Understanding Food Web Robustness: The Impact of Connectance and Degree Distribution, Slides of Data Communication Systems and Computer Networks

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Target Groups in Food Webs

Contents

• Problem
• Problems Importance
• Related Work
• Conclusion
• References
• Questions

A Very Simple Food Web

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

• Food webs with low or high connectance aren't usually found
• Understanding of food web degree distribution and connectance helps estimating its reaction towards structural changes

Dunne et. al.

• 16 food webs were considered
• Primary species loss was simulated
• Robustness of food webs in terms of secondary extinctions is measured
• Food webs are more robust in case of random species removal than in case of removal of species with many links to other species
• Posses thresholds beyond which food webs are quiet sensitive to highly connected species removal

Alison J. Gilbert

• Changes in connectance cause changes in robustness?
• If poorly connected species are lost => connectance increases. Does this => increase in robustness?
• Does converse hold good?
• Robustness – likelihood to lose nodes secondarily
• Fragility - converse of robustness
• Connectance – degree to which nodes of a system are connected to each other

• Loss of poorly connected species – positive change in connectance
• Loss of highly connected species – negative change in connectance
• Intercept – number of connections of the species at which change in connectance becomes positive from negative
• Intercept is always and integer and loss in species will lead to change in connectance

• Steep decline in connectance are more likely to cause secondary species loss
• Huge negative changes to connectance => large negative impact on robustness
• Increase in connectance from removal of least connected nodes => lesser secondary losses but still reduces robustness
• Loss of any species causes reduction in robustness irrespective of their connections
• Connectance changes little with random species removal

• Loss of species => change in connectance => loss of robustness
• Connection between robustness , small negative and huge positive changes to connectance cannot be ascertained
• Highly robust food webs => smaller changes to connectance with species loss
• In food webs with uniform degree distribution, species loss do not cause large changes to connectance

Conclusion

• High connectance – uniform degree distribution
• Middle connectance – exponential distribution
• Low connectance - power law or partial power law
• Food webs are more robust in case of random species removal than in case of removal of species with many links to other species
• Food webs with high connectance display high sensitivity from the beginning
• Loss of any species causes reduction in Docsity.com^16

• Huge negative changes to connectance => large negative impact on robustness
• Increase in connectance from removal of least connected nodes => lesser secondary losses but still reduces robustness
• Robustness doesn’t just depend on connectance
• Robustness is related to degree distribution