Allee Effect

May 08, 2023, 16:45 IST

The Allee effect is a biological phenomenon that explains a correlation between the size of the population and the mean of individual fitness.

It is a density-dependent phenomenon that generally occurs in sparsely dense areas.

Allele can be defined as an alternative part of a gene that might produce distinguishing phenotypic features in organisms.

The Allee effect generally occurs at low population density and becomes more common in places that are under the direct effect of climate change.

Strong and Weak Allee Effect

A region will have a strong Allee effect in which the population shifts to the critical point or in other words where the population growth is negative. When the size of the population goes below the threshold rate, it is destined to extinct.

Whereas, a weak allee effect occurs when the proliferation rates are high and there will always be a positive per capita growth rate.

Component vs. Demographic Allee Effects

The component Allee effect is demonstrated by the population when there is a positive correlation between the fitness component and the population size.

Whereas, in demographic Allee effect is the direct effect of component allee when it makes a positive correlation between per capita population growth and the size of the population. So, it says that the demographic Allee effect must show at least one component Allee effect. In contrast, the component Allee effect is independent of the presence of the demographic allee effect.

• Mechanisms

The mechanism of the allee effect is directly dependent on survival and reproduction. This allee effect arises from various cooperative behaviors by the population such as mating, group defense, conditioning by the environment, and cooperative feeding.

All of this behavior is well observed in the field which is why the allee effect is associated with it.

• Ecological Mechanism

It is directly related to environmental factors such as mate limitation, and cooperative defense.

Mate Limitation - it is the difficulty experienced in finding a suitable and compatible male partner for mating, especially at the time of low population density times.

This problem generally arises in animals that have limited mobility such as zooplankton, and sessile invertebrates. If we talk about plants, those plants which are pollinated by wind face this problem due to the low likelihood of successful pollination by the wind in sparse regions.

• Cooperative Defense

It is the act of protecting ourselves from predators and other danger-like situations by showing group anti-predator behavior.

It means higher vigilance is exhibited by the people living in larger groups, so less time and energy is wasted.

But in smaller groups, due to low vigilance, a large amount of energy is contributed, reducing the fitness of an individual. Some fishes move together in large groups such as schools of sardines fish, which confuses and prevents predators to attack them.

• Environmental Conditioning

It is the phenomenon by which the individuals of the population work together in order to improve the immediate environment for the better experience of the future generation.

It results in various changes in the biotic and abiotic factors of the environment.

Human-Induced

Human-made practices generally result in the exploitation of naturally existing species. When rare species are more desirable than other common species, the prices go up. This phenomenon is generally called the “anthropogenic allee effect”. Of this, the rare species which were more desirable go extinct leaving behind the other common variant of species.

This concept of the anthropogenic allee effect is used as a most common thing to determine the danger to the rare species because of the economic market.

Genetic Mechanisms

Genetic diversity means the presence of a large variety of species in a given population. When there is a decrease in the population, genetic diversity automatically decreases. Under such a situation, an allee effect is observed.

Therefore, the fitness of the population also decreases.

Examples of Allee Effect

There are certain examples that show the Allee effect:

• Fruit flies are known for their capacity to degrade agricultural fields, as it acts as a pest that spoils the field. To counter this effect, the use of sterile males can be helpful to control them which thereby causes an allee effect. In addition to this, a large number of enemy flies are released which counter the fruit flies and their bad effects on the farm.
• When the population density is low, it causes the extinction of species due to the absence of partners to mate with.

The Allee effect can reduce the speedy growth of the population and can help in preventing biological invasions.

Conclusion

So we can say that the allee effect has a direct influence on the population with a positive association with the fitness of the individuals and the population density. It can drive the extinction of small species groups and can really influence population statistics.

Frequently Asked Questions (FAQs)

Q1. Can the Allee effect lead to the extinction of species?

Ans. The Allee effect is increased when the number of individuals decreases in a population, thus increasing the allee effect. Thereby, reducing the chances of mating and reproducing young ones, which ultimately leads to the extinction of species.

Q2. What are some factors which directly influence population distribution?

Ans. Factors such as the topography of the area, climate, landforms, soil, and mineral resources, natural harbors, rivers, and canals are all such factors that influence the population distribution

Q3. What are the issues caused by an increasing population?

Ans. Problems such as ecological degradation, increase in conflicts, and risk of disasters may arise.

Q4. What is the difference between a gene and an allele?

Ans. A gene is the smallest unit of heredity information which is made up of DNA and carries all the genetic information of a human.

Whereas, an allele is a variant of a gene in which the two copies are different from each other. Allele represents themselves by differing in phenotype.