Bolshakov V. Shvartz ecological rule – a look through decades // Principy èkologii. 2019. № 3. P. 4‒11. DOI: 10.15393/j1.art.2019.9642

Issue № 3

Analytical review

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Shvartz ecological rule – a look through decades

Introduction

In commemoration of the 100th anniversary of the birth of Stanislav Semenovich Schwartz (1919-1976), the academician of the USSR Academy of Sciences, the large international symposium "Ecology and Evolution: New Horizons" was held in Yekaterinburg on April 1-5 2019. S.S.Schvartz is an outstanding scientist of the XX century who made a significant contribution to the development of theoretical and applied ecological problems in our country. The symposium was attended by more than 300 people from many regions, scientific institutions, universities of Russia and a number of foreign countries. In the presented reports, the development of the ideas of the academician in modern ecology (2019) was discussed. When assessing his heritage, it should be emphasized that the concept of the term “ecology” in the years of S.S. Schwartz’s activity and now has changed significantly, not only in the perception of the scientific community, but by governing organizations and society as a whole. In recent years, the term “ecology” means a very wide range of problems. This was clearly evidenced by the “2017 year of ecology” in Russia: among the events there was everything – from the fight against unauthorized waste to the “ecology of dance”, but, unfortunately, there were practically no significant scientific publications developing fundamental ecological science, a striking representative of which was academician S.S. Schwartz.

 In my plenary report at the symposium, I emphasized that S.S. Schwartz belonged to that generation of scientists who defined ecology, first of all, as a biological science. In one of his most famous books – “Evolutionary Ecology of Animals” (1969) - he wrote: “…regardless of the known transformation in the views of biologists on the subject and method of ecology, its main task has remained unchanged for 100 years. This task is to study the life of animals and plants in their natural habitats.” Further he defines ecology “as a science that studies the relationship of animals with the environment at the population level,” noting that “ecology as a science of populations fills a significant gap in the fullness of knowledge of life on earth.” Ecology as a science of the nature’s life is now experiencing its second youth. Originating more than 100 years ago as a doctrine of the relationship “organism – environment”, ecology was transformed into the science of the structure of nature, the science of how the living cover of the Earth works and its integrity..

Analytical review

In the report at the symposium, I pointed out that academician P.L. Gorchakovsky – the colleague of S.S. Schwarz, after many years of work at the Institute of Plant and Animal Ecology of the Ural Division of the Russian Academy of Sciences (RAS) and in the editorial board of the journal “Ecology” (the founder and first editor of which since 1970 was S. S. Schwartz), called him a “forerunner of ecological thinking”. However, in my opinion, it is more correct to consider academician S.S. Schwartz in the first place as a “forerunner of population-ecological thinking,” since he gave populations a crucial role, defining ecology as the science of populations. He formulated and proved the position that "the population is the main, and for higher animals – the only form of existence of the species, which has all the necessary conditions for independent existence and development for an indefinitely long period of time and is able to respond adaptively to changes in the environment». The literature devoted to the development of the doctrine of populations and modern concrete data on the population structure of species is huge. The population idea of ​​S.S. Schwartz is currently in full demand, although, like the concept of "ecology", the term "population" has become widely used not only in biological, but also in other areas of science and society.

Citation analysis of publications of S.S.Schvartz from 1998 to 2017 in the RSCI (more than 4000 citations) shows that his ideas about populations and ecological mechanisms of evolution are of greatest interest to modern ecologists. Among the many ideas and propositions formulated by S.S. Schwartz and developed later, the opinion of the famous Polish ecologist K. Petrusevich deserves attention. His article “Schwartz Ecological Rule” was published in the anniversary issue of the journal “Ecology” (No. 2, 1979) dedicated to the 60th anniversary of the scientist. K. Petrusevich noted that on the basis of huge material on numerous morphophysiological indicators in dozens of species collected and processed by S.S. Schwartz and his students, the thesis was confirmed that “speciation is a distinct stage of adaptation, the formation of a new, more energy-efficient adaptation, so the specialized species are always better adapted than specialized intraspecific forms”. Since this phenomenon has an important general biological significance, K. Petrusevich proposed to raise it to the rank of “Schwarz Ecological Rule”.

