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Allee Effect Overview
Allee effect is defined as the process which explains how the size of a population affects its chances of survival. The term was coined first by the scientist Warder Allee. He described this term in the early 20th century.
Allee effect is important to understand as it makes us aware of why some species struggle to survive if their populations are very small. When a region’s population is extremely low and stays low, it has a powerful Allee effect. When the population is small but still growing positively, even if slowly, the Allee effect is weak.
Let us break down the concept of allee effect in detail going further in the blog. Before that, we shall discuss important terms related to it.
What Is Population?
Population in biological terms refers to a group of species living in the same area. A colony of penguins on an island or a gang of lions in a savannah are two examples of populations.
When species reproduce and add new members, populations increase. They get smaller when species die or run out of food or partners.
The size or density of a population is necessary for a powerful Allee effect population. The population will begin to decline rather than increase if it drops below this level.
In contrast, a population with a modest Allee effect increases positively even at small sizes, however more slowly. The population may die extinct if it falls below the critical threshold in a strong Allee effect.
What was the Observation Of Allee on the Basis Of Aggression?
According to Alley’s observation aggression had a positive effect on land isopods.
- Their survival rate had a negative effect when they were isolated.
- The land isopods desiccated rapidly when isolated.
- His practical demonstrations of the advantages of cooperative groupings defied both the Malthusian theory and the logistic model.
Taking into account both kinds of Allee effects, the broad concept that follows is mentioned below:
A positive correlation between population growth over time and individual survival rates is known as the Allee effect.
A critical population size may be reached by this relationship. Below this point, the population may not be able to live.
What is the Allee Effect?
The Alley effect shows us how small populations find it difficult to survive as compared to the larger ones. There are many reasons why small populations find it difficult to survive against the larger ones. Mentioned below are the factors that impact their survival.
- Difficulty finding mates – In a small population, individual species are scattered which makes it difficult to find their mates. Hence, reproduction is not possible frequently and is very rare.
- Less protection – In larger groups of species, individuals protect each other. In a small community, there aren’t enough individuals to provide protection, making it easier for predators to attack.
- Inbreeding – In tiny populations, individuals may choose to mate with species members. This term is also called inbreeding. It may result in genetic issues, which can weaken the population and make it less likely to survive.
What Are The Types Of Allee Effect?
The Allee effect is of two types mainly. It comprises strong and weak Allee effects. Mentioned below are these effects in brief.
Strong Allee Effect
- In very tiny populations, the Allee effect is powerful.
- In this instance, the population cannot rebound if it falls below a particular size.
- Individuals have trouble finding partners and reproducing.
- The rate of population increase starts to decline.
- Examples – African wild dogs and passenger pigeons.
Weak Allee Effect
- A small but rising population is said to have a modest Allee effect.
- Although it is slower than in larger populations, the growth rate is still positive.
- Species still have difficulties, yet the population does not go extinct right away.
- With smaller sizes, the growth rate declines but stays positive.
- Examples – some pollinating bees and rare flowering plants.
What Are The Examples Of The Allee Effect in Various Taxis?
The Allee effect varies with different different groups of living organisms. Here are the examples of the Allee effect across various taxa.
Fish
- For breeding, Atlantic cod fish require large populations.
- There is a strong Allee effect in small groups.
- It becomes harder for individuals to find partners.
- This slows down reproduction.
- As a result, the population decreases.
Fruit flies
- Fruit flies can affect almost 400 crops worldwide.
- They are regarded as one of the most hazardous agricultural pests.
- One method of control that produces the Allee effect is the employment of infertile males.
- Large-scale releases of natural enemies are made to ensure that the Allee effect is avoided.
Pollinating bees
- Some bee species need large populations to pollinate flowers well.
- In a small population, there are fewer bees.
- This makes pollination less effective.
- Reduced pollination leads to fewer plants reproducing.
- In turn, there is less food for the bees.
- This is a weak Allee effect because the population grows slowly.
Passenger pigeons
- In the past, passenger pigeons were widespread throughout North America.
- Overhunting caused a reduction in their population.
- Allee was strongly impacted by this.
- It becomes tougher for the pigeons to find partners when there are fewer of them.
- This ultimately caused them to go extinct.
FAQs on Allee Effect
What is the Allee Effect?
Allee effect is defined as the process which explains how the size of a population affects its chances of survival. Allee effect is important to understand as it makes us aware of why some species struggle to survive if their populations are very small. A positive correlation between population growth over time and individual survival rates is known as the Allee effect.
What are the two main types of the Allee Effect?
The Allee effect is of two types mainly. It comprises strong and weak Allee effects. In case of strong allee effect population is very small. It cannot grow because individuals have difficulty finding mates. If the population drops below a certain size, it risks extinction.When a population is small but still growing, though slowly. Growth rates are positive but decrease as the population size gets smaller.
What are the Factors that Contribute to the Allee Effect?
Several factors affect the Allee effect. One contributing aspect in small populations is the challenge of finding partners. The fact that small groups are less protected from predators is another consideration. Limited interaction among individuals is another factor. In tiny populations, inbreeding can also occur. This further depletes the population and causes genetic issues.
What is null hypothesis?
An other term associated with population expansion is the null hypothesis. It explains a scenario in which growth rates are both positive and declining.
What is the difference between the Allee Effect and density dependence?
Density dependence describes how population growth is influenced by population size, both high and low, while the Allee Effect concentrates on the difficulties small populations encounter.
