Characteristic signs of regression
The transition of a systematic group into a state of biological regression can be recognized by a number of clear criteria indicating a decline in its evolutionary success:
- Population decrease: the number of individuals in a population or group is steadily declining.
- Changes in the range: there is a narrowing of the original habitat or its fragmentation (breakup into isolated areas).
- Elimination: a massive, often catastrophic death of organisms is observed.
- Final stage: the process can predictably culminate in the complete extinction of a specific group.
Examples of groups in a state of regression
The decline in the level of adaptation can be observed at completely different levels of organization of living matter—from plants to humans. Classic examples include:
- Plant kingdom: certain species of ferns.
- Animal kingdom: the vast majority of modern amphibians and reptiles.
- Human population: if humans are considered exclusively as a biological species, small indigenous peoples may exhibit signs of regression.
Extinction and its types
The final point of biological regression is extinction. This evolutionary process is traditionally divided into two main types:
- True extinction. Represents the absolute physical death of all age groups without exception belonging to a given systematic taxon.
- Pseudo-extinction. Occurs within the framework of phyletic evolution. In this case, the systematic group does not disappear without a trace, but smoothly transforms into a completely new taxon.
Probability and factors of extinction
The duration of existence of an individual species varies widely (from 200,000 to several million years). The risk of a species disappearing is subject to strict patterns and depends on the characteristics of the group itself:
Directly proportional relationship (the higher the indicator, the higher the risk):
- Body size of the organism.
- Occupied trophic level in the food chain.
Inversely proportional relationship (the higher the indicator, the lower the risk):
- Total number of individuals in the group.
- Area of the occupied habitat range.
Briefly: answers to topical questions
Why does a higher trophic level in the food chain increase the risk of species extinction?
The probability of species extinction is directly proportional to the trophic level it occupies.
At the same time, energy in ecosystems does not circulate, but flows in one direction and dissipates as heat. According to the 10% rule (Lindeman's efficiency), on average only about 10% of energy is transferred from one trophic level to another. Therefore, by the end of the food chain, energy runs out, and the length of food chains is usually limited to 3–5 links.
The rule "Large predators are vulnerable, small packs are stable" will help remember the risk factors for extinction. The risk increases with body size and trophic level (direct proportion), but decreases if there are many individuals and the range is broad (inverse proportion).
Class and exam questions
What is the essence of biological regression?
The essence lies in a global decrease in the level of adaptation of organisms to their environmental conditions.
What does the term "pseudo-extinction" mean?
This is a process in which the original systematic group does not completely perish, but turns into another taxon as a result of phyletic evolution.
How does body size affect the probability of extinction?
The probability of extinction is directly proportional to body size: the larger the organism, the higher the risk of species disappearance.
Which vertebrate classes are currently experiencing regression?
According to the materials, the majority of amphibian and reptile species are currently in a state of regression.
What else to study on this topic
- Mechanisms of narrowing and fragmentation of the habitat range
- Causes of massive catastrophic species elimination
- Phyletic evolution as the basis of pseudo-extinction
- The relationship between the trophic level and the probability of taxon extinction
- Data and criteria of the International Union for Conservation of Nature (IUCN)
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