Exponential Growth vs Logistic Growth
Population growth is the change in a population size over a certain time period. Population growth rate is the change in the number of individuals per unit time. This rate is basically determined by the birth rate (rate at which new individuals are added to the population), and the death rate (rate at which individuals leave the population). Population size never increases indefinitely due the limitation of resources such as light, water, space, and nutrients and the presence of competitors. The population growth can be explained by two simple growth models; exponential growth and logistic growth.
Exponential Growth
Exponential growth is defined as the population growth in which the number of individuals accelerate rapidly even when the rate of increase remains constant, finally resulting a population explosion. Here, the birth rate of a particular population alone determines its growth rate. Resource availability is the limiting factor for this growth. When we plot the number of individuals against time, the result will be a J-shaped characteristic curve for exponential growth. According to the curve, the growth starts slowly and then accelerates as the population size increases. In real populations, both food and space become limited as the population become crowded. Therefore, this model is more idealistic, unlike the logistic growth model and sometimes applies for bacterial cultures that have unlimited resources.
Logistic Growth
Logistic growth involves exponential population growth followed by a constant or steady state growth rate. When a population reaches its carrying capacity, its rate growth slows greatly due to the limiting availability of resources for each new individual. The carrying capacity is the size, in which a population ultimately gets stabilized. At this time, the growth rate of that population fluctuates slightly above and below the carrying capacity. This model is more realistic and can be applied for many population exist on earth.
What is the difference between Exponential Growth and Logistic Growth?
• Characteristic curve for exponential growth results in a J-shaped growth curve, while logistic growth results in a sigmoid or S-shaped growth curve.
• Logistic growth model applies to a population that approaches its carrying capacity, while exponential growth model applies to a population that has no growth limit.
• Logistic growth ends up with slightly constant population growth rate (when the population growth rate reaches its carrying capacity), whereas exponential growth ends up with the population explosion.
• Logistic growth can be seen in many population, and it is more realistic than exponential growth. Exponential growth is better suited for bacterial cultures that have unlimited resources such as space and food.
• There is no upper limit for exponential growth model, whereas carrying capacity of a population is the upper limit of logistic growth model.