- Anusha Uppaluri 1

Contents  Problem  Problems Importance  Research Methodology  Data Collection  Conclusion  References  Questions 2 2

Problem  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 3

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 4 4

Research Methodology  Main question: Eliminating what nodes in the food web network would cause the maximum shattering of the networks stability 5

 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 6

Step I  Elimination of nodes can also be done on a random basis  Nodes are removed randomly  Network reaction is judged based on robustness  The species that cause the steepest plunge in robustness can be focused 7

 Random node removal though not of much help might help with new ideas and give the simulation a new direction 8

Step II  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 9

 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 10

Step III  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 11

 The answers obtained from the above III steps are analyzed to reach a final conclusion  Any further experimentation is done if needed 12

Data Collection  Food web data sets 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 13

 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 14

Conclusion  Collect data from recent literature and recent data source  Reconstruct the network using Pajek  Follow a III step process  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 15

 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 16

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 , 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 , 2002  Gilbert A.J., “ Connectance indicates the robustness to food webs when subjected to species loss”, Ecological Indicators, Vol. 9, pp ,

Questions? 18