Posted by
Dan Kunkle on
URL: http://friam.383.s1.nabble.com/Diversity-and-Stability-in-Food-Webs-tp520801p520803.html
Here's a talk at Northeastern tomorrow that relates to this topic,
with a CS focus instead of a biological one. I thought I would pass it
along, more to highlight the work itself than to have people attend
(which I'm sure would be very difficult for most FRIAMers). The
speaker's web page is:
http://www.ccs.neu.edu/home/riccardo/-Dan
------
TITLE: A SEMANTIC FRAMEWORK FOR DIVERSITY
WHO: Professor Riccardo Pucella
WHEN: Thursday (November 10th), 3:00 PM, 366 WVH
ABSTRACT
Computers that execute the same program risk being vulnerable to the
same attacks. This explains why the Internet, whose machines
typically have much software in common, is so susceptible to viruses,
worms, and other forms of malware. It is also a reason that
replication of servers does not necessarily enhance the availability
of a service subject to attack.
Diversity is an obvious defense. A set of replicas is diverse in so
far as all implement the same functionality but differ in their
implementation details. Diverse replicas are less prone to having
vulnerabilities in common, because attacks typically depend on memory
layout and/or instruction sequence specifics. But building multiple
distinct versions of a program is expensive, so researchers have
turned to mechanical means for creating diverse replicas via
transformations: relocation and/or padding the run-time stack by
random amounts, re-arranging basic blocks and code within basic
blocks, and randomly changing the names of system calls or instruction
opcodes.
Different classes of transformations are more or less effective in
defending against different classes of attacks. Although knowing this
correspondence is important when designing a set of defenses for a
given threat model, knowing the correspondences is not the same as
knowing the overall power of mechanically-generated diversity as a
defense. In this talk, I explore that latter, broader, issue,
investigating two complementary points:
(1) a formal characterization of what attacks cannot be blunted by
mechanically-generated diversity, and
(2) a rigorous comparison of mechanically-generated diversity to
type systems, another commonly advocated defense.
This is joint work with Fred Schneider (Cornell University).
On 11/9/05, Jochen Fromm <fromm at vs.uni-kassel.de> wrote:
>
> Does increasing diversity affect the stability in
> ecosystems and food-webs? If so, is the effect positive
> or negative, i.e. does increasing diversity lead to
> stability or fragility of the system ? Common sense
> says that systems with low diversity (for instance artificial
> monocultures) have low stability and are vulnerable
> to parasites, infections and diseases.
>
> Yet does declining diversity ultimately lead to reductions
> in food-chain length and ecosystem stability ? The relation
> between diversity, food-chain length and ecological processes
> seens to be complex. Ecosystems do not contain only linear
> food-chains, they consist of complex recurrent food-webs.
> If I remember it correctly, even in simple Lotka-Volterra
> equations with more than 2 dimensions chaotic structures can
> arise (in 2 dimensions with 2 species there is the usual
> predator-prey limit cycle, but in 3 dimensions there are
> also strange attractors possible. I have read it somewhere,
> but I can't remember where).
>
> Insights in this ongoing diversity-stability debate
> could be useful, because consumer-producer or
> predator-prey relations can be found in many complex
> systems. The SFI has an interesting site with
> many links about it at
http://discuss.santafe.edu/paleofoodwebs/> for example the following:
>
> (a)
> The diversity-stability debate
> Kevin Shear McCann, Nature 405 (2000) 228-233
>
http://discuss.santafe.edu/files/paleofoodwebs/McCann2000Nature.pdf>
> (b)
> The long and short of food-chain length
> David M. Post, Trends in Ecology & Evolution Vol.17 No.6 June (2002) 269-277
>
http://discuss.santafe.edu/files/paleofoodwebs/Post2002TREE.pdf>
> (c)
> Stability in Real Food Webs: Weak Links in Long Loops
> Anje-Margriet Neutel et al., Science 296 (2002) 1120-1123
>
http://discuss.santafe.edu/files/paleofoodwebs/Neuteletal2002Science.pdf>
> (a) is a nice review, (b) argues that the food-chain length is
> influenced by many factors, ecosystem size and age, degree of
> ecological isolation, natural resource availability, and
> predator-prey interactions, and (c) says that "trophic loops",
> i.e. closed food-chains, add stability to the system, esp.
> the particularly long ones which contain many weak links.
> They found that "loop weights" of the longer loops were low
> in real systems.
>
> -J.
>
>
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