Biotic potential, population growth curves

Biotic potential

The biotic potential is the maximum reproductive capacity of the population if the resources are unlimited. But according to the biotic potential organism are not able because of the restriction by the environmental potential or any condition that inhibits the increase in the number of the population. The biotic potential is only reached when the environmental conditions are favourable. The species reaching the biotic potential would exhibit exponential potential growth and is said to have the high fertility rate.

It is the highest possible vital index of the specie with the:

1.Reproductive potential

It is the upper limit to the biotic potential.

2.Survival potential

As the reproductive potential does not account for the number of the gametes surviving , the survival potential is a necessary component of the biotic potential and is the reciprocal of the mortality. In the absence of the mortality, biotic potential = reproductive potential.

In this Chapman has identified the two components

Nutritive potential – the ability to acquire and utilize food for growth and energy.

Protective potential – potential ability of the organism to protect itself against the dynamic forces of the environment assuring the successful fertilization (mating) and caring for the young.

Population Dynamics

The population dynamics in the branch of the life science that studies about the short-term and the long-term changes in the size and the age composition of the population and the biological and the environmental processes influencing those changes. The population deals with the way the population is affected by the birth and the death rates by the immigration and the emigration and the studies topics such as ageing population and the population decline.

Population growth and the growth curves

The population is not static . Over each and every moment in the world, the population size differs. The growth is one of the dynamic features of the population size increase. When the number of the individuals of the species plotted on the y- axis and time on the x- axis a curve is obtained that indicates the trend in the growth of the population size in the given area. Therefore the obtained curve of the population through the time is known as the population curve. There are two types of the curve

a. S- Shaped curve or the logistic curve or the sigmoid curve.

b. J- shaped curve or the geometric curve

a. S- shaped growth curve

In the S- shaped curve the initial growth is slow and is known as lag and then occurs the positive acceleration phase. This is followed by the rapid growth continuous up to certain point after which there is the steady decrease in the growth taken as negative form. The level in which no major occurs occur is known as saturation level or the carrying capacity. The saturation point shows that there is the almost equal number of organisms taking birth and dying so that the equilibrium is established between natality and the environment resistance and maintaining a maximum number of the population density for the longer period . The curve results from the sigmoid form.

The sigmoid curve of the growth rate is common in population ecology. The S- shaped growth curve can be represented by:

dN/dt = r. N (K-N)/ K

where

dN/ dt = rate of population growth per unit time

N = starting population

K = maximum population size ( constant) or carrying capacity of the environment)

r = Rate of increase ( intrinsic rate of increase)

b. J- shaped growth curve or J- shaped growth curve

The J- shaped growth curve involve the geometric ratio of the increase up to a certain point after which there is a sudden growth in the population. The change in the environmental factors makes the sudden change in the population. The more increase in the population also causes the decline in the food materials and also the habitat that alternately results in the decrease in the population size. The growth curve obtained in this progression is more or less J- shaped. This type of growth is not common in nature but found when the favourable condition meets the individual species needs.

The growth is given by the equation

dN/ dt = r. N

where,

dN = rate of the population growth

dt = time interval

r = rate of geometric change

N = population size

The integral population is

N_t = N._e^r.t

This equation is widely used for the calculating growth

where

Nt = number of the individuals at time t

r = intrinsic rate

t = time taken

Opportunistic or The r- selected species

Every individual has the maximum reproducing capacity and has a characteristics mode of reproduction. At the one extreme, one species reproduce early and put most of their energy into the reproduction. they have

Many offspring's each time they reproduced.

Reach reproductive age rapidly.

Have short generation time.

Give their offspring's little or no time for the parental care or the protection to help them to the survival.

Short lived with a lifespan of less than a year.

The species with such a capacity for the higher intrinsic rate of increase (r) are called r- selected species. E.g algae, bacteria, rodents, annual plants such as dandelion and most of the insects. These species tend to be opportunistic and they reproduce rapidly under the favourable condition, even in the disturbed environment but the competition among the opportunists makes more or less unfavourable condition. Therefore mostly r- selected species go through the irregular unstable boom cycles of the growth in their population growth. To survive opportunists must continually invade new areas to compensate for being displaced by the more competitive species.

Competitive or K- related species

These species

Put fairly little energy in the reproduction.

Tend to produce late in the life.

Have a few offsprings with the long generation time.

Are cared for or protected by one or both the parents until they reach the reproductive age.

The result creates little individual competition for the resources and reproduces a few young to begin the cycle again. Such species are called k- selected species because they tend to do well in the competitive condition when their population size is near the carrying capacity of the environment. These follow logistic population growth. Examples are:

Most large mammals such as elephant, whale , human etc.

Birds, prey animal etc.

Large plant such as oak trees, cactus, redwood trees and most of the tropical forest.

The k- selected species with the long generation time posses the low reproductive rate such as elephant, rhinoceros, shark etc. So in the general practice ethe k- selected species forms the best eco- system in the agriculture. The r- selected species experienced the habitat, forest, grassland and the raising crop. The concept of the carrying capacity is based on the environmental resistance which consists all the factors affecting to the limit the growth of the population in a given space and the time determined by the biotic potential . Therefore together the biotic potential and the environmental resistance determines the carrying capacity. The number of the individuals of a species can be sustained in the given environment.

References

Santra, S. (2004). Environmental Science . India: New Central Book Agency (p) Ltd.

T., R. (2008). Towards a Sustainable Future . India: PHI (p)Limited.