Exponential growth means growth in the population of organism at a constant rate per unit of time. It is called exponential growth because existing population is multiplied in geometrical ratio.
The geometric pattern of increase is 2.4,8,16 and so on. By contrast, a pattern of growth that increases at a constant amount per unit of time is called arithmetic growth. The sequence in this case might be 1,2,3,4 or 1,3,5,7. In figure 7.2 placed below which reflect both Geometric and Arithmetic growth.
In India we usually talk about population growth of human beings. Population also increases of animals and other organisms too. In overseas countries attention is also paid to changes in the population on organisms.
The moose population as well as other organisms has the ability to grow exponentially. In which reflects growth of moose and wolf populations on Isle Royal National Park from 1900-1995 moose first appeared on the island shortly after 1900. By 1929, the moose population had grown to about 5000 and had exhausted the easily available food supply. A catastrophic die-back occurred during the 1930s, when 97 percent moose died. The appearance of wolves after 1940 at first reduced the moose population but then established a dynamic equilibrium around what appears to be the carrying capacity.
Reasons for exponential growth:
The main reasons with regard to the growth of population (moose population and other organisms) with given appropriate environment are as follow:
Experience of biologists reveals that each cow moose reaches sexual maturity at the age of three or four. If she remains healthy and has enough eat and survive it can produce one to three calves each year for the next eight to ten year.
This means that each female moose can produce as many as 30 calves during her life time. If half of those calves are female then the population will increase at a 14 to 35 percent annual growth rate.
In you will come to know that the number of moose added to the population at the beginning of the growth curves rather small. But within a very short time, the numbers began to increase.
The growth curve produced by this constant rate of unfettered (not like iron bar) growth is called a J curve because of its shape. Moose population growing at 35 percent doubles every two year. You can also apply this rate to calculate doubling time of human population. Countries growing at 4 percent per year will double their populations in 17.5 years.
Biotic potential means maximum reproductive rate of on organism. There are many other organisms which have faster reproducing capacity compared to moose and humans. Housefly has fastest reproductive rate. Each female fly lays an average of 120 eggs in each generation.
The eggs hatch and mature into sexually active results and lay their own eggs in fifty six days. In one year if its entire offspring survived long enough to reproduce, a single female could be the ancestor of 5-6 trillion flies. The result is outstanding. This example clearly illustrates the potential for biological population to increase rapidly.