Figure 8.13 Competition between two laboratory populations of Paramecium with similar requirements.

Example 2 of the competitive exclusion principle or Gause s principle: Geospiza spp. We can go to Darwin's finches again to see examples of character displacement on the Galapagos Islands. Members of the genus Geospiza are wide spread among the islands. Geospiza fortis, for example, is found alone on Daphne Island, while G. fulginosa is found alone on Crossman Island. Both ground-feeding birds are about the same size. On Charles and Chatham Islands, on the other hand, the species co-exist. Although G. fortis is about the same size as their relatives on Daphne, G. fulginosa is considerably smaller than their neighbors on Crossman. The shift in size allows the G. fortis to feed on smaller seeds, thus avoiding competition with the larger G. fortis on Charles and Chatham. This and other documented cases of character displacement suggest that competition is important in shaping ecosystems. Displacement is interpreted as evidence of historical competition.

Example 3 of the competitive exclusion principle or Gause s principle: squirrels in England (http://www.saburchill.com/IBbiology/chapters02/035.html) The red squirrel (Sciurus vulgaris) is native to Britain but its population has declined due to competitive exclusion, disease, and the disappearance of hazel coppices and mature conifer forests in lowland Britain. The grey squirrel (Sciurus carolinensis) was introduced to Britain in approximately 30 sites between 1876 and 1929. It has easily adapted to parks and gardens replacing the red squirrel. Today's distribution is shown below in Figure 8.14.

Grey Squirel

Red Squirel

Grey Squirel

Red Squirel

Figure 8.14 Actual distribution of two Sciurus species in Britain.

The niche theory at the light of ecosystem principles

In general terms, Hutchinson's niche theory considers that the fundamental niche (theoretical) of a given species comprises all the combinations of environmental conditions that permit an individual of that species to survive and reproduce indefinitely. But from all these possible combinations, only the ones where the species is competitively dominant will in fact be utilized, constituting the realized niche. There will be of course limits of tolerance, maximum and minimum, of the organisms with regard to each environmental variable, which constitute the niche breadth.

This formulation, designed for use at the species and individual levels, is clearly compliant with the Ecological Law of Thermodynamics. In fact, what is said can be translated as: under the prevailing circumstances the organisms will attempt to utilize the flow to increase its Exergy, moving further away from thermodynamic equilibrium (Jorgensen, 1997), or alternatively in combination with the evolutionary and historically accumulated information, it will attempt to utilize the flow to move further away from the thermody-namic equilibrium (de Wit, 2005).

If the populations of two species occupy the same resources niche one of the two will become out competed, in accordance with the CEP (Gause, 1934), which states that no two species can permanently occupy the same niche. In trophic terms, in the absence of competitors, a given species will most probably specialize less than it will in competitor's presence (competitive release). This also clearly complies with the Ecological Law of Thermodynamics and can be translated as:

If more combinations and processes are offered to utilize the Exergy flow, the organization that is able to give the highest Exergy under the prevailing circumstances will be selected (Jorgensen, 1997), or alternatively as if more combinations and processes are offered to utilize the free energy flow, the organization that is able to give the greatest distance away from thermodynamic equilibrium under the prevailing circumstances will be selected (de Wit, 2005).

All the three examples illustrating the CEP can in fact be explained at the light of the Ecological Law of Thermodynamics.

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