Ecology: Biology of Interaction. 5.03. Proper Ecological Classifications of Ecological Factors
One of the most important classifications is the division of ecological factors into conditions and resources. Resources are consumed by organisms and are therefore depleted and exhaustible, whereas conditions influence organisms, can be modified by them, but are not consumed and cannot be exhausted.
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5.02. Classification of environmental factors by origin
D. Shabanov, M. Kravchenko. Ecology: The Biology of Interaction Section 5. Autecology and Fundamentals of Environmental Science
5.05. Subenvironments and adaptations to them
5.03. Ecological Classifications of Ecological Factors The previous section discussed 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 under consideration. One of the most important such classifications, applicable specifically to ecological factors, is the division of factors into conditions and resources (French 'ressource' - auxiliary means). Resources are consumed by organisms and are thereby depleted and exhausted, while conditions affect organisms, are often changed by them, but are not consumed and cannot be exhausted. Resources correspond to certain quantities that decrease as a result of the organism's life activity. Factors are not conditions and resources in themselves; they are such only for specific organisms. 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 dense forest canopy, one can see that this resource can be significantly depleted: only the most 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 within different ranges! For example, on 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, nitrogen salts will be more than sufficient. With a further increase in the concentration of nitric acid salts, they will begin to have an adverse effect on the plant's metabolism. Finally, after a certain level, the excess salts in the soil will hinder the uptake of water by the roots (due to the high osmotic pressure of the soil solution). In the latter case, it is clear that the nitrate content in the soil has become a condition, and an unfavorable one at that. However, let's think: did we consider the effect of one factor 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 soil salinization factor (condition). For photosynthetic organisms (plants, cyanobacteria, etc.), sunlight is the most important resource. It is its energy that sustains the existence of the vast majority of biomass on our planet. However, chemosynthetic bacteria successfully carry out various redox reactions (e.g., oxidizing hydrogen, hydrogen sulfide, Fe2+ to Fe3+) where they find zones of contact 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 - biogens. They include about half of the 54 elements found in nature. In addition, for organisms that form terrestrial ecosystems, the presence of water, carbon dioxide, oxygen, free space, as well as other organisms in the environment is extremely important. The most important conditions that most significantly affect ecosystems are temperature, air humidity, pH, salinity, current, and various pollutants. Other classifications of ecological factors (in the narrow sense of the term, which differs from environmental factors) are possible. 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 action is not vital. Perhaps 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 decoration 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 have the greatest impact on the organisms under consideration and which, therefore, determines the limit of their development or distribution (see sections 5.6 and 5.7 for more details). Given 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 among ecological factors, during the study of population ecology. In addition, for population ecology, the division of factors into those dependent on population density and those independent of population density (or, equivalently, regulator factors and modifier factors) is important. Additional materials: Educational model: Ecological factors
5.02. Classification of environmental factors by origin
D. Shabanov, M. Kravchenko. Ecology: The Biology of Interaction Section 5. Autecology and Fundamentals of Environmental Science
5.04. Subenvironments and adaptations to them