Patch dynamics

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[edit] Definitions

Patch dynamics is a conceptual approach to ecosystem and habitat analysis that emphasizes dynamics of heterogeneity within a system. Diverse patches of habitat created by natural disturbance regimes are seen as critical to maintenance of diversity.

A habitat patch is defined as any discrete area that is used by a species for breeding or for obtaining other resources. [1] They have a definite shape and spatial configuration, or heterogeneity.

Mosaics are defined as the patterns within landscapes that are composed of smaller elements, such as individual forest stands, shrubland patches, highways, farms, or towns.

[edit] Patches and Mosaics

Historically, due to the short time scale of human observation, mosaic landscapes were perceived to be static. This focus centered around the idea that the status of a particular population, community, or ecosystem could be understood by studying a particular patch within a mosaic. However, this perception ignored the conditions that interact with and connect patches. In 1979, Bormann and Likens coined the phrase "shifting mosaic" to describe the theory that landscapes change and fluctuate and are in fact dynamic. This is related to the battle of cells that occurs in a Petri dish.

Patch dynamics refers to this concept that all landscapes are in fact dynamic. There are three states that a patch can found in: potential, active, and degraded. Patches in the potential state are transformed into active patches through colonization of the patch by dispersing species arriving from other active or degrading patches. Patches are transformed from the active state to the degraded state when the patch is abandoned, and patches change from degraded to potential through a process of recovery. [2] Logging, fire, farming, and reforestation all contribute to the process of colonization, and can effectively change the shape of the patch. Patch dynamics also refers to changes in the structure, function, and composition of individual patches that can, for example, effect the rate of nutrient cycling.

Patches are also linked. Although they are separated from other patches, migration occurs from one patch to another. This migration maintains the population of some patches, and can be the mechanism by which some plant species spread their seeds. This implies that ecological systems within landscapes are open, rather than closed and isolated. (Steward, 2006)

[edit] Conservation Efforts

Recognizing the patch dynamics within a system is needed for conservation efforts to succeed. Successful conservation includes knowing how a patch changes and predicting how they will be affected by external forces. These externalities include natural effects, such as land use, disturbance, and [succession], and the effects of human activities. In a sense, conservation is tha active maintenance of patch dynamics. (Steward, 2006)

[edit] Multiphysics Modeling

Patch Dynamics is also a term used in physics to bridge, using algorithms, the models describing macroscale behavior and to predict large-scale patterns in fluid flow. It uses locally averaged properties of short space-time scales to advance and predict long space-time scale dynamics.

In patch dynamics and finite difference approximations, the macroscale variables are defined at the grid points of a mesh chosen to resolve the solution. The standard PDE adaptive grid methods can be used to resolve gradients in the macroscale solution. Both patch dynamics and finite difference methods generate time derivatives mesh points; these time derivatives then help advance the solution in time. [3]

[edit] External links

[edit] References

  • Forman, R.T.T. 1995. Land Mosaics: The Ecology of Landscapes and Regions. Cambridge University Press, Cambridge, UK.
  • Groom, Martha J., Meffe, Gary K., Carroll, Ronald. 2006. Principles of Conservation Biology, Third Edition. Mosaics and Patch Dynamics by Steward T.A. Pickett