In a 0.2 ha flight pen, groups of 4 American coots were tested to determine if their grazing activity could be affected by application of a registered granular-trimethacarb insecticide. In the 3 days following treatment (3 kg/ha, a.i.), grazing activity in the treated portions of the 200 m experimental plots was reduced an average of 47X. Overall use of the treated areas followed a similar patt...

1. Grazing and fire are disturbances integral to the evolution and maintenance of savanna grasslands. Humans are altering or completely eliminating these disturbance regimes at a global scale, with important consequences for savanna ecosystem structure and function. It is unknown whether the alteration of these disturbance regimes will have similar effects on grass communities of savanna grassl...

This study considers the stability of two stratified immiscible incompressible fluids in a horizontal channel of infinite extent. Of particular interest is the case with the heavier fluid initially lying above the lighter fluid, so that the system is susceptible to the classical Rayleigh-Taylor instability. An electric field acting in the horizontal direction is imposed on the system and it is ...

We classify in this article the structure and its transitions/évolution of the Taylor vortices with perturbations in one of the following catégories: a) the Hamiltonian vector fields, b) the divergencefree vector fields, and c). the solutions of the Navier-Stokes équations on the two-dimensional torus. This is part of a project orient ed toward to developing a geometrie theory of incompressible...

The possibility of trading greenhouse gas emission permits as a result of the Kyoto Protocol has spurred interest in developing land-based sinks for greenhouse gases. Extensive grazing lands that have the potential to develop substantial woody biomass are one obvious candidate for such activities. However, such activities need to consider the possible impacts on existing grazing and the possibl...

Predicting where state-changing thresholds lie can be inherently complex in ecosystems characterized by nonlinear dynamics. Unpacking the mechanisms underlying these transitions can help considerably reduce this unpredictability. We used empirical observations, field and laboratory experiments, and mathematical models to examine how differences in nutrient regimes mediate the capacity of macrop...

Among the thousands of unicellular phytoplankton species described in the sea, some frequently occurring and bloom-forming marine dinoflagellates are known to produce the potent neurotoxins causing paralytic shellfish poisoning. The natural function of these toxins is not clear, although they have been hypothesized to act as a chemical defence towards grazers. Here, we show that waterborne cues...

n 1939, the Taylor Instrument CompaI nies introduced a completely redesigned version of its “Fulscope” pneumatic controller: this new instrument provided, in addition to proportional and reset control actions, an action which the Taylor Instrument Companies called “pre-act.” In the same year the Foxboro Instrument Company added “Hyper-reset’’ to the proportional and reset control actions provid...

Cover crops are a suite of non-marketable plant species grown to improve soil quality. They may have additional benefits including reduced weed pressure and enhanced habitat for beneficial arthropods, but they do not provide direct revenue. Integrating sheep grazing for cover crop termination could make the use of cover crops more economically feasible. However, if grazing shifts biological com...

rayleigh-taylor (rt) instability has a growing importance in many fields including aircraft industry and astrophysics. the development and the growth of rt instability were investigated using sinusoidal disturbances with different wavelength at the interface of two fluids. numerical simulations were performed by solving navier-stokes unsteady equations with the vof formulation. results of the 2...