Fundamentals of Evolution - Korzh O.P. - 2006

Part II. MACROEVOLUTION

Chapter 15. Megaevolution

15.4. Concepts of Evolutionary Ecology

Different scientists attribute varying meanings to the term "evolutionary ecology". Some maintain that discussing the evolution of ecosystems is altogether pointless. This is explained, on the one hand, by the fact that ecosystems, unlike living organisms, are incapable of reproduction or interbreeding and lack certain other characteristics of living systems. On the other hand, the very idea of biosphere evolution is rejected on the grounds that all types of ecological exchange—which enabled the establishment of matter and energy cycles—formed within it right from the beginning. Subsequently, only the organisms occupying specific energy levels changed, while the functional Structure remained practically unaltered. There are even views that regard the evolution of eukaryotic and Multicellular Organisms as a "redundant superstructure" that merely hinders the normal functioning of a perfect bacterial biosphere.

Today, the two most prevalent approaches to The Development of this scientific field are:

1) The Study of The Significance of ecological factors in the evolutionary process;

2) the investigation of the evolution of ecological life forms (communities, biocenoses, encompassing the biosphere).

According to the second approach, evolutionary ecology investigates the same systems as general ecology, but does so in their developmental aspect—specifically, how the relationships between living systems and their environment change over Earth's history. Recently, yet another approach has emerged: the establishment of synthetic evolutionary ecology, which relies not only on the synthesis of ecology and evolutionary theory, but also on their integration with bio-, geo-, and socio-ecology (V.S. Golubev).

According to Yu.I. Chernov, three fundamentally distinct processes are closely interrelated in the historical development of life:

1) speciation and the evolution of individual Organism groups (phylogenesis);

2) The formation of taxon compositions in particular regions or natural Zones of the Earth (floro- and faunogenesis - biotogenesis);

3) the transformation of communities and ecosystems. The first process constitutes the core content of evolutionary theory, the second—historical biogeography, and the third—evolutionary ecology. Currently, as Yu.I. Chernov asserts, the majority of scientists reduce the question of community evolution to the adaptive transformations of organisms within communities.

Within any biological unity, changes in The properties of one of its constituent parts correspondingly alter the CHARACTERISTICS OF THE system as a whole, whereas the properties of any component are realized in accordance with the needs of the unity as a whole and are therefore never fully utilized.

Quite often, the progressive character of evolution on Earth is associated with the Development of the biosphere. In this context, the progress of evolving systems is viewed as an increase in the "margin of stability"—the capacity of systems to function under changing environmental conditions. Throughout evolution, the integrity of The Biosphere as the highest level of integration of life increases (I.I. Schmalhausen's rule on the increasing degree of integration of biological systems). Nature tends to create stable systems regardless of their productivity. The Evolution of the biosphere in the pre-anthropogenic period proceeded both "horizontally" (the evolution of biodiversity) and "vertically" (the progress of evolutionarily more advanced elements). At the same time, sustainable development along the "vertical" axis was ensured by maximal biodiversity.

In accordance with the compaction and complexification of the biosphere, its buffering capacity increased. This is manifested both in the enhanced resistance of the biosphere to various abiotic factors and in the retardation of speciation processes. The strengthening of the biosphere's buffer properties transforms it into a well-regulated system that provides its constituent components with relatively stable conditions for existence. For the emergence and spread of new organisms, mere viability is no longer sufficient—they must possess superior viability compared to ancestral forms.

All evolution on Earth has been driven by the ADAPTATION OF ORGANISMS not only to the inanimate external environment, but also to one another. As a consequence, the components of individual biogeocenoses turn out to be well-balanced. However, the mechanisms governing such balanced systems remain unknown for now.

Unfortunately, it remains relevant today that science is still incapable of explaining the principles of ecosystem evolution. Presently, the question regarding the smallest elementary biochorological unit within which ecosystem evolution takes place cannot even be considered resolved. For instance, N.V. Timofeeff-Ressovsky identified this unit as the biogeocenosis proposed by V.N. Sukachev, within which, on the one hand, the geochemical processes of the biosphere driven by Living organisms are carried out,

and on the other hand, elementary evolutionary phenomena arise and the triggering mechanisms of evolution operate. Today, however, the question is raised (P.P. Vtorov, N.M. Drozdov) that METABOLISM/2.html">THE CONCEPT OF "biogeocenosis" is considerably narrower than that of "ecosystem". A biogeocenosis is limited solely to the level of a community concentrated within a plant association (the smallest typological unit of phytocenoses). Landscape understanding corresponds to much larger and more complex ecosystems. The biosphere can also be regarded as a giant planetary ecosystem. Ecosystems of various Levels of Organization are capable of evolution, and a direct link can be traced between the evolution of individual, smallest ecosystems and that of the biosphere as a whole. A complex scheme of interrelated and hierarchically subordinated structures emerges: Changes in the functioning of lower tiers directly affect the stability and viability of the entire system.

It is arguably impossible to explain the evolution of the biosphere without catastrophe theory. This can be linked to the fact that the Homeostasis of the biosphere as a whole is capable of counteracting certain local deviations from the norm, which constitutes the formation of Primary and secondary successions.

A radical change in The structure of the biosphere requires profound, prolonged shifts in the entire complex of ecological factors—on the scale of an ecological catastrophe. Even the formation of individual landscapes is often the result of catastrophic transformations, at least of a local nature. The formation of steppes and the reduction of forest areas in the past can only be associated with significant climate changes (aridization), while The Emergence of deserts is frequently viewed as a consequence of human intervention in the functioning of open landscapes (the Sahara Desert is the result of overgrazing by livestock in ancient civilizations).

One of the features of biosphere development is the alternation of periods of relatively calm development with periods of turbulent form-generation (unique revolutions in the biosphere, according to N.M. Kamshilov). This indicates the endeavor of living matter to break free from the control of competition and natural Selection. The colonization of new ecological conditions for development (adaptive radiation) is an example of reduced competition. At the same time, the realization of such a trend leads to a succession of periods when the pressure of the Struggle for Existence is relaxed followed by periods when it is intensified, and when certain forms of competition are replaced by others that are more complex.

V.A. Krasilov proposes the following explanation for fundamental changes in the species COMPOSITION OF THE biosphere: under certain steady-state conditions, dominant groups develop, which is accompanied by their adaptive radiation and a corresponding level of specialization. For various reasons, destabilization of the biosphere may occur, primarily manifesting as planetary-scale climate shifts (for instance, the breakup of the supercontinent Pangea first into Gondwana and Laurasia, and subsequently into modern continents, led to the formation of latitudinal climate gradients). The consequence of such changes is the extinction of "surplus" species: dominant forms prove maladaptive under changed conditions, leading to the near-simultaneous extinction of many representatives across the most diverse habitats—something that cannot be explained by disease, poisoning, competition, or similar factors. Cosmic theories (such as The impact of a large meteorite) are likewise insufficient, as The rate of disappearance of most taxa in such a scenario would have to be significantly higher.

Another point that deserves attention is a certain periodicity in mass extinctions of organisms (although different scientists propose varying periods). To summarize, it can be stated that The problem of ecosystem evolution remains unresolved to this day, and existing explanations are still merely conjectural.