Natural Security: A Darwinian Approach to a Dangerous World

14. Network Analysis Links Parts to the Whole

Chapter 14 NETWORK ANALYSIS LINKS PARTS TO THE WHOLE FERENC JORDÁN 240 The Importance of Being Linked We live in an increasingly globalized and interconnected world. As the conventional wisdom states, everything is connected to everything else, including humans, ecosystems, and nations. Physicists have examined this complexity , first as a research curiosity, later as a field of science, and currently as a new conceptual paradigm. In this chapter, I present some interesting and notable similarities between ecological and social networks and outline how our knowledge in one field may help in better understanding the other. In particular, I focus on how ecological network theory might help us in thinking about homeland security and understanding modern terrorism in a globalized and interconnected world. One tool for studying complex systems is network analysis, mostly done in cooperation between physicists, biologists, and scientists belonging to any discipline, having recognized the significance of network studies. Network science is reviving (Strogatz 2001) but not new (e.g., Harary 1959). The main message is even older: we have to study the whole in order to better understand the parts, and vice versa. This is the essence of holistic thinking . What is new is that the traditionally soft, subjective, and occasionally rather mystic statements and approaches of holistic scientists are becoming harder, quantitative, and more scientific. Thanks mostly to network theory and the capacity of computers, now we can calculate to what extent elements are connected to other elements within a network, we can measure complexity and the quantitative relationship between the parts and the whole. Network theory can be applied to different fields (also in interaction with systems theory and cybernetics), either for better understanding the natural systems surrounding us, or for designing better technological systems. Recently, network analysis has been proposed widely as a new tool for exposing and visualizing otherwise probably hidden patterns in political sciences (Johnson and Krempel 2004; Keefe 2006; but see also a skeptical critique: Farley 2006). Our network-related knowledge may provide a robust background for defense and homeland security in the future. Being linked within a network offers both possibilities and constraints. An example from ecology is that the fate of populations of different species depends on their interactions. Specialist predators (like species A in Fig. 14.1a) may go extinct as prey (species E in Fig. 14.1a) go extinct. If a predator feeds on several prey species (species A in Fig. 14.1b), the extinction of one of the prey (e.g., species D in Fig. 14.1b) will not cause its extinction, since it can switch to relying more on alternative resources (species E and F in Fig. 14.1b). A higher number of feeding interactions may increase the resilience of the predator against loosing one of the prey species. However, it can also NETWORK ANALYSIS 241 A E A D E F A C E A B C D E F A B C D F A B C D E F (b) (c) (d) (e) (f) (a) figure 14.1 Six small graphs presenting typical parts of food webs, where nodes and links represent species and their ecological interactions , respectively. Species A is a specialist consumer in some cases (a) but a generalist in others (b). c. An indirect interaction, called “trophic cascade” is shown, where A eats C eating E, and the outcome is a positive effect from A to E. d. A “wasp-waist” food web architecture with several species at low and high trophic levels but only one in the middle (C). e. A loop can be seen containing B, C, and F. f. A food web completed by thick nontrophic interactions (for example, E can be algae living on the surface of the fish A). All these cases are discussed in the text. 242 SYNTHESIS happen that a particular species goes extinct because of its interactions: kelp forests may disappear if the sea urchin population grows, following the local extinction of sea otters (Estes et al. 1998). Sea otters, feeding on kelp-consuming sea urchins, drive a trophic cascade effect helping the survival of the kelp forest. If the first species dies, the third one may follow it because of their indirect network connection (see Fig. 14.1c, where sea otter is A, sea urchin is C, and kelp forest is E). This situation is familiar in conventional wisdom: the enemies of our enemies tend...