Download Food Webs

- Anusha Uppaluri
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Contents
Problem
Problems Importance
Research Methodology
Data Collection
Conclusion
References
Questions
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Problem
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Food Webs – Complex networks formed by one
species of animals feeding on the other species
Target Groups – Species of animals which
when extinct cause the near extinction/
extinction of a large number of species of
animals
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Problems Importance
Food webs make a very complex network and its
understanding would be interesting
Interdependence of species in food web is
important to maintain balance
Helps in understanding the do’s and don'ts in
trying to preserve our environment and
ecosystem
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Research Methodology

Main question: Eliminating what nodes in the
food web network would cause the maximum
shattering of the networks stability
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Collect data from recent related literature and
recreate network
Pajek can be used for network creation and
analysis
Nodes in the network are eliminated according
to a certain criteria
Reaction of the remaining network is judged
Robustness of the remaining network is
calculated
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Step I
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Elimination of nodes can also be done on a
random basis
Nodes are removed randomly
Network reaction
robustness
is
judged
based
on
The species that cause the steepest plunge in
robustness can be focused
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
Random node removal though not of much help
might help with new ideas and give the
simulation a new direction
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Step II
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Nodes can be eliminated on the basis of their
indegree centraility
Indegree centrality of all the nodes is calculated
The nodes with the highest indegree centrality
are eliminated first and so on
After each elimination the robustness of the
remaining network is calculated
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The species that causes the steepest plunge in
robustness upon its elimination is zeroed in on
Intuition behind using indegree centrality: if a
species is being fed on by many other animals
then it is an important part of the network
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Step III
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Nodes can be eliminated on the basis of their
betweeness centraility aswell
Previously mentioned process is eliminated
while considering betweeness centrality
The intution behind using betweeness centrality
is, is a node is on several shortest paths
between pairs several other nodes => it is
important to maintain the balance in the system
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The answers obtained from the above III steps
are analyzed to reach a final conclusion
Any further experimentation is done if needed
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Data Collection
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Food web data sets
The problem is the above data sets are too
small
Working with them would give an initial idea of
what the network reacts like and what the
answers could be
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Focus on recent sources of data and recent
related literature
Older sources of data were found to be weak
and incomplete
Main data to be obtained from the literature
studied
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Conclusion

Collect data from recent literature and recent
data source
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Reconstruct the network using Pajek
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Follow a III step process

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Eliminate nodes on a random basis and analyze
the reaction of the network
Eliminate the nodes on indegree centrality basis
and analyze the reaction of network
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
Eliminate the nodes on the basis of
betweenness centrality and analyze the
reaction of the network
Use the results found in the above III step
process to either reach the conclusion or to
perform any further experimentation as needed
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References
Dunne J. A., Williams R. J., Martinez N. D., “ Food-web structure
and network theory: The role of connectance and size”,
Proceedings of National Academy of Sciences of United States of
America, Vol. 99 No. 20, pp. 12917-12922, 2002
Dunne J. A., Williams R. J., Martinez N. D., “ Network structure
and biodiversity loss in food webs: robustness increases with
connectance”, Ecology Letters, Vol. 5, pp. 558-567, 2002
Gilbert A.J., “ Connectance indicates the robustness to food
webs when subjected to species loss”, Ecological Indicators, Vol.
9, pp. 72-80, 2009
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Questions?
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