[Colloquium] Talk by Stefano Allesina, NCEAS on April 17, 2008

[Katie Casey]

DEPARTMENT OF COMPUTER SCIENCE

UNIVERSITY OF CHICAGO

Date: Thursday, April 17, 2008
Time: 2:30 p.m.
Place: KPTC 120

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Speaker:	Stefano Allesina

From:		NCEAS

Web page:	www.nceas.ucsb.edu/~allesina

Title: Stability in Ecological Networks: Large Effects of Small Motifs

Abstract: Large number of species interact and coexist in the  
intricate networks of consumer–resource interactions known as food  
webs. For decades ecologists held the view that more complex  
ecosystems, those with a larger number of species and connections,  
were also more likely to be persistent, explaining therefore the  
extremely high biodiversity we observe in nature. Robert May's  
mathematical argument on stability, however, proved that large,  
complex networks of ecological interactions with random structure tend  
invariably to instability. This result ignited the "complexity- 
stability" debate that has been one of the main drivers of theoretical  
ecology for three decades. Here we revisit May's argument and show  
that, when species interact as predators and prey, systems as complex  
as the ones observed in nature can still be stable. Moreover,  
stability is highly robust to perturbations of interaction strength,  
and is largely a property of structure driven by predator–prey loops.  
The results highlight the role of small modules for the persistence of  
large networks, so that the stability of small motifs can cascade in  
that of the whole network.
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Host:	Nina Hinrichs
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