Flies as bioindicators of grazing pressures in Mongolia

2016 ◽  
Author(s):  
Rebecca A Clement
Keyword(s):  
Grazing Pressures

scholarly journals A dinoflagellate exploits toxins to immobilize prey prior to ingestion

2010 ◽  
Vol 107 (5) ◽  
pp. 2082-2087 ◽  
Author(s):  
Jian Sheng ◽  
Edwin Malkiel ◽  
Joseph Katz ◽  
Jason E. Adolf ◽  
Allen R. Place
Keyword(s):  
High Speed ◽  
Algal Bloom ◽  
Harmful Algal Bloom ◽  
Fish Kills ◽  
Karlodinium Veneficum ◽  
Prey Behavior ◽  
Dense Suspensions ◽  
Holographic Microscopy ◽  
Critical Understanding ◽  
Grazing Pressures

Toxins produced by the harmful algal bloom (HAB) forming, mixotrophic dinoflagellate Karlodinium veneficum have long been associated with fish kills. To date, the perceived ecological role for toxins has been relief from grazing pressures. Here, we demonstrate that karlotoxins also serve as a predation instrument. Using high-speed holographic microscopy, we measure the swimming behavior of several toxic and nontoxic strains of K. veneficum and their prey, Storeatula major, within dense suspensions. The selected strains produce toxins with varying potency and dosages, including a nontoxic one. Results clearly show that mixing the prey with the predatory, toxic strains causes prey immobilization at rates that are consistent with the karlotoxins’ potency and dosage. Even prey cells that continue swimming slow down after exposure to toxic predators. The swimming characteristics of predators vary substantially in pure suspensions, as quantified by their velocity, radii of helical trajectories, and direction of helical rotation. When mixed with prey, all toxic strains that are involved in predation slow down. Furthermore, they substantially reduced their predominantly vertical migration, presumably to remain in the vicinity of their prey. Conversely, the nontoxic control strain does not alter its swimming and does not affect prey behavior. In separate experiments, we show that exposing prey to exogenous toxins also causes prey immobilization at rates consistent with potency. Clearly, the toxic predatory strains use karlotoxins as a means of stunning their prey, before ingesting it. These findings add a substantiated critical understanding for why some HAB species produce such complex toxin molecules.

Grazing Pressures and Animal Performance from Pearl Millet 1

1977 ◽  
Vol 69 (6) ◽  
pp. 983-987 ◽  
Author(s):  
M. M. McCartor ◽  
F. M. Rouquette
Keyword(s):  
Pearl Millet ◽  
Animal Performance ◽  
Grazing Pressures

Examining the genetic diversity of Stipa grandis under various grazing pressures

2006 ◽  
Vol 26 (10) ◽  
pp. 3175-3182 ◽  
Author(s):  
Dan Shan ◽  
Mengli Zhao ◽  
Bing Han ◽  
Guodong Han
Keyword(s):  
Genetic Diversity ◽  
Grazing Pressures

scholarly journals Stocker performance and production in mixed tall fescue–bermudagrass pastures of the Southern Piedmont USA

2012 ◽  
Vol 28 (2) ◽  
pp. 160-172 ◽  
Author(s):  
Alan J. Franzluebbers ◽  
John A. Stuedemann ◽  
Dwight H. Seman
Keyword(s):  
Tall Fescue ◽  
Cynodon Dactylon ◽  
Stocking Density ◽  
Warm Season ◽  
Grazing Pressure ◽  
Pasture Management ◽  
Coastal Bermudagrass ◽  
Forage Utilization ◽  
Environmental Goals ◽  
Grazing Pressures

AbstractStocker performance and production from mixed cool- and warm-season perennial pastures are important determinants of agricultural sustainability that can be influenced by management. We evaluated the factorial combination of three sources of nutrient application (inorganic only, organic+inorganic combination, and organic only) and two forage utilization regimes [low grazing pressure (LGP) and high grazing pressure (HGP)] on steer stocking density and rate, performance and production during 7 years of pasture management {tall fescue [Lolium arundinaceum (Schreb.) Darbysh.] overseeded into existing Coastal bermudagrass [Cynodon dactylon (L.) Pers.] sod} on a Typic Kanhapludult in Georgia, USA. Nutrient source had few major impacts on responses, except for lower animal performance with organic fertilization (broiler litter) than with organic+inorganic and inorganic only fertilization, especially with LGP. Seasonal changes in stocking weight and rate occurred, not only as expected due to environmental conditions and dominant forage species present, but that also counteracted expected differences imposed by grazing pressure; signaling negative feedback of HGP on forage productivity. Steer performance was greatest in spring and summer under both grazing pressures, but was significantly reduced with increasing grazing pressure in the autumn and winter due to low forage availability. Across years, steer gainha−1 (863kgha−1) was not different between grazing pressures, but gainha−1 declined with time under HGP and was stable with time under LGP. Reducing grazing pressure to a moderate level can lead to equivalent steer production as HGP, and would likely contribute to a more sustainable balance among production, socio-economic and environmental goals. These multi-year results will help cattle producers in warm, moist climates design and implement more sustainable grazing systems.

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