The boundaries of an ecosystem determine the extent of the various processes occurring within the ecosystem. Note that we say processes (plural); in fact, there are many processes operating in parallel as contributors to the effective natural selection result. Also, there are actually boundaries (plural) to be found within an ecosystem. Several boundaries may result in a single function, or one boundary may achieve several functions.

Consequently, we will also speak of the parameters that define an ecosystem’s functions rather than its boundaries. A well specified set of ecosystem parameters allows the characteristics of the species it contains to be assessed by the applicable selection processes at work. Certain parameters of distinct ecosystems are geographic in nature and are perhaps easiest to understand when they present themselves this way. Darwin observed that the Galapagos Islands formed a closed ecosystem for many of the terrestrial animals found on it. His epiphany was that some of the species he observed actually existed because they had characteristics that particularly suited them to this ecosystem. They had evolved as variants of species that he had observed elsewhere, but based on their needs for survival in this ecosystem, they exhibited different characteristics than had been the case elsewhere. So, the geographical boundary of the Galapagos Island ecosystem is the water of the Pacific Ocean that surrounds the island. At least, the ocean waters form the boundary for the land based species and the amphibious species that are unable to bridge the waters to the mainland by swimming. For avian species, however, the ocean doesn’t necessarily provide a fixed barrier. Here, we see that the concept of parameters of an ecosystem is more adequate than a boundary. It is the parameter that allows the boundary to be hard for some species and yet soft for others. The function of the boundary varies with the parameter. This allows the ecosystem definition to be tailored to each species.

As we noted earlier, many wetlands areas provide ecosystems that are distinct from surrounding areas, but ecosystems where a boundary is formed, not by a lack of water, but by a change in the water characteristics of the area. That is, a wetlands area typically features standing or at least slowly moving water with some consistent water source and drainage area. The standing water may well be home to varieties of vegetation that thrive in the constant water source, but by the water being constantly recirculated, it contains the necessary nutrients and gases to support many species of plants and animals. In such an ecosystem, for many species a parameter might be established by the presence or absence of water, or by water with particular characteristics; for example, a specific oxygen content range, a particular salinity or a particular temperature range.

In high altitude areas, the temperature and air pressure which vary with altitude may form parameters of an ecosystem for some species. This is particularly true for many species of trees, with the average temperature gradient parameter forming the timberline boundary above which trees don’t grow. In coastal bays and inlets, ecosystems may be established by the parameter showing the salinity of the water, with certain species of fish and shrimp migrating in rainy seasons to track the high saline areas as the rivers pour fresh water into the bays.

The common characteristic of any specific parameter of an ecosystem is that it delimits some aspect of the natural selection process. In the case of pure geography, an island for example, the physical land area affects the ability of the various species contained within it to either enhance or diminish their potential for interaction with other species. The rabbits are constrained with the foxes if you will. At its most basic, this geographic boundary mandates that the rabbits will compete with each other for the available vegetation and the foxes will compete with each other for the available rabbits. If the rabbits eat all the available vegetation then they will become extinct and thereby remove the food source for the foxes, rendering them extinct as well. We can also consider the abilities of various species to modify the effects of a parameter. Consider birds. In some ecosystems, birds lay and hatch their eggs directly on the ground. In other areas, various species will build nests of sticks, straw and other material high in the canopy of the tallest trees. In

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