Organisms and Population Test - 6

Mortality and emigration would necessarily decrease the density of a population in a given habitat.

Biotic potential is defined as the physiological capacity of organisms to produce their offspring under natural conditions. It is also called reproductive potential. In nature, the biotic potential of organisms is enormous but all the organisms do not survive due to the lack of food and space. There are also a number of diseases and the predatory organisms, that feed upon other organisms. The carrying capacity is the maximum number of individuals which the environment can support or sustain.

Current human population growth appears to be J-shaped as we have either not yet met our population carrying capacity, or have exceeded the carrying capacity, but have not yet seen the population crash normally associated with J-shaped or exponential population growth. If the human population meets the carrying capacity it will closely resemble an S-shaped population curve.

Natality in population ecology is the scientific term for birth rate. Along with mortality rate, natality rate is used to calculate the dynamics of a population. They are the key factors in determining whether a population is increasing, decreasing or staying the same in size. Natality is the greatest influence on a population’s increase. Natality is shown as a crude birth rate or specific birth rate. Crude birth rate is used when calculating population size (number of births per 1000 population/year), whereas specific birth rate is used relative to a specific criterion such as age. By calculating specific birth rate, the results are seen in an age-specific schedule of births.

Formula = the rate of change in population size) = (the contribution of each individual to population growth) x (the number of individuals in the population

Population growth curve is of two types - Exponential and logistic growth. Logistic growth curve represents the population growth at present.When resources are limited then population exhibit logistic growth curve. It is sigmoid or S shaped indicating that population density of an organism increases at a fast rate initially. It hits a maturity phase where growth slows down and then stops.

Population growth is defined as an increase in the size of a population over a specific time period. The growth rate is calculated using two factors – the number of people and the unit of time.
The size of the population does not rise indefinitely because of the limitation of certain factors. These factors are environmental stress, water and nutrients, space and light as well as the existence of competitors.

Demography is the study of human populations – their size, composition and distribution across space – and the process through which populations change. Births, deaths and migration are the 'big three' of demography, jointly producing population stability or change.

The genetic drift is a drastic change in allele frequency when population size is very small. Its effects are more marked in a small isolated population.

Correct option is D

The rate of growth or decline of a population basically depends on four factors, including natality rate or births, mortality rates or death, and the emigration and immigration rates. These four factors affect the inflow and outflow of a population and hence, affects the growth and decline of a population.

So, the correct answer is 'All of these'

In most systems, the initial growth is slow (lag phase), and it increases rapidly thereafter,  at an exponential rate (log or exponential phase). Here, both the progeny cells following mitotic cell division retain the ability to divide and continue to do so. However, with limited nutrient supply, the growth slows down leading to a stationary phase. If we plot the parameter of growth against time, we get a typical sigmoid or S-curve. A sigmoid curve is a characteristic of living organism growing in a natural environment. It is typical for all cells, tissues and organs of a plant.

Thus, the correct answer is option B.

Exponential model is the one in which rate of change in anything is directly proportional to the number of the thing present. Exponential phase shows the exponential growth. Thus the size or the number increases at a constant growing rate.

S-shaped growth curve (sigmoid growth curve) A pattern of growth in which, in a new environment, the population density of an organism increases slowly initially, in a positive acceleration phase; then increases rapidly approaching an exponential growth rate as in the J-shaped curve; but then declines in a negative acceleration phase until at zero growth rate the population stabilizes.

Adaptations may be morphological involving shape, size and external features of the living organisms or anatomical including adaptive modifications in the visceral organs. These adaptations are mostly due to the effect of environment (both a biotic and biotic) in which the organisms reside. Based upon the habits and habitats met within the present organisms, Mathew has classified adaptations into the following categories.

(i) Cursorial adaptations or speed adaptations for running.

(ii) Fossorial adaptations or adaptations for burrowing.

(iii) Scansorial (arboreal) adaptations or adaptations for climbing.

(iv) Volent adaptations or adaptations for flight.

(v) Cave adaptations

(vi) Desert adaptations

(vii) Aquatic adaptations.

The density of a population in a given habitat during a given period changes due to changes in four basic processes, two of which (natality and immigration) contribute to an increase in population density and two (mortality and emigration) to a decrease. In a zero population growth density natality is balanced by mortality.