Over the past 40 years, references to the article by K. Petrusevich and the term “Schwartz Ecological Rule” were of unit character. Meanwhile, the study of animals, intensively carried out both in the second half of the XX century and now in the most extreme conditions of their existence – in the Far North and in the highlands -  has provided a lot of material to confirm this "rule". It is appropriate to quote the words of the famous Soviet zoogeographer and ecologist A.A. Nasimovich: “For an ecologist, the study of highlands makes it possible to understand better the adaptive capabilities of animals ... In extreme conditions of highlands, as well as in the Arctic, Antarctica and parched deserts, where life has a less complex organization and the factors realizing it are more obvious, ecological studies are especially effective” (Nasimovich, 1964, p. 5).

 

At the time of S.S. Schwartz research was conducted personally by him and his students in the subarctic regions with the wide use of the method of morphology-physiological indicators, as well as in the mountains of the region, primarily in the Urals – from the Far North up to Kazakhstan (over 2000 km). For decades after the publication of the article of K. Petrusevich, numerous studies on the adaptations of mammals conducted beyond the Arctic Circle and in the diverse mountain systems of the Earth, completely confirmed the main idea of ​​S. S. Schwartz about the various nature of adaptations aimed to maintain the energy balance in species and intraspecific forms. During the life of S.S. Schwartz, a book was written and published (1972). It was based on his own research both in the Urals and in other mountainous regions (the Caucasus, Altai, mountains of Central Asia, etc.) and analysis of numerous literature data. In this book, the materials supporting and developing this most important general biological position of the evolutionary theory of ecological mechanisms of evolution were analyzed. In this aspect, mainly small mammals were studied: insectivorous, rodents, lagomorphs (mainly tree-creepers). That is connected, first, with the greater study of these groups and their availability to mass collections and group analysis, and, second, with their being confined to certain high altitude zones and habitats and the absence of significant vertical migrations in most species. Besides, representatives of these orders form the basis of the animals that inhabit various high-altitude mountain belts.

According to the distribution patterns, all mammals living in mountainous regions can be divided into two groups: 1) mountain species, 2) widespread species forming stable populations in the mountains. Our analysis of the world fauna of three orders of mammals that make up the basis of the population of mountainous regions (insectivorous, lagomorphs, rodents) showed that only a very small number of genera (mainly monotypic and characteristic of the fauna of the tropical zone) and species of mammals belong to the first group. Most small mammals found in the mountains are widespread species that inhabit various altitudinal zones (Bol’shakov, 1972).

Studies have shown that in the ways of adaptation of both groups to mountain conditions, along with the manifestation of common, similar patterns, there are significant differences. The similarity lies primarily in the development of biological features aimed at maximizing the use of territorial and food resources of the respective mountain zones in these groups. They are similar types of settlements and territorial groups, insignificant lability of daily activity indicators and a tendency to its increase in mountain areas, an increase in the variety of food consumed and the absence of strict food specialization, stocking of forage for the winter at unstable food base, the ability to deposit reserve nutrients not only in the form of fat, but also of glycogen, vitamins (primarily vitamins A and E). According to these signs, in animals of different altitudinal zones one can note some resemblance with animals living in similar landscape zones.

However, in the adaptation of mountain species and mountain populations of widespread species, fundamental differences are observed, mainly in ways to maintain optimal density and maintain energy balance.

