3,118 research outputs found
Effects of Catastrophic Seagrass Loss and Predation Risk on the Ecological Structure and Resilience of a Model Seagrass Ecosystem
As climate change continues, climactic extremes are predicted to become more frequent and intense, in some cases resulting in dramatic changes to ecosystems. The effects of climate change on ecosystems will be mediated, in part, by biotic interactions in those ecosystems. However, there is still considerable uncertainty about where and how such biotic interactions will be important in the context of ecosystem disturbance and climactic extremes.
Here, I review the role of consumers in seagrass ecosystems and investigate the ecological impacts of an extreme climactic event (marine heat wave) and subsequent widespread seagrass die-off in Shark Bay, Western Australia. Specifically, I compare seagrass cover, shark catch rates, and encounter rates of air breathing fauna in multiple habitat types before and after the seagrass die-off to describe post-disturbance dynamics of the seagrass community, shifts in consumer abundances, and changes in risk-sensitive habitat use patterns by a variety of mesoconsumers at risk of predation from tiger sharks (Galeocerdo cuvier). Finally, I conducted a 16 month field experiment to assess whether xi loss of top predators, and predicted shifts in dugong foraging, could destabilize remaining seagrass.
I found that the previously dominant temperate seagrass Amphibolis antarctica is stable, but not increasing. Conversely, an early-successional tropical seagrass, Halodule uninervis, is expanding. Following the die-off, the densities of several consumer species (cormorants, green turtles, sea snakes, and dugongs) declined, while others (Indo-Pacific bottlenose dolphins, loggerhead sea turtles, tiger sharks) remained stable. Stable tiger shark abundances following the seagrass die-off suggest that the seascape of fear remains intact in this system. However, several consumers (dolphins, cormorants) began to use dangerous but profitable seagrass banks more often following seagrass decline, suggesting a relaxation of anti-predator behavior. Experimental results suggest that a loss of tiger sharks would result in a behaviorally mediated trophic cascade (BMTC) in degraded seagrass beds, further destabilizing them and potentially resulting in a phase shift. My work shows that climactic extremes can have strong but variable impacts on ecosystems mediated in part by species identity, and that maintenance of top predator populations may by important to ecological resilience in the face of climate change
Evidence for Charging Effects in CdTe/CdMgTe Quantum Point Contacts
Here we report on fabrication and low temperature magnetotransport
measurements of quantum point contacts patterned from a novel two-dimensional
electron system - CdTe/CdMgTe modulation doped heterostructure. From the
temperature and bias dependence we ascribe the reported data to evidence for a
weakly bound state which is naturally formed inside a CdTe quantum
constrictions due to charging effects. We argue that the spontaneous
introduction of an open dot is responsible for the replacement of flat
conductance plateaus by quasi-periodic resonances with amplitude less than
2e^{2}/h, as found in our system. Additionally, below 1 K a pattern of weaker
conductance peaks, superimposed upon wider resonances, is also observed.Comment: 4 pages, 4 figure
Dynamical ultrafast all-optical switching of planar GaAs/AlAs photonic microcavities
The authors study the ultrafast switching-on and -off of planar GaAs/AlAs
microcavities. Up to 0.8% refractive index changes are achieved by optically
exciting free carriers at 1720 nm and a pulse energy of 1.8 micro Joules. The
cavity resonance is dynamically tracked by measuring reflectivity versus time
delay with tunable laser pulses, and is found to shift by as much as 3.3
linewidths within a few picoseconds. The switching-off occurs with a decay time
of around 50 ps. The authors derive the dynamic behavior of the carrier density
and of the complex refractive index. They propose that the inferred 10 GHz
switching rate may be tenfold improved by optimized sample growth.Comment: 1.) Replaced figure 1 (linear reflectivity) with a more recent and
improved measurement 2.) Included a Figure of Merit for switching and
compared to other recent contributions 3.) Explained more precisely the
effect of embedded Quantum Dots (namely no effect on measurement) 4.) Changed
wording in a few place
Generic polynomial vector fields are not integrable
AbstractWe study some generic aspects of polynomial vector fields or polynomial derivations with respect to their integration. In particular, using a well-suited presentation of Darboux polynomials at some Darboux point as power series in local Darboux coordinates, it is possible to show, by algebraic means only, that the Jouanolou derivation in four variables has no polynomial first integral for any integer value s ≥ 2 of the parameter.Using direct sums of derivations together with our previous results we show that, for all n ≥ 3 and s ≥ 2, the absence of polynomial first integrals, or even of Darboux polynomials, is generic for homogeneous polynomial vector fields of degree s in n variables
Complex bounds for multimodal maps: bounded combinatorics
We proved the so called complex bounds for multimodal, infinitely
renormalizable analytic maps with bounded combinatorics: deep renormalizations
have polynomial-like extensions with definite modulus. The complex bounds is
the first step to extend the renormalization theory of unimodal maps to
multimodal maps.Comment: 20 pages, 3 figure
Greenland Ice Sheet Surface Melt and Its Relation to Daily Atmospheric Conditions
Melt area is one of the most reliably monitored variables associated with surface conditions over the full Greenland Ice Sheet (GrIS). Surface melt is also an important indicator of surface mass balance and has potential relevance to the ice sheet's global sea level contribution. Melt events are known to be spatially heterogeneous and have varying time scales. To understand the forcing mechanisms, it is necessary to examine the relation between the existing conditions and melt area on the time scales that melt is observed. Here, we conduct a regression analysis of atmospheric reanalysis variables including sea level pressure, near-surface winds, and components of the surface energy budget with surface melt. The regression analysis finds spatial heterogeneity in the associated atmospheric circulation conditions. For basins in the southern GrIS, there is an association between melt area and high pressure located south of the Denmark Strait, which allows for southerly flow over the western half of the GrIS. Instantaneous surface melt over northern basins is also associated with low pressure over the central Arctic. Basins associated with persistent summer melt in the southern and western GrIS are associated with the presence of an enhanced cloud cover, a resulting decreased downwelling solar radiative flux, and an enhanced downwelling longwave radiative flux. This contrasts with basins to the north and east, where an increased downwelling solar radiative flux plays a more important role in the onset of a melt event. The analysis emphasizes the importance of daily variability in synoptic conditions and their preferred association with melt events
Painful skin eruption in a professional auto mechanic — a quiz
-A 37-year-old man, auto mechanic by trade, presented with multiple facial skin lesions, accompanied by burning sensation and pain, eye redness, fever and fatigue. The symptoms occurred 4 days before admission. Two weeks earlier he was consulted dermatologically due to hand eczema treated subsequently with topical steroids; additionally, he reported presence of concomitant facial erythema with scaling. Besides, the personal and familial medical history was unremarkable. Clinical examination revealed multiple skin erosions covered with serosanguineous crust, disseminated on his face, hands and forearms (Fig. 1); increased body temperature of 38.7 degrees Celsius, and conjunctival congestion. Laboratory tests revealed increased level of inflammatory parameters (C-reactive protein 21.25 mg/L, leukocytosis 13.48 ×109/L)
Quantum Deformations of Space-Time Symmetries with Mass-Like Deformation Parameter
The difficulties with the measurability of classical space-time distances are
considered. We outline the framework of quantum deformations of D=4 space-time
symmetries with dimensionfull deformation parameter, and present some recent
results.Comment: 4 pages, LaTeX, uses file stwol.sty, to be published in the
Proceedings of XXXII International Rochester Conference in High Energy
Physics (Warsaw, 24.07-31.07 1996
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