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Systems ecology (Rev #6, changes)

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Contents

Idea

Systems ecology is an interdisciplinary field of ecology, taking a holistic approach to the study of ecological systems, especially entire ecosystems. Systems ecology can be seen as an application of general systems theory to ecology. Central to the systems ecology approach is the idea that an ecosystem is a complex system exhibiting emergent properties. Systems ecology focuses on interactions and transactions within and between biological and ecological systems, and is especially concerned with the way the functioning of ecosystems can be influenced by human interventions. It uses and extends concepts from thermodynamics and develops other macroscopic descriptions of complex systems.

Examples

Howard Odum

The ‘Energy Systems Language’ was developed by Howard T. Odum and his colleagues in the 1950s during studies of the tropical forests funded by the United States Atomic Energy Commission. Odum is the founder of ‘systems ecology’:

Sometimes called ‘Energese’, the Energy Systems Language is a diagrammatic language featuring elements like these:

Energy Systems Symbols

His most detailed book on diagrams for systems ecology seems to be this:

  • Howard T. Odum, Systems Ecology: an Introduction, Wiley-Interscience, New York, 1983.

In this book:

  • R. L. Kitching, Systems Ecology: An Introduction to Ecological Modelling, University of Queensland Press, 1983.

the author writes:

Because of its electrical analogy, the Odum system is relatively easy to turn into mathematical equations…. If one is building a model of energy flow then certainly the Odum system should be given serious consideration…

According to the Wikipedia article on Odum, the Energy Systems Language language looks similar to the Systems Modeling Language recently developed by INCOSE, an international Systems Engineering body.

Climate change impact on forests

Dr. Andreas Fischlin is a Systems Ecology scientist who has contributed to IPCC reports. His work is mainly in modelling ecosystems, in collaboration with field researchers. He focuses on the impact of climate change on ecosystems, especially forest.

There are many types of model. A commonly used type involves ‘patch dynamics’. For example, an old tree dies, leaving a gap, and seedlings compete for light and nutrients. Seedlings vary: some tolerate shadows, others need more light, and so on. The model tracks individual trees and includes environmental variables such as precipitation which shape the competition. Such models are caricatures or cartoons, and do not attempt to match reality, but can nonetheless capture crucial aspects of a real forest. Different models suit different purposes: one would be used for predicting climate change impact, another for deciding how to best fertilise a forest.

These are some of the best models in ecology. They can predict what kind of natural forest you will find at a particular location, given information about the climate and soil. As well as predicting what we find today, they can also match what happened at the end of the last ice age, as determined from pollen data. This gives some confidence that they can predict what kind of forests we will have in the future.

Food webs

An interesting question in systems ecology is: which factors make a food web stable or unstable? For decades there has been an intense debate on this question, beginning with quite crude models and moving to ever more realistic ones, and also featuring ever more careful experiments. An excellent review article, featuring a large bibliography, is:

  • Louis-Félix Bersier, A history of the study of ecological networks, in Biological Networks, ed. Francois Képès, World Scientific, Singapore, 2007.

Here is a moe recent article on in the this subject: line of work:

Phillip P. A. Staniczenko, Owen T. Lewis, Nick S. Jones and Felix Reed-Tsochas, Structural dynamics and robustness of food webs, Ecology Letters

  • Phillip P. A. Staniczenko, Owen T. Lewis, Nick S. Jones and Felix Reed-Tsochas, Structural dynamics and robustness of food webs, Ecology Letters 13 (2010), 891-899.

Abstract:: Food web structure plays an important role when determining robustness to cascading secondary extinctions. However, existing food web models do not take into account likely changes in trophic interactions (‘rewiring’) following species loss. We investigated structural dynamics in 12 empirically documented food webs by simulating primary species loss using three realistic removal criteria, and measured robustness in terms of subsequent secondary extinctions. In our model, novel trophic interactions can be established between predators and food items not previously consumed following the loss of competing predator species. By considering the increase in robustness conferred through rewiring, we identify a new category of species–overlap species–which promote robustness as shown by comparing simulations incorporating structural dynamics to those with static topologies. The fraction of overlap species in a food web is highly correlated with this increase in robustness; whereas species richness and connectance are uncorrelated with increased robustness. Our findings underline the importance of compensatory mechanisms that may buffer ecosystems against environmental change, and highlight the likely role of particular species that are expected to facilitate this buffering.

Felix Reed-Tsochas is the head of the Complex Agent-Based Dynamic Networks (or ‘CABDyn’) group at the University of Oxford:

References

Here is a good place to start:

Odum’s book:

  • Howard T. Odum, Systems Ecology: an Introduction, Wiley-Interscience, New York, 1983.

is a classic reference. The account of Fischlin’s work is based on this interview. Our section on Odum is taken from

  • John Baez and Jacob Biamonte, Diagrams.