The optimal density of mountain populations of widespread species is maintained due to the intensification of reproduction, which is provided by various mechanisms: an increase in the number of young in the brood, an increase in the breeding period, the number of generations, etc. In the vast majority of studied mountain species, the intensity of reproduction is much more stable and lower, although their potential, as our experiments have shown, is much greater than fecundity realized in natural conditions. Low intensity of reproduction of mountain species should be considered depending on the balance of populations with habitat resources, and not only with good protection of the latter and, therefore, lower mortality of mountain forms. The features of age structure and dynamics of mountain species abundance and mountain populations of widespread species, which have significant differences between the two groups, confirm this position. Experimental studies show that the reduced breeding intensity in some mountain species with a labile generative cycle (Tien Shan vole, Royle's mountain vole) is not a stable and firmly fixed feature, but is determined by very specific environmental factors. However, the low and stable number of young in the brood in mountain species should be considered as a hereditarily fixed property developed by natural selection. In mountain populations of widespread species, the number of young in the brood, on the contrary, is one of the most variable indicators that reflect the response of the species to specific environmental conditions.

The ways of maintaining the energy balance in mountain conditions are fundamentally different for both groups. Whereas in widespread species, the mountain dwelling is associated with an intensification of metabolism, which, in particular, is expressed in a complex of morphophysiological changes (an increase in the relative weight of the heart, kidneys, hemoglobin content, etc.), in mountain species, adaptation to mountain conditions is not accompanied by an increase in internal organs or an intensification of their functions. It can be assumed that in the adaptation of species biochemical changes play the leading role that makes excessive the pronounced changes in the anatomical features.

The analysis of modern literature shows that the specific mechanisms of adaptation of close species at the tissue level are still not clear enough, although the hypothesis of the biochemical essence of this process has been expressed repeatedly, including by S. S. Schwartz (Schwartz et al., 1964; Schwartz, 1969).

Subsequent research of many scientists on the study of both mountain species and mountain populations of widespread species in different mountain systems over the past decades has fully confirmed the positions stated above. In particular, they were especially intensively conducted in the Urals by the students and followers of S.S. Schwartz and in the Caucasus, scientists of the scientific school of the Associate Member of RAS A.K. Tembotov – A.K.Tembotov Institute of Mountain Territories (Nalchik). The results of these works are summarized both in numerous articles and monographs, as well as in the materials of regular conferences held by these institutes, for example, in 1977, 1982, 2002 in Sverdlovsk (Yekaterinburg) (Ecology, methods…, 1977; Ecological problems…, 2002), in Vorkuta (1989), and since 2005, regularly every two years – in the Caucasus (Maykop, Sukhumi, Nalchik) (Ecology of mammals …, 1997; Mountain systems …, 2005, 2017). Conferences are held on the study of mountain territories and their components, with the publication of materials confirming the validity of the generalization of the academician S.S. Schwartz in relation to mountain mammals (e.g., Mammals of mountain regions …, 2005; Baragunova et al., 2017, Bogtaeva et al., 2019). Similar patterns were established by S.S. Schwartz and his colleagues in the study of subarctic animals (Schwartz, 1963; Schwartz, Ishchenko, 1971). S.S. Schwartz convincingly showed that the exploration of the subarctic by many animal species occurs without noticeable changes in metabolic rate, and the metabolism level of typical autochthons of the North (Siberian lemming, Middendorfs vole, etc.) is even lower than in their related forms, the distribution of which is limited to more southern latitudes. In this case it was meant that in some small mammals in the conditions of the Far North, the increase in resistance to low temperature should be considered primarily  as an adaptation to low summer (rather than winter) temperatures (Schwartz, 1963). These studies are now considered classics and find their development in many scientific institutions of our country. So, we can call the work of Yakut scientists under the long-term leadership of N.G. Solomonov, the Associate Member of RAS .

