Allee effect

BIOMATHS
ALLEE EFFECT

1. BSC. (H) BIOTECHNOLOGY SEMETER- V subject: biomathematics presentation topic: ALLEE EFFECT Presented by: Joydeep pal (BWU/BBT/18/036) Aakanksha krishna (BWU/BBT/18/041 )

2. History Allee effect described by Warder Clyde Allee (1885-1955).

3. Population regulation Two types: 1. Density dependent; 2. Density independent 1. Density dependent: populations, birth rate and death rate do not change with population density. Factors : Birth rate, death rate, nutrition… 2. Density independent: Population, birth rates fall but the death rate rise. Factors (environmental): Flood, earthquake…. For example: Population increasing means birth rate also increasing but date rate also rising – Positive feedback (which is called Allee effect). If Birth rate decreasing and death rate increasing with the density– Negative feedback.

4. What is allee effect? The  Allee effect  is a phenomenon in biology characterized by a correlation between population size or density and the mean individual fitness (often measured as per capita growth rate ) of a population or species. The generally accepted definition of Allee effect is positive density dependence, or the positive correlation between population density and individual fitness.  It is sometimes referred to as "undercrowding" and it is analogous to “depensation" in the field of  fishery sciences .

5. STRONG ALLEE VS WEAK ALLEE EFFECT

6. Mechanism Due to its definition as the positive correlation between population density and average fitness, the mechanisms for which an Allee effect arises are therefore inherently tied to survival and reproduction. In general, these Allee effect mechanisms arise from cooperation or facilitation among individuals in the species. Examples of such cooperative behaviors include better mate finding, environmental conditioning, and group defense against predators.

7. MATHEMATICAL EXPRESSION As a result of Allee’s work , a population where the per capita growth rate declines at low population size is said to show an Allee effect. One of the simplest mathematical models, a variation of the logistic equation is: dN /dt= rN (1-N/K) (N/A-1) Where, A is called the Allee threshold. The value of N(t) A is the population size below which the population growth rate becomes negative due to allee effect. N= population size; K= carrying capacity; r = intrinsic rate of increase .

8. Examples Of Allee Effect In Various Taxa Fruit flies are considered to be one of the most dangerous pests in agriculture as they have the potential to attack approximately 400 crops globally. Usage of sterile males is one of the techniques used to control them which creates Allee effect. It is important in schooling fishes which are group living animals. If harvesting pressure is high, it may cause a potential population disintegration.

9. ACKNOWLEDGEMENT I would like to thank our respected HOD sir and I also thankful to Souvik Sinha sir to give this opportunity to present in this interesting topic.