MEDICAL BIOLOGY, ANATOMY, HUMAN PHYSIOLOGY AND PATHOLOGY - Ya.I. Fedoniuk 2010

BIOLOGY

CHAPTER 2. BIOGEOCENOTIC LEVEL OF ORGANIZATION OF LIFE AND HUMAN PLACE IN IT

2.1. FUNDAMENTALS OF HUMAN ECOLOGY

Biogeocenosis as an ecological system

In nature, populations of organisms of various species always form biocenoses. A biocenosis is a historically established assemblage of animal, plant, and microorganism populations that occupy a land or Water surface area with uniform abiotic conditions. The animal component of a biocenosis is called a zoocenosis, the plant component a phytocenosis, and the microorganisms a microbiocenosis. The boundaries of a biocenosis are primarily determined by the phytocenosis; for example, the biocenosis of a pine forest. A land or water surface area with uniform abiotic conditions occupied by a specific biocenosis is called a biotope. Together, the biocenosis and biotope constitute a biogeocenosis. A biogeocenosis is a historically formed complex of living and non-living components within a specific area of the Earth's surface, interconnected by the exchange of matter and energy. The biocenosis represents the living part of the biogeocenosis, whereas the biotope represents the non-living part. The term "biogeocenosis" was first introduced into science in 1940 by the Russian scientist V.M. Sukachev. It is closely related to the term "ecosystem," which had been proposed earlier in 1935 by the English botanist A. Tansley. The difference between them is that an ecosystem is a broader concept. Ecosystems do not have fixed boundaries and can encompass spaces of varying scales: from a water droplet or an aquarium to the ocean or the entire surface of the planet. In contrast to an ecosystem, the boundaries of a biogeocenosis are largely defined by its phytocenosis.

A biogeocenosis is the elementary structural unit of the biosphere. It forms the biogeocenotic level of the Organization of living matter. The laws governing the functioning of a biogeocenosis, its Structure, productivity, dynamics, boundaries, and the cycling of matter and energy are studied by the science of biogeocenology. Individual biogeocenoses may include pathogens, vectors, and reservoirs of diseases. Therefore, The Study of biogeocenoses is of great importance for medicine and pharmacy in understanding The Nature of natural foci of diseases.

The non-living component of a biogeocenosis (the biotope) includes inorganic substances, topography, soil, microclimate, the gas COMPOSITION OF THE air, and so on. The living component (the biocenosis) comprises three mandatory groups of organisms: 1) producers; 2) consumers; and 3) decomposers. Producers are autotrophic organisms that synthesize organic substances from inorganic ones (green plants). Consumers are heterotrophic organisms that cannot synthesize Organic compounds from inorganic precursors and instead feed on ready-made organic matter without mineralizing it. Decomposers (destruents) are heterotrophic organisms that break down the organic remains of dead plants and animals and convert them back into Mineral Substances (for example, saprophytic Bacteria).

A biogeocenosis is an open system. Its primary function is the cycling of matter and energy. It receives solar energy, soil minerals, atmospheric gases, and water, while releasing heat, oxygen, carbon dioxide, and biogenic elements. The Circulation of matter and energy within a biogeocenosis occurs through trophic chains. A trophic chain (food chain) is a sequential series of living organisms linked by nutritional relationships. Any food chain consists of several trophic levels, each of which can simultaneously comprise many species of organisms. The trophic structure of a chain reflects the direction of energy transfer within it.

The primary source of energy upon which the existence of all organisms on Earth depends is the Sun. The first link (the first trophic level) in the food chain consists of green plants (producers) that absorb solar energy during Photosynthesis and convert it into the potential energy of the organic compounds they synthesize. However, only a negligible fraction (about 1 %) of the solar energy reaching Earth is captured during photosynthesis, while the rest is dissipated as heat. Animals that feed on green plants (primary consumers) also assimilate only a small fraction of their food energy (10-20 %) to build their biomass, with the remainder being lost as heat through metabolic processes; they form the second trophic level. The same applies to predators (secondary consumers) that feed on herbivores, forming the third trophic level. Consequently, with each successive trophic level, The amount of assimilated energy in the food chain progressively decreases. This pattern is known as the ecological pyramid rule. The decrease in energy at each subsequent trophic level is accompanied by a reduction in biomass and the number of individuals, which limits the number of links in a food chain (typically to no more than four or five). Examples of food chains include: 1) planktonic Algae — planktonic animals — crustaceans — fish — fish-eating birds and mammals; 2) plants — insects — insectivorous birds — birds of prey. An ecological pyramid is a graphical representation depicting The sequence of trophic levels in a food chain. Pyramids are categorized into energy pyramids, biomass pyramids, and pyramids of numbers.

Within a biogeocenosis, numerous food chains are formed and intricately interconnected, as the same species can be part of multiple chains. By intertwining, food chains form a food web. The existence of the food web ensures the relative Stability of the biogeocenosis. If the population of a certain species declines or disappears, equilibrium in the system is not disrupted because species that fed on it can switch to alternative food sources. The greater the species diversity of a biogeocenosis, the more stable it is.

A biogeocenosis is characterized by the following parameters: species diversity, population density, biomass, and biological productivity. Biological productivity is the amount of biomass generated per unit of time. A distinction is made between Primary and secondary productivity. Primary productivity is the biomass produced per unit of time by autotrophic organisms, whereas secondary productivity is the biomass generated by heterotrophic organisms over the same period. The productivity of natural biogeocenoses cannot fully meet humanity's needs for essential products. Therefore, humans create artificial biogeocenoses—agrobiogeocenoses (fields, pastures, vegetable gardens, orchards, reservoirs). Although more productive, these systems cannot persist without ongoing human maintenance and are inevitably destined to be rapidly replaced by natural biogeocenoses if abandoned.