Classification by relation to ecosystem and nature
For convenience of studying the environment, factorial ecology divides all impacts into several major groups. First of all, factors are evaluated by their position relative to the ecosystem itself:
- Exogenous (external) — forces that exert an effect on the biocenosis from the outside.
- Endogenous (internal) — phenomena originating directly inside the system under consideration.
Of fundamental importance is the division of factors according to the nature of their origin. Three global categories are distinguished here:
- Abiotic factors. These are all manifestations of non-living nature. They include physical climatic parameters (illumination level, temperature regime, precipitation amount) and non-climatic phenomena (e.g., radiation). This group also includes chemical parameters: the concentration of various substances in soil, atmospheric air, and water.
- Biotic factors. These represent the totality of influences of living organisms on each other. They encompass both intraspecific relationships of individuals and interspecific contacts.
- Anthropogenic factors. These are the consequences of human activity that cause physical, chemical, or biological alterations in the environment.
Influence of time on the formation of adaptations
How long and with what frequency a factor acts on living beings directly determines the ability of organisms to adapt to it. According to the duration of exposure, three types are distinguished:
- Constant. Present in the environment at all times, without interruptions. Classic examples are the salinity of the World Ocean or the basic gas composition of the atmosphere. Evolutionarily, living beings have developed stable adjustments to them, which are called adaptations.
- Periodic. Manifest with a certain, predictable periodicity. These can be daily, seasonal, annual fluctuations, or cycles tied to the lunar month. Specific adaptations to such cyclical changes are called biological rhythms.
- Non-periodic. Arise spontaneously and suddenly, not being the norm for specific environmental conditions. Their main feature is that organisms have no pre-formed adaptations to them whatsoever.
Relationship with population density
An important ecological criterion is whether the strength of the factor's impact depends on the number of individuals living in a given territory.
Density-independent factors This category includes natural disasters (floods, severe fires, devastating earthquakes) and most climatic phenomena. In such situations, the percentage of surviving or dead individuals is in no way related to how high the initial population density was before the catastrophe.
Density-dependent factors This includes the overwhelming majority of biotic interactions. The higher the population density, the stronger organisms influence each other (e.g., due to resource scarcity). This group also includes certain abiotic environmental changes if they are provoked by the vital activity of the organisms themselves under conditions of high crowding.
Briefly: answers to topical questions
What forms of biotic interactions are distinguished between species in a biocenosis?
Interspecific biotic interactions in a biocenosis are classified according to the effect of species on each other:
- Neutralism (0/0) — species do not directly affect each other.
- Commensalism (+/0) — one species benefits, while the interaction is indifferent to the other.
- Cooperation (+/+) — both species benefit; the interaction is not obligatory for their existence.
- Mutualism (+/+) — the interaction is beneficial for both species and obligatory for their existence.
- Amensalism (0/-) — one species unilaterally suppresses the other without experiencing any effect itself.
- Competition (-/-) — both species mutually suppress each other.
- «Prey — exploiter» relationships (+/-) — predator — prey, herbivore — plant, parasite — host.
What types of anthropogenic factors are distinguished by their nature of impact on the environment?
According to their nature of impact on the environment, anthropogenic factors are subdivided into physical, chemical, and biological alterations.
Anthropogenic pollution exerts two types of influence on living organisms:
- Direct influence — caused by olfactory (effect on olfactory receptors) and resorptive (absorption into the bloodstream) actions of pollutants.
- Indirect influence — associated with the retention or scattering of visible and ultraviolet rays by a polluted atmosphere.
Negative anthropogenic impacts also include the rapid depletion of underground deposits, alteration of riverbeds, and creation of artificial reservoirs, leading to the flooding of lands.
What are the main laws of action of ecological factors on an organism?
The action of ecological factors on an organism is subject to regularities associated with the optimum, tolerance, and limiting factor.
Three zones of impact are distinguished:
- Zone of optimum — the range of factor action most favorable for the vital activity of the organism.
- Zone of depression (peessimum, stress) — deviation from the optimum at which vital activity is hindered or depressed, but possible.
- Zone of death — conditions under which vital activity becomes impossible and death occurs.
Also distinguished are limits of tolerance: the lower and upper limits of factor values compatible with life. The interval between them is called the tolerance range.
Limiting factor — a factor whose value deviates most from the optimum or is closest to the limits of tolerance and limits the survival or prosperity of the organism.
The origin of factors is easy to remember by the acronym ABA: Abiotic (non-living nature), Biotic (living organisms), Anthropogenic (human intervention).
Class and exam questions
Do organisms have adaptations to non-periodic factors?
No. Since such factors arise suddenly and do not occur under normal environmental conditions, evolutionary adaptations to them cannot develop.
What are biological rhythms in the context of ecology?
This is a special type of adaptation that forms in response to the action of periodic factors having strict cyclicity (daily, seasonal, or annual).
Does mortality during a flood depend on population density?
No, it does not depend. A flood is a natural disaster belonging to density-independent factors, so the proportion of dead individuals is not determined by their initial number in the area.
What else to study on this topic
- Types of intraspecific interactions in populations
- Forms of interspecific contacts (symbiosis, competition, predation)
- Mechanisms of biological rhythm formation
- Chemical abiotic factors and their effect on hydrobionts
- Anthropogenic transformation of ecosystems
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