Emergent Phenomena

Complex systems produce surprising behavior; in fact, they produce behavioral patterns and properties that just cannot be predicted from knowledge of their parts taken in isolation. These so-called 'emergent properties' are probably the single most distinguishing feature of

Environmental change

Task switching

Environmental change

Increase in food availability

Midden worker

Patrolling ant

Task switching

Forager

Nest maintenance worker

Increase in food availability

Forager

Forager

Brood-care worker, nest construction, seed storage, reserves

Detritus on surface of nest mound

Brood-care worker, nest construction, seed storage, reserves

Nest maintenance worker

Detritus on surface of nest mound

Nest maintenance worker

Patrolling ant

Intrusion by foreign ants Figure 2 Task switching in a harvester ant colony.

Table 1 The main surprise-generating mechanisms

Mechanism

Surprise effect

Paradoxes Inconsistent phenomena

Instability Large effects from small changes

Incomputability Behavior transcends rules

Connectivity Behavior cannot be decomposed into parts

Emergence Self-organizing patterns complex systems. An example of this phenomenon occurs when one considers a collection of independent random quantities, such as the heights of all the people in New York City. Even though the individual numbers in this set are highly variable, the distribution of this set of numbers will form the familiar bell-shaped curve of elementary statistics. This characteristic bell-shaped structure can be thought of as 'emerging' from the interaction of the component elements. Not a single one of the individual heights can correspond to the normal probability distribution, since such a distribution implies a population. Yet when they are all put into interaction by adding and forming their average, the 'central limit theorem' of probability theory tells us that this average and the dispersion around it must obey the bell-shaped distribution.

Ecological Complexity

Complexity research has discovered that many systems display common structural and behavioral/dynamical characteristics (Table 2). The interplay of these complex system characteristics entails systems to exhibit properties such as surprise, emergence, and power law scaling. Ecological complexity is the observation that ecological systems exhibit many of the same properties as physical complex systems, and thus an active research program has arisen over the analysis of ecological data to see to what extent ecosystems share these common properties with other complex systems.

Ecosystems are composed of a large number of highly diverse components interacting with self-stabilizing and

Table 2 Some characteristics of complex systems

Structural characteristics

Large number of components

Large number of components

High diversity of components and connections

Asymmetries

Strong interactions

Hierarchic organization self-promoting feedback to produce emergent patterns. As such, ecological systems have been described as complex, adaptive, hierarchical systems (CAHS) or self-organized, hierarchical open (SOHO) systems. Unlike with complex physical systems, openness is a property that is required of all ecological systems. This is because ecological systems are self-perpetuating through means of capturing energy, doing useful work (biochemical reactions, growth, and maintenance) to persist at least momentarily at a highly organized state far from thermodynamic equilibrium - this is the metabolic process. A second ecological-defining feature is that organisms are able to replicate themselves such that the system outlives the constituent parts - this is the reproductive process. Therefore, it is often said of an ecosystem that, 'the whole is more than the sum of the parts'.

Two of the most pressing issues regarding ecological complexity are the need to develop appropriate measures to quantify the structural and behavioral complexity of ecosystems, and to identify the underlying processes that generate this complexity, through theory, analysis, modeling, and field studies.

A new journal, Ecological Complexity (Elsevier), is one forum for this research since 2004. The journal considers papers dealing with biocomplexity related to the environment with an emphasis on interdisciplinary and integrated natural and social systems science. Topics typically found in the journal include:

• all aspects of biocomplexity in the environment and theoretical ecology;

• ecosystems and biospheres as complex adaptive systems;

• self-organization of spatially extended ecosystems;

• emergent properties and structures of complex ecosystems;

• ecological pattern formation in space and time;

• the role of biophysical constraints and evolutionary attractors on species assemblages;

• ecological scaling (scale invariance, scale covariance, and across-scale dynamics), allometry, and hierarchy theory;

• ecological topology and networks;

• studies toward an ecology of complex systems;

• complex systems approaches for the study of dynamic human-environment interactions;

Behavioral/dynamical characteristics

Nonlinear

Chaotic

Catastrophic

Self-organization

Multiple steady states

Adaptive

• using knowledge of nonlinear phenomena to better guide policy development for adaptation strategies and mitigation to environmental change; and

• new tools and methods for studying ecological complexity.

The emphasis on integrated natural and social systems addresses the growing interest to understand the role of human influence on the environment. There is a recent awareness ofthe need to alter this influence in some fashion both for ourselves and our environment. New tools and approaches incorporating self-organization, emergence, and co-adaptation are needed to improve our ability to manage and restore natural systems. These new approaches to ecosystem management must also account for the natural dynamics and integrate concepts of sustainable development. Advances in ecological complexity science are essential in successfully navigating this transition.

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