A review of and some comments on the attempts to construct an overarching theory of ecosystems plasticity

It is generally accepted that life uses two distinct mechanisms during adaptation to the environment: evolutionary and individual. The latter is known as phenotypic plasticity. However, several decades ago, a conviction emerged and later strengthened that populations and ecological communities also tend to stabilize the essential variables (total biomass, productivity, adaptability, etc.) to a certain degree, regardless of uncertainty of environmental conditions. A response to this uncertainty is a change in the frequency of preadapted genotypes and compensatory fluctuations in population sizes. Adaptation can be regarded as a never-ending multilevel hierarchical process of individual-, population- and community-level adjustments to a changing environment. According to these concepts, adaptation is like a process during which individuals, populations and entire communities can adjust their optima to the ever-changing environmental conditions. Individual and populational rearrangements are means for a more subtle adjustment of the community optimum and the lines of defence, one following the other, on the road of stressful impacts towards the essential variables of an ecosystem. The authors of this conception, e. g. M. Conrad, V. N. Novoseltsev, H.-R. Gregorius, E. Lekevicius, also believe that these mechanisms should interact in a quite determined manner; this brings us hope that a unified theory on the plasticity of ecosystems will be developed. In this review an attempt is made to describe these concepts which are still in development and to reveal their strong, well-founded aspects as well as weak points. It is concluded that the multifarious attempts to falsify the conception are needed.