Practice Corner MCQ

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(c)

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(a) : Total number of plants (in the beginning) \(=30\)

New plants added by reproduction \(=25\)
Birth rate (of a population)

\(
=\frac{\text { New plants }}{\text { Total number of plants }}=\frac{25}{30}
\)

\(=0.83\) individuals per lotus per year
Number of plants died \(=8\)
Death rate (of a population) \(=\frac{\text { Number of deaths }}{\text { Total number of plants }}\)
\(=\frac{8}{30}=0.26\) individuals per lotus per year.

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(d): The age structure of a population is the percentage of individuals of different ages such as young, adult and old. Age structure is shown by organisms in which individuals of more than one generation co-exist. Birth rate, death rate and generation time are important parameters related to it.

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\(
\begin{aligned}
&\begin{aligned}
& \text { (a) : Death rate }=\frac{\text { Number of deaths }}{\text { Initial number of individuals }} \\
& =\frac{200}{800}=\frac{1}{4}=0.25
\end{aligned}\\
&\text { (a) : Death rate }=\frac{\text { Number of deaths }}{\text { Initial number of individuals }}\\
&=\frac{200}{800}=\frac{1}{4}=0.25
\end{aligned}
\)

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(a) : Age distribution is percentage of individuals of a given age or age group. A population at any given time is composed of individuals of different ages. If age distribution is plotted for the population, the resulting structure is called age pyramid.

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(c) : Age distribution is percentage of individuals of a given age or age group. A population at any given time is composed of individuals of different ages. If age distribution is plotted for the population, the resulting structure is called age pyramid.

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(c) : Triangular age pyramid has high proportion of prereproductive individuals, moderate number of reproductive individuals and fewer post-reproductive individuals. It represents young or rapidly growing population.
In urn-shaped age pyramid, the number of reproductive individuals is higher than the number of pre-reproductive individuals. It represents declining or diminishing population with negative growth. In bell-shaped age pyramid, the number of pre-reproductive and reproductive individuals is almost equal. Post reproductive individuals are comparatively fewer. It represents stable or stationary population, neither growing nor diminishing.

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(a) : Age distribution is percentage of individuals of a given age or age group. A population at any given time is composed of individuals of different ages. If age distribution is plotted for the population, the resulting structure is called age pyramid.

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(b) : Different age groups have different reproductive capabilities. Pre-reproductive individuals are the young individuals which will enter the reproductive age after some time. They are the potential source of increase in population. Reproductive individuals are the ones which are actually adding new members to the population. Post-reproductive individuals are older individuals which no longer take part in reproduction.

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(a) : Different age groups have different reproductive capabilities. Pre-reproductive individuals are the young individuals which will enter the reproductive age after some time. They are the potential source of increase in population. Reproductive individuals are the ones which are actually adding new members to the population. Post-reproductive individuals are older individuals which no longer take part in reproduction.

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(c) : A population with large number of older individuals than younger ones is likely to decline since older individuals do not take part in reproduction.

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(c) : Triangular age pyramid has high proportion of prereproductive individuals, moderate number of reproductiveindividuals and fewer post-reproductive individuals. It represents young or rapidly growing population.
In urn-shaped age pyramid, the number of reproductive individuals is higher than the number of pre-reproductive individuals. It represents declining or diminishing population with negative growth. In bell-shaped age pyramid, the number of pre-reproductive and reproductive individuals is almost equal. Post reproductive individuals are comparatively fewer. It represents stable or stationary population, neither growing nor diminishing.

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(b) : Population density is the number of individuals present per unit area or volume at a given time. If the total number of individuals is represented by letter N and the number of units of space (area for land organisms and volume for water organisms) by letter \(S\), then the population density \(D\) can be represented as \(D=\) N/S. For instance, number of animals per square kilometre, number of trees per acre in a forest, etc.

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(d)

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(c) : Sometimes, for certain ecological investigations, there is no need to know the absolute population densities. Relative densities serve the purpose equally well. In this case, population size is indirectly estimated without actually counting them. For example, the number of fishes caught per trap is good enough measure of its total population density in the lake. The tiger census in our National parks and tiger reserves is often based on pug marks (animal’s foot print) and faecal pellets.(c) : Sometimes, for certain ecological investigations, there is no need to know the absolute population densities. Relative densities serve the purpose equally well. In this case, population size is indirectly estimated without actually counting them. For example, the number of fishes caught per trap is good enough measure of its total population density in the lake. The tiger census in our National parks and tiger reserves is often based on pug marks (animal’s foot print) and faecal pellets.

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(d) : Sometimes, for certain ecological investigations, there is no need to know the absolute population densities. Relative densities serve the purpose equally well. In this case, population size is indirectly estimated without actually counting them. For example, the number of fishes caught per trap is good enough measure of its total population density in the lake. The tiger census in our National parks and tiger reserves is often based on pug marks (animal’s foot print) and faecal pellets.

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(b) : Immigration is the permanent inward movement of some individuals coming from outside into an existing population. This increases population density and would not limit its growth.

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(a) : Emigration is permanent outward movement of individuals from a population for settlement into a new area. It decreases the local population.

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(d) : \(A\) and \(B\) are natality and immigration. They add to population density. \(C\) and \(D\) are mortality and emigration. They decrease population density.

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(a) : Under normal condition births and deaths influence density of a population the other two factors being only active under special condition.

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(c) : If a new habitat is just being colonised, immigration may contribute more significantly to population growth than birth rates.

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(c)

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(b) : Intrinsic rate of natural increase (r)

\(
\begin{aligned}
& =\text { Birth rate }- \text { death rate } \\
& =0.15-0.08=0.07
\end{aligned}
\)

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(d) : If any species is flourishing under unlimited resources, it would reach exponential growth which can be depicted by equation:

\(
\frac{\mathrm{dN}}{\mathrm{dt}}=\mathrm{rN}
\)

Where, \(N=\) population density at time \(t ; r=\) intrinsic rate of natural increase.
If we derive the integral form of the exponential growth equation, it can be written as

\(
N_t=N_0 e^{t t}
\)

Where \(N_t=\) population density after time \(t ; N_0=\) population density at time zero; \(r=\) intrinsic rate of natural increase; \(\theta\) is the base of natural logarithm.

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(d)

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(c) : In nature, a given habitat has resources to support a certain number of individuals of a population, beyond which no further growth is possible. This limit is called nature’s