facilitate recognize well-documented relationships and identify gaps in our knowledge. In this study, we used a network-based method for visualizing the connections between major aspects of ecology and evolution in the primary research literature. Using the family Poaceae as an example, we show that ecological concepts were more studied and better interconnected than were evolutionary concepts. Several possible connections were not documented at all, representing knowledge gaps between ecology and evolution of invaders. Among knowledge gaps, the concepts of plasticity, gene flow, epigenetics and human influence were particularly under-connected. We discuss five possible research avenues to better understand the relationships between ecology and evolution in the success of Poaceae, and of alien plants in general.

Low-ranked coals were dissolved by using cell extracts derived from liquid cultures of Trametes versicolor . The coal-solubilizing agent (CSA) was separated from the broth components by a multistep isolation procedure including reverse-phase high-pressure liquid chromatography, size exclusion chromatography, ethanol fractionation, and recrystallization. Staircase voltammetry was used to show that two CSA moieties can coordinate to aqueous copper(II) ion. A molecular weight determination (using amperometry) gave an apparent molecular weight of 1.3 4 × 10 2 g/mol ± 8%. Nuclear magnetic resonance indicated that all protons on CSA are exchangeable in D 2 O and that there is only one type of carbon in CSA. The infrared spectrum of recrystallized CSA is identical to that of ammonium oxalate, and X-ray studies confirmed the crystal structure and composition of CSA to be that of ammonium oxalate monohydrate. The equivalent weight of the coal in solution, when the coal was dissolved by ammonium oxalate, is 7,940 g of coal per mol of iron present in the coal.

Fire is a natural part of most forest ecosystems in the western United States, but its effects on nonnative plant invasion have only recently been studied. Also, forest managers are engaging in fuel reduction projects to lessen fire severity, often without considering potential negative ecological consequences such as nonnative plant species introductions. Increased availability of light, nutrients, and bare ground have all been associated with high- severity fires and fuel treatments and are known to aid in the establishment of nonnative plant species. We use vegetation and environmental data collected after wildfires at seven sites in coniferous forests in the western United States to study responses of nonnative plants to wildfire. We compared burned vs. unburned plots and plots treated with mechanical thinning and/or prescribed burning vs. untreated plots for nonnative plant species richness and cover and used correlation analyses to infer the effect of abiotic site conditions on invasibility. Wildfire was responsible for significant increases in nonnative species richness and cover, and a significant decrease in native cover. Mechanical thinning and prescribed fire fuel treatments were associated with significant changes in plant species composition at some sites. Treatment effects across sites were minimal and inconclusive due to significant site and site 3 treatment interaction effects caused by variation between sites including differences in treatment and fire severities and initial conditions (e.g., nonnative species sources). We used canonical correspondence analysis (CCA) to determine what combinations of environmental variables best explained patterns of nonnative plant species richness and cover. Variables related to fire severity, soil nutrients, and elevation explained most of the variation in species composition. Nonnative species were generally associated with sites with higher fire severity, elevation, percentage of bare ground, and lower soil nutrient levels and lower canopy cover. Early assessments of postfire stand conditions can guide rapid responses to nonnative plant invasions.

A species-addition experiment showed that prairie grasslands have a structured, nonneutral assembly process in which resident species inhibit, via resource consumption, the establishment and growth of species with similar resource use patterns and in which the success of invaders decreases as diversity increases. In our experiment, species in each of four functional guilds were introduced, as seed, into 147 prairie–grassland plots that previously had been established and maintained to have different compositions and diversities. Established species most strongly inhibited introduced species from their own functional guild. Introduced species attained lower abundances when functionally similar species were abundant and when established species left lower levels of resources unconsumed, which occurred at lower species richness. Residents of the C4 grass functional guild, the dominant guild in nearby native grasslands, reduced the major limiting resource, soil nitrate, to the lowest levels in midsummer and exhibited the greatest inhibitory effect on introduced species. This simple mechanism of greater competitive inhibition of invaders that are similar to established abundant species could, in theory, explain many of the patterns observed in plant communities.

Accurate and reliable predictions of invasive species distributions are urgently needed by land managers for developing management plans and monitoring new potential areas of establishment. Presence-only species distribution models are commonly used in these evaluations, however they are rarely tested with independent data over time or compared with presence-absence models fit with the same presence data. Using Maxent, we developed a presence-only model of invasive cheatgrass (Bromus tectorum L.) distribution in Rocky Mountain National Park, Colorado, USA in 2007 fit with limited data, and then tested the model with independent presence and absence data collected between 2008 and 2013. This model was verified using threshold dependent and threshold independent evaluation metrics. Next, we developed a Maxent model with cheatgrass presence data from 2007 through 2013 (i.e. Maxent 2013), and compared this model to a presence-absence method (i.e., generalized linear model; GLM 2013) using the same data. Threshold dependent and threshold independent evaluation metrics suggested Maxent 2013 outperformed GLM 2013, and a two-tailed Wilcoxon signed rank test indicated relative probability outputs were not significantly different between the models in geographic space. Based on known presences and absences of cheatgrass collected in the field, the Maxent 2013 and GLM 2013 relative probability outputs were highly correlated at absence locations but less correlated at presence locations. A Kappa comparison of Maxent 2007 and Maxent 2013 binary output provides evidence that Maxent is robust when fit with limited data. Our results indicate Maxent is an appropriate model for use when land management objectives are supported by limited resources and thus require a conservative, but highly accurate estimate of habitat suitability for invasive species on the landscape.