Saved Bookmarks
| 1. |
Question : What is meant by growth models ? |
|
Answer» Solution :• Growth model shows the specific and predictable pattern of growth of population with TIME. • Growth of population takes place according to availability of food, habit condition and presence of other BIOTIC and abiotic factors. • There are two main types of models: • (a) Exponential Growth: This kind of growth occurs when food and space is available in sufficient amount. • When resources in the habitat are unlimited, each species has the ability to realise fully its innate potential to grow in number . • The population grows in an exponential or geometric fashion. • If in a population of size N, the birth rates as REPRESENTED as .b. and death rate as .d.. • Then increase and decrease in N during unit period time .t. will be `dN//dt = (b - d) xx N` Let `(b - d) = r`, then `dN//dt = rN`.  • Then, the r in this equation is called .intrinsic rate of natural increase. and is a very important parameter chosen for assessing impacts of any biotic or abiotic factor on population growth. • To give some idea about the magnitude of r values, for the Norway rat the r is 0.015, and for the flour beetle it is 0.12. • In 1981, the r value for human population in India was 0.0205. • The above equation describes the exponential or geometric growth pattern of a population and results in a J-shaped curve when we plot N in relation to time. • If you are familiar with basic calculus, you can derive the INTEGRAL form of the exponential growth equation as `N_t= N_0 e^(rt)` where `N_t` = Population density after time t `N_0` = Population density at time zero r = intrinsic rate of natural increase e = the base of natural logarithms (2.71828) • Any species growing exponentially under unlimited resource conditions can reach enormous population DENSITIES in a short time. • Darwin showed how even a slow growing animal like elephant could reach enormous numbers in the absence of checks. |
|