The Fundamentals of Pathosystem Balance

Pathosystems balance must be considered in terms of both macro-evolution and micro-evolution. Let us consider macro-evolution first.

For any existing wild plant pathosystem, it can be irrefutably asserted that the host has survived macro-evolutionary competition, in spite of the damage caused by the parasite. Furthermore, it can be asserted equally forcefully that the parasite has survived macro-evolutionary competition, in spite of the resistance of the host. This is a core argument, and it is, perhaps, the most fundamental aspect of any theoretical study of parasitism.

At the micro-evolutionary level, it can be asserted that any existing wild plant pathosystem must have survived the many vagaries and fluctuations of ecological (i.e. micro-evolutionary) competition, throughout its long macro-evolutionary history. Possibly the most important aspect of ecological competition is the occasional freak season which so favours the parasite that the host population is devastated. Pathosystem survival means that neither the host nor the parasite has at any time seriously impaired the ecological competitive ability of the other.

From these assertions, we can reach a conclusion that is, perhaps, self-evident. Wild plant pathosystems are balanced, stable systems. This conclusion enables us to identify the components of pathosystem balance with some confidence.

Pathosystem balance is a dynamic equilibrium between the survival requirements of the host species, and the survival requirements of the parasite species. Neither species threatens the survival of the other. This equilibrium is both ecologically stable, and evolutionarily stable. That is, neither organism threatens the competitive ability of the other, in either short-term ecological periods (historical time), or in long-term evolutionary periods (geological time).

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