| Abstract: | The notion of ecological optimum is discussed as related to aquatic poikilothermic animals. Publications on the analysis of the influence of thermal factor on vital functions of invertebrates with the subsequent statement of the general pattern of optimal environmental factors are reviewed. It is concluded that the optimum includes not simply the range of the factor's values on the tolerance curve or the dose of the factor providing for the most favourable life conditions, but the oscillations of the factor within the optimum range, i.e., the astatic optimum, as termed by Prof. A.S. Konstantinov. It is shown, by the example of the influence on organisms and populations of zooplankton of stepwise changes of temperature, increased doses of mineral phosphorus, and low-power laser radiation, that to determine the optimum of an environmental factor it is important to use not only its absolute values and the parameters of cyclic changes, but also the presence or absence of stepwise changes, also determining the direction of the dynamics and the duration of influence of the "dose", as well as the presence and character of the after-effects (inertial action) of the factor on organisms. It is suggested to introduce more detailed and concrete definitions to distinguish between the "static" and then "dynamic" optimum. The former includes the range of optimum values of the factor on the tolerance scale and the "dose" of every factor matching the organism's requirements and providing for the maximum favourable life conditions. The latter includes optimum parameters of cyclic changes (frequency and amplitude) of the factor, along with determining their position in the range of optimum values (at its lower, middle, or upper part), the presence or absence of stimulating effects of stepwise changes of the factor, including the duration of influence of some "dose" of the factor and the order of alteration of the higher and the lower values (dynamics direction), as well as the presence or absence and the character of after-effects (inertial action) of the factor on the organism. |
