Ecology: biology of interaction. I-06. Regulation of biosystems

I-6. Regulation of Biosystems Life is a constant change, despite which most important parameters of living systems remain relatively stable. For example, in just one year, most of the atoms in each person's body change, yet the person remains practically the same. Over centuries, almost all organisms inhabiting a forest change, but the important properties of the forest may remain unchanged. What properties of biosystems ensure such stability amidst change? To answer this question, cybernetic (related to control science) concepts of feedforward and feedback are important. Feedforward is the influence of a factor on the system under study (example: by turning the steering wheel, the driver changes the direction of the car's movement). Feedback is the dependence of the control influence on the state of the system itself (example: the change in the car's direction of movement affects the driver's steering wheel turns). Thus, feedback is the control of a system taking into account its state, the dependence of the control influence on its results (Fig. I-6.1, A). Fig. I-6.1. Explanation of the concept of feedback. A. Feedforward and feedback. B. A non-biological example of feedback. Two types of feedback are distinguished. Positive feedback amplifies deviations of the controlled variable from its initial state, while negative feedback returns the system to its previous state. In other words, positive feedback is the mutual stimulation of two processes, and negative feedback is the suppression of deviations in the controlled process. Let's consider a simple example (Fig. I-6.1, B): a pot of water is boiling over a hot fire. If the fire burns very strongly, some water spills out, partially dousing the fire and reducing its intensity. When the fire dies down, the spilling stops, and the fire gradually flares up again. In this example, a deviation of the controlled variable (fire intensity) causes a change in the control factor (spilling) that has an effect on the controlled variable opposite (negative in sign) to the initial deviation. Thus, in this case, we are dealing with negative feedback. And in what case would feedback be positive in a similar example? If instead of water, there was kerosene in the pot! In this case, the brighter the fire burns, the more the kerosene will spill out, which will further intensify the burning of the fire. What will this lead to? The kerosene will spill out and burn... It is significant that in the example with the pot, positive feedback quickly leads the system out of its initial state (the pot with kerosene will empty), while negative feedback (if there is water in the pot) leads to the preservation of its properties relatively constant over a certain period. Negative feedback stabilizes the system, while positive feedback shifts it to another state (i.e., destroys the former structure of relationships). The existence of alternative operating modes of biosystems is determined by combinations of two types of feedback: negative feedback stabilizes each mode, while positive feedback ensures switching between these modes. For example, changes in ontogeny are controlled by positive feedback. This is how, for example, the development of infatuation occurs (switching from one behavioral program to another): a stimulus causes interest, interest intensifies the stimulus. Interest leads to certain actions, which also lead to an increase in the stimulus and interest, and so on. The process of courtship and rapprochement reaches its climax, after which the system transitions to another state... Usually, negative feedback can operate within a certain range of regulation. When this range is exceeded, positive feedback mechanisms come into play, destroying the system. Returning to the example of the pot on the fire, one can see that both a sharp increase in flame intensity and the dying out of the fire will take the system beyond the "corridor" within which its state is regulated by negative feedback. Let's give a more relevant example: an increase in atmospheric carbon dioxide concentration activates reactions that reduce it (enhances photosynthesis, increases binding as lime in the World Ocean). When the carbon dioxide concentration exceeds certain limits (e.g., with its excessive increase), mechanisms are activated that shift the system to another state. Rising temperatures due to the greenhouse effect cause a decrease in photosynthetic green mass, accelerated release of carbon dioxide from the soil, etc., which can lead to a further increase in CO2 concentration (and a transition of the system to another state with other negative feedback mechanisms stabilizing it). Biological systems can be viewed as cybernetic systems characterized by ordered internal interactions. In organisms, the control system is internal and specialized; in technical devices with negative feedback (servomechanisms), it is external and specialized; in ecosystems, it is internal and non-specialized (Fig. I-6.2). A typical feature of all cybernetic systems is that low-energy processes control high-energy processes (the movement of a hand on a switch stops a factory). At the organismal level, significant metabolic rearrangements can be triggered by just a few hormone molecules. In ecosystems, top predators, responsible for only a small fraction of the metabolism occurring in the ecosystem, can have the greatest regulatory impact on the community. Parasitoid wasps (see IV-6) transform a small fraction of the energy flow through the biocenosis but effectively regulate its net production through herbivorous insects. Fig. I-6.2. Features of negative feedback in a technical device (A) and an ecosystem (B). Regulation at different levels of biosystems is often carried out through negative feedback, which gives many biosystems similar properties. Here are a few examples of regulation based on negative feedback at different levels of biosystems (Table I-6.1). Table I-6.1. Examples of regulation based on negative feedback for different levels of biosystem organization.

Level	Table I-6.1. Examples of regulation by the principle of negative feedback for different levels of biosystem organization
	Level	Example of regulation by the principle of negative feedback	Process
Molecular	Negative feedback	Molecular	Regulation of enzyme activity
Cellular	A deficiency of the product leads to activation of the enzyme and intensification of its synthesis by the cell, and an excess leads to its inhibition and suppression of synthesis	Cellular	Interconnection between assimilation and dissimulation
Organ-tissue	An increase in the cell's energy expenditure leads to intensification of the processes through which it obtains this energy; a decrease in expenditure leads to suppression of dissimulation	Organ-tissue	Regulation of cell division in tissues
Organismal	Contacts between neighboring cells in tissues suppress their proliferation; the absence of neighboring cells and contacts with them stimulates the cell to reproduce	Organismal	Maintenance of body surface temperature in homeothermic organisms
Population	Cooling of the body surface leads to intensification of blood flow and restoration of the necessary temperature, and moderate heating leads to a decrease in blood supply to the surface	Population	Regulation of reproduction through territoriality
Biogeocoenotic	With excessive population density, a significant part of the individuals' energy is spent on territorial conflicts, and the number of offspring produced does not increase or even decreases; with a decrease in density, the opposite reaction is observed	Biogeocenotic	Biocenotic regulation of population density
Biospheric	With a decrease in population density, predators switch to other victims, conditions for parasite spread worsen, resources become more accessible; an increase in density causes opposite processes	Biospheric2	As the CO concentration rises2 photosynthesis and the binding of carbon dioxide in the form of lime in the ocean water intensify