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Events on Tuesday, April 11th, 2017

Chaos & Complex Systems Seminar
The influence of spatial connectivity on landscape regime shifts and pattern formation after external pulses
Time: 12:05 am
Place: 4274 Chamberlin (refreshments will be served)
Speaker: Zak Ratajczak, UW Department of Zoology
Abstract: Ecosystems are often exposed to driver pulses, such as climate oscillations or consumer outbreaks. We currently lack robust theoretical predictions for when a driver pulse will elicit regime shifts, which are instances when an ecosystem no longer recovers to its essential form, functions, and feedbacks. We used a spatially extended vegetation model where increases in grazing pressure can force patches of the landscape to undergo a regime shift from a high productivity state to a self-reinforcing low-productivity state. We considered a factorial combination of driver pulses that increase grazing pressure by differing intensities and for differing durations. These pulses were applied to simulated landscapes with high underlying spatial heterogeneity and differing levels of spatial connectivity between adjacent patches. We considered two scales of resistance to regime shifts: landscape integrity, defined as when >95% of the landscape returned to a high biomass state and refugia potential, defined as the ability to keep >5% of the landscape in the high biomass state. High connectivity landscapes had greater landscape integrity, meaning that they could withstand more intense and longer pulses, and still have a majority of the landscape return to a high biomass state. Low connectivity systems, in contrast, had greater refugia potential, meaning that at least a small portion of the landscape was able to return to a high biomass state, even after more intense or longer pulses. Systems with intermediate connectivity had a more balanced combination of landscape integrity and refugia potential. These landscapes also tended to form coherent spatial patterns after driver pulses that nearly forced a landscape-scale regime shift. Such pattern formation could potentially be used as a warning sign for adaptive management. Ensemble, these simulations suggest that underlying landscape characteristics can greatly alter the landscape and patch-scale potential for regime shifts in response to various external pulses.
Host: Clint Sprott
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Council Meeting
Council Meeting
Time: 12:00 pm
Place: 2314 Chamberlin hall
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"Physics Today" Undergrad Colloquium (Physics 301)
Superconductivity
Time: 1:20 pm
Place: 2241 Chamberlin Hall
Speaker: Robert J Joynt, UW Madison Department of Physics
Host: Wesley Smith
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Theory Seminar (High Energy/Cosmology)
Dark Matter Interpretations of the AMS Positron Excess
Time: 3:30 pm
Place: 5280 Chamberlin
Speaker: Ian Low, Northwestern
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