Indirect effects and informational entropy in natural and human networks

Systems ecology attempts to study ecological systems in a holistic fashion. Its branch called network ecology in particular deals with ecological systems, notably food webs, as networks of nodes – species or functional groups – that interact with each other by means of predation. Methods of network analysis quantifying effects of both direct and indirect interactions (i.e., those involving intermediate nodes) were first suggested by systems ecologists [1]. These methods were based on analyses of the matrix of stationary systems flows and were applied to food webs to reveal ecological relationships among system components.

ASA is developing applications of network analysis to study food webs. In 2014 researchers [2] investigated the impact of the construction of a dam on the upper Mekong River on the river’s food web; they found the most valued fishery to be significantly impacted and potentially endangered because of the dam construction. Network-based methodology assessing the potential environmental impact of multiple stressors after damming (i.e., sedimentation, discharge change, and heavy metal pollution) provides a new way of highlighting which factors are dominant for the ecosystem and how the management strategies should be prioritized.

Inspired by the power of network ecology methodology ASA is exploring its potential to be transferred to various other applications. Results published in 2014 include: application of the network ecology paradigm to study embodied water consumption by [3]; and a case study of application of network ecology to explore the symbiosis of the plant system in Shandong Lubei eco-industrial park in China by analyzing the sulfur flows that occur in production [4].

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Using network ecology to study the functioning of the city also appears to be promising [5]. Starting from the input-output data and monetary flows between the city’s economic sectors, ASA researchers are studying urban energy metabolism by means of the network-based analysis. In [6][7][8] the time dynamics of embodied energy consumption and associated carbon footprints were investigated, as well as the ecological role of economic sectors in Beijing; this revealed the ecological hierarchy of the urban metabolic system. In [9] the transfer routes of major air pollutant, total suspended particulate matter (TSPM), were studied between the urban ecosystem and surrounding regions in the Beijing–Tianjin–Hebei area. The study identified major TSPM sources by analyzing the embodied TSPM flows through inter-regional trade. Tracking TSPM from origin to end via consumption activities provided a new approach and insights into developing air pollution mitigation strategies.

Another approach to studying networked human-made systems developed by ASA is based on the notion of informational entropy. It is known that physical systems consisting of large number of elements (especially statistically simple systems such as gases) are subject to the maximum entropy principle. In [10] the authors introduced a so-called generalized entropy and showed that the maximum (generalized) entropy principle also holds for more complex systems, whose elements interact strongly and have memory and path-dependence, thus suggesting a powerful theoretical tool for studying such systems.

Last edited: 12 March 2015