Ecology: Biology of Interaction. V-03. Ecological Classifications of Ecological Factors Proper

V-3. Actual Ecological Classifications of Environmental Factors In the previous section, we considered the classification of environmental factors by their origin (physical nature). As you understand, in many cases, completely different classifications are needed that reflect the role of factors for the organisms being considered. One of the most important such classifications, applicable specifically to ecological factors, is the subdivision of factors into conditions and resources (French ressource - auxiliary means). Resources are consumed by organisms and are thereby expended and depleted, while conditions affect organisms, can be changed by them, but are not expended and cannot be depleted. Resources correspond to certain quantities that decrease as a result of the organism's life activity. Ecological factors are not conditions and resources in themselves, outside of their connection with specific organisms (or other biosystems). For example, sunlight is a condition for humans and a resource for plants growing nearby. Plants compete for this resource, shading each other. In the dim light under the canopy of a dense forest, one can see that this resource can be significantly depleted: only shade-tolerant plants can be found on the ground and on the lower parts of tree trunks in such a forest. Even more surprisingly, the same factor can be a condition for one organism and a resource for the same organism in different ranges of values! For example, in nitrogen-poor soils, nitrates are an important resource for plants, as without nitrogen, plants cannot synthesize their own amino acids and other nitrogen-containing compounds. What happens if the amount of nitrogen salts in the soil increases? After a certain concentration of nitrogen salts, there will be more than enough as a resource. With a further increase in the concentration of nitric acid salts, they will begin to adversely affect the plant's metabolism. Finally, after a certain level, an excess of salts in the soil will make it difficult for water to enter the roots (due to the high osmotic pressure of the soil solution). In this case, it is clear that the nitrate content in the soil has become a condition, and an unfavorable one. Let's think: were we considering the effect of one or different factors on the plant? From a physical point of view - one: nitric acid salts in the soil solution. From an ecological point of view (from the perspective of their effect on plants) - different: a source of nitrogen nutrition (resource) and a factor of soil salinization (condition). For photosynthetic organisms (plants, cyanobacteria, etc.), sunlight is the most important resource. It is its energy that ensures the existence of the vast majority of biomass on the planet. However, chemosynthetic bacteria successfully carry out various redox reactions (e.g., oxidizing hydrogen, hydrogen sulfide, Fe2+ to Fe3+) where they find contact zones between reducing and oxidizing agents. Organic compounds created by autotrophs are sources of matter and energy for heterotrophs. The second most important group of resources for living organisms are various chemical elements necessary for the development of organisms - biogens. These include about half of the 54 elements found in nature. In addition, for organisms that form terrestrial ecosystems, the availability of water, carbon dioxide, oxygen, free space, and other organisms in the environment is extremely important. The most important conditions that most affect ecosystems are temperature, air humidity, pH, salinity, current, and various pollutants. Other classifications of ecological factors are possible (in the narrow sense of the term, which differs from environmental factors). For example, by their importance for organisms, factors can be divided into requisites (Latin requisitum - necessary) - mandatory factors without which the existence of organisms is impossible, and accessories (French accessoire - auxiliary details) - factors whose effect is not vital. Probably, the reader is working with this text while in some room. The presence of sufficient oxygen in the air is a requisite, while the aesthetic beauty of the walls is an accessory. Not all requisites are equally important for an organism. Among them, limiting factors can be distinguished. A limiting factor is defined as a factor whose small changes cause the greatest effects on the considered biosystem. As a result of this property, limiting factors determine the limits of development or distribution of organisms and other biosystems (for more details, see sections V-6 and V-7). Considering the above, when describing a specific situation, factors can be divided into favorable, limiting, and insignificant. We will consider different classifications of relationships between species, which can also be included in ecological factors, during the study of population ecology. In addition, for population ecology, the subdivision of factors into population density-dependent and population density-independent (or, equivalently, regulator factors and modifier factors) is important.