ECOLOGY

by Purwaning Rohmah/BIO off A 2015 UM

MODEL OF POPULATION GROWTH

There are two simplest models of population growth use deterministic equations (equations that do not account for random events) to describe the rate of change in the size of a population over the time. These models are exponential groth and logistic growth.

1. Exponential Growth

Exponential growth describes theoretical populations that increase in numbers without any limits to their growth. Bacteria grown in the lab provide an excellent example of exponential growth. If 1000 bacteria are placed in a large flask with an abundant supply of nutrients (so the nutrients will not become quickly depleted), the number of bacteria will have doubled from 1000 to 2000 after just an hour. In another hour, each of the 2000 bacteria will divide, producing 4000 bacteria. After the third hour, there should be 8000 bacteria in the flask. These example of bacteria growth in a flask is not truly representative of the real world where resources are usually limited.

The key concept of exponential growth is that the population growth rate —the number of organisms added  in each generation—increases as the population gets larger due to no limits that affects their growth.

 

2. Logistic Growth

However, when a species is introduced into a new habitat that it finds suitable, it may show exponential growth for a while. Exponential growth may happen for a while, if there are few individuals and many resources. But when the number of individuals gets large enough, resources start to get used up, slowing the growth rate. Eventually, the growth rate will plateau, or level off, making an S-shaped curve which is called as logistic growth. The population size at which it levels off, which represents the maximum population size a particular environment can support, is called the carrying capacity, or KKKK.