In his article, K. Petrusevich cites his data on the relative heart weight of birds living in the North as proof of the conclusion of S. S. Schwartz, emphasizing that the heart index of Arctic species-autochthons practically does not differ from that of individuals of temperate widespread species: the heart index in Arctic populations is distinctly higher than in populations of the same temperate species, reflecting the same pattern as in mammals.  However, in relation to birds, the “Schwartz ecological rule” requires further research and clarification due to the extremely short breeding period of many bird species in the Far North, as well as to their migrations to the southern regions. At that, it is not clear to what conditions their adaptations should be considered. Similar comparative studies have not been carried out in recent years, although, the study on migrations, for example, of falcons nesting on the Yamal, to Iraq, where they live for at least 7-8 months, is carried out by employees of the Arctic Research Station (Institute of Plant and Animal Ecology, Ural Division of the RAS) in Labytnangi, Yamal-Nenets district.

Nevertheless, the question arises: the formulation of the “Schwarz ecological rule” is valid only for warm-blooded vertebrates (mammals and birds), or this pattern is also manifested in cold-blooded ones – amphibians and fish. Numerous studies of amphibians in the Subarctic, initiated personally by S.S. Schwartz and his colleagues showed that the determining factor here was the temperature of the environment.

If the compared groups of animals are correctly identified, if the assessment of their indicators is carried out in accordance with the requirements of statistics, then one can be confident in the reality of identifiable differences between groups of animals. This is the first and most important stage of research. Further work consists in the ecological analysis of the obtained data. Its essence is reduced to the comparison of morphological and physiological parameters of animals with their way and conditions of life. The more diverse the used material, the more interesting the conclusions obtained by applying the method of morphophysiological indicators.

In subarctic populations of amphibian, the growth and development rate are almost proportional to the temperature in subarctic latitudes, where water bodies completely freeze in winter, metamorphosis of frogs proceeds at a faster rate than in the southern regions. In all cases, this pattern is a population adaptation, and not a species one, since there are no specialized amphibian species in the Subarctic. A comparison of the amphibian adaptations at the population level was carried out in the Urals by the researchers of the Institute of Plant and Animal Ecology of the Ural Division of RAS in recent years.

Interesting studies on the discussed problem were carried out in the Urals on the settlement of the southern amphibian species – the lake frog. Accidentally introduced in the late 90-s of the XX century in reservoirs-coolers of thermal power plants of the Middle Urals, this species not only quickly adapted to new living conditions, but by now already actively inhabits the natural," cold " for lake frog habitats in the basins of the rivers Pyshma, Iset’, Sysert’, and others. At that, as detailed studies have shown, there are no noticeable changes in the biological characteristics of the Ural populations of the southern species - invader and populations of species characteristic of the Middle Urals (brown frog, moor frog). Specific adaptations to the environment in Ural species do not differ from those of southern species – this applies to the size of the clutch, the rate of development of tadpoles, life expectancy, etc. (Ivanova, 1995; Ivanova, Bolshakov, 2018).

The study of morphophysiological indicators in fish of the North (Ob basin), allowed S.S. Schwartz, L.A. Dobrinskaya, L.N. Dobrinsky (S.S. Schwartz, L.A. Dobrinskaya, L.N. Dobrinsky, 1965) to express the idea that between fish and terrestrial vertebrates there are some fundamental differences in the nature of the manifestation of the most common morphophysiological patterns. This is, obviously, primarily due to the fact that in fish, as later works showed, adaptations to the environment developed exclusively as adaptations to temperature (Golovanov, 2013). The manifestation of various forms of temperature adaptations occurs on the basis of physiological, biochemical, and behavioral reactions (Nemova, Vysotskaya, 2004).

 

Conclusions

Thus, the regularity formulated by S.S. Schwartz, which at the suggestion of the Polish academician K. Petrusevich was elevated to the rank of “Schwartz’s environmental rule”, was confirmed in long-term studies on the adaptations of mammals of mountain regions and the Far North. It is essential for the development of modern ideas about the ecological mechanisms of evolution. At the same time, this rule is not applicable for cold-blooded vertebrates, so in general it is advisable to perceive it as an empirical generalization after V. I. Vernadsky.

References