During 20th century the majority of researchers interpreted ecological optimum as a certain combination of ambient factors which is optimal for growth, existence and reproduction of an organism. However, it was revealed in many species, that the maximum rates of various processes in an organism are achieved at various combinations of values of different factors, and under variable regimes as opposite to constant regimes. One may state that there is no well defined general concept which takes into account a bulk of data that do not conform the traditional definition of ecological optimum. Here, we show that it is necessary to make distinction between concepts of "static" and "dynamic" optima. It is needed for definition of real ecological optimum and creation of optimum conditions for given factor. We show also that it is necessary to take into account so-called delayed effects of factors. Basing on the analysis of responses of zooplankton to various temperatures and phosphoric load, we show that an optimum has "dynamic" characteristics besides previously known "static" ones, like a range of factor values on tolerance curve or a doze of factor. These "dynamic" characteristics are cyclic and stepwise changes of a factor, a directionality of factor's dynamics in case of stepwise changes and additionally, we reveal stimulating and inhibiting delayed effects of factors. Our results allow for a more detailed concept of ecological optimum, and also may stimulate investigations of quantitative contribution of various parameters of environmental factors to an ecological optimum of an organism or population.
Key-words:temperature, ecological optimum, Cladocera, stepwise changes, prolonged effects, realized niche Laboratory experiments with natural zooplankton communities were carried out to study the effects of two contrasting temperature regimes: constant temperature (15, 20, and These results support the previously formulated hypothesis that, in determining the ecological temperature optimum of a species within a natural community, it is not enough to define its optimum from constant, cyclic or random temperature fluctuations, but also from unidirectional stepwise changes in temperature. These stepwise changes may also induce prolonged or delayed effects.
RÉSUMÉEffets de changements graduels en température sur la dynamique de quatre espèces de cladocères
Mots-clés :température, optimum écologique, Cladocère, changements graduels, effets prolongés, niche « réalisée » de D. brachyurum et Ch. sphaericus, tous les deux sténo-thermophiles, était stimulé seulement par une température élevée stable (25 • C). Ces résultats confirment l'hypothèse formulée auparavant que, dans la détermination de l'optimum thermique d'une espèce d'une communauté naturelle, il ne suffit pas de définir son optimum à partir de températures constantes, ou de fluctuations cycliques ou aléatoires, mais aussi par des changements de température graduels. Ces changements graduels peuvent également produire des effets prolongés ou retardés.
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