Plant traits and functional types in response to reduced disturbance in a semi‐natural grassland

Abstract. Question: How do functional types respond to contrasting levels of herbage use in temperate and fertile grasslands? Location: Central France (3°1’E, 45°43’N), 870 m a.s.l. Methods: Community structure and the traits of dominant plant species were evaluated after 12 years of contrasted grazing and mowing regimes in a grazing trial, comparing three levels of herbage use (high, medium and low). Results and Conclusions: Of 22 measured traits (including leaf traits, shoot morphology and composition, phenology), seven were significantly affected by the herbage use treatment. A decline in herbage use reduced individual leaf mass, specific leaf area and shoot digestibility, but increased leaf C and dry matter contents. Plants were taller, produced larger seeds and flowered later under low than high herbage use. Nine plant functional response types were identified by multivariate optimization analysis; they were based on four optimal traits: leaf dry matter content, individual leaf area, mature plant height and time of flowering. In the high‐use plots, two short and early flowering types were co‐dominant, one competitive, grazing‐tolerant and moderately grazing‐avoiding, and one grazing‐avoiding but not ‐tolerant. Low‐use plots were dominated by one type, neither hardly grazing‐avoiding nor grazing‐tolerant, but strongly competitive for light.     

Are removal experiments effective tools for assessing plant community resistance and recovery from invasion?

Removal experiments are useful tools for assessing two important aspects of plant community invasion: (1) resistance to invasion and (2) recovery after invasive species removal. We discuss the potential of such experiments based on a brief systematic review of the literature on community resistance, as measured by invasibility after removal of resident species (reduction of taxonomic/functional richness), and on community recovery, as measured by resident community response after invasive species removal. We found 62 research articles, most of them related to invasive species removal. Few studies used removals to test biotic resistance, despite the importance of resident removals for identifying community components that play key roles in the often‐controversial invasion resistance hypotheses. Furthermore, appropriate experimental controls were rarely used, which would allow separation of the effect of local species extinction from that of disturbance. We hope this review stimulates plant ecologists to adopt removal experiments for studying invasion processes.     

Woody species patterns at forest–grassland boundaries in southern Brazil

Vegetation mosaics of grassland/savanna and forest can be found in tropical and subtropical regions of the world, as in southern Brazil, where climate conditions are suitable for forest. Changes in intensity or frequency of disturbances could enable woody species encroachment in grassland communities; however, the processes are related to site conditions and life history of pioneer species. In this paper, we study transition patterns of forest to grassland in the absence of grazing, but under different site conditions related to aspect (landscape position) and time since the last burn. Data are based on shrub and tree species composition and soil variables at forest–grassland boundaries. We found 119 woody species of 42 families along transects of 27 m into the forest and 31.5 m into the grassland. Gradients from forest to grassland were analysed as compositional trajectories in ordination space and differences in the spatial patterns depicted between distinct site aspects. The time since the last fire did not influence these patterns. Inside the forest, tree species diversity was significantly higher close to the edge, independent of the density of individuals. Two main mechanisms may promote forest expansion into the grassland. First, a gradual tree encroachment near the edge and, second, a mechanism linked to the recruitment of isolated pioneer trees within the grassland matrix, most frequently near rocky outcrops, where a decrease in grass biomass leads to low-intensity fires. Despite vegetation patterns at boundaries differing according to aspect, the most important explanatory factor was the distance from the forest border, not just by itself, but with all correlated parameters that are changing along the gradient.     

Tricyclic GyrB/ParE (TriBE) Inhibitors: A New Class of Broad-Spectrum Dual-Targeting Antibacterial Agents

Increasing resistance to every major class of antibiotics and a dearth of novel classes of antibacterial agents in development pipelines has created a dwindling reservoir of treatment options for serious bacterial infections. The bacterial type IIA topoisomerases, DNA gyrase and topoisomerase IV, are validated antibacterial drug targets with multiple prospective drug binding sites, including the catalytic site targeted by the fluoroquinolone antibiotics. However, growing resistance to fluoroquinolones, frequently mediated by mutations in the drug-binding site, is increasingly limiting the utility of this antibiotic class, prompting the search for other inhibitor classes that target different sites on the topoisomerase complexes. The highly conserved ATP-binding subunits of DNA gyrase (GyrB) and topoisomerase IV (ParE) have long been recognized as excellent candidates for the development of dual-targeting antibacterial agents with broad-spectrum potential. However, to date, no natural product or small molecule inhibitors targeting these sites have succeeded in the clinic, and no inhibitors of these enzymes have yet been reported with broad-spectrum antibacterial activity encompassing the majority of Gram-negative pathogens. Using structure-based drug design (SBDD), we have created a novel dual-targeting pyrimidoindole inhibitor series with exquisite potency against GyrB and ParE enzymes from a broad range of clinically important pathogens. Inhibitors from this series demonstrate potent, broad-spectrum antibacterial activity against Gram-positive and Gram-negative pathogens of clinical importance, including fluoroquinolone resistant and multidrug resistant strains. Lead compounds have been discovered with clinical potential; they are well tolerated in animals, and efficacious in Gram-negative infection models.     

Population response to environmental productivity throughout the annual cycle in a migratory songbird

Environmental factors affect migratory animal populations in every phase of their annual cycle and have significant impacts on breeding success and survival. The Breeding Bird Survey provides a long-term database for examining population trends in North American birds, allowing us to examine large-scale environmental factors that influence population abundance. We examined plant productivity as measured by normalized difference vegetation index (NDVI) over a 24-year period from 1983–2006 in bird conservation regions (BCRs) that overlapped Bullock's oriole (Icterus bullockii) breeding, moult, and wintering ranges to ask whether plant productivity in 1 year influences population abundance in the subsequent breeding season. Bullock's orioles have a moult-migration strategy, with a stopover moult in the Mexican monsoon region, which necessitates examining each stationary phase of the bird's annual cycle to understand the impacts of environmental factors on population abundance. Our results show increased breeding abundance in three (Great Basin, Coastal California and Shortgrass Prairies) of the six BCRs in which the species breeds following years with high NDVI values. We did not detect a response of breeding abundance to high NDVI values in the previous year in either the moulting region or in their primary over-wintering area in central Mexico. Our results demonstrate that large-scale annual variation in primary productivity on the breeding grounds can have an impact on breeding abundance in the following season, but further studies on migratory connectivity and on ecological mechanisms during the non-breeding seasons are needed to understand why we did not detect an influence of productivity during these periods.