The model ecosystem within the mesocosm (e.g., the right-hand side of Figure 1) is developed and maintained through managed self-organization of the ecological components that are added to the system. These additions include materials that provide structural support for organisms and initial conditions for biogeochemical cycles (soils, rocks, water, chemicals), along with species populations. All of these additions interact over time within the containment structure to form the model ecosystem. Additions are usually made directly from examples of the analog ecosystems though sometimes commercial sources are used, for example, if the analogs are fragile or endangered and removal of species is prohibited. Self-organization of the biota is facilitated by supplying an excess number of species populations so that selection processes produce a species composition that can survive and hopefully reproduce within the context of the mesocosm environment. This practice of species additions has been termed multiple seeding. When mature, mesocosms tend to have high biodiversity at the family and genus level rather than the species level, suggesting that wild systems develop their alpha diversity from multiple patches. Ecosystem modeling can therefore be successful at the patch or mean patch size. The selection processes that act on organisms are the mechanisms of ecological self-organization, and self-organization in a mesocosm is the sum of selection forces acting on species from both the model ecosystem and the engineering components of the mesocosm. Selection forces occur along the pathways of interactions. In natural ecosystems these interactions are between species and the environment and between species and other species. In the model ecosystem of a mesocosm, interactions between species and the engineered components add to the interactions found in the natural analog. Therefore, mesocosms can be even more complex than natural ecosystems, at least at small scales!
Self-organization occurs automatically and autonomously within the mesocosm because it is a living system but the self organization process can be managed by the human operator in order to achieve a desired species or biogeochemical composition. This human management involves the adjustment of environmental parameters and the addition and/or removal of certain species or chemicals. Thus, the model ecosystem needs to be monitored continuously and adjusted as necessary so that the ecological structure and function matches with the natural analog.
Many ecosystems include large animals that require large areas to support and that effect the ecosystem through top-down actions of physical disturbance or predation pressure (such as sharks, elephants, jaguars, etc.). Of course, these species cannot be included in a mesocosm-sized system, which represents a small fragment of a larger natural analog. The human manager can take the place of these large animals and can simulate their effects within the system as appropriate for the purpose that the mesocosm is intended to serve. Effects ofphysical disturbances, such as fire or storms, have also been simulated by human managers in mesocosm ecosystems.
Ecological engineering of mesocosms is similar to restoration ecology in many respects, since both practices have the goal of creating ecosystems that match natural analogs. Mesocosms match natural analogs in artificial settings while restored ecosystems match natural analogs in field settings. Because of this common goal, the self-organization properties of ecosystems are employed for both the creation of a mesocosm and the restoration of a damaged natural ecosystem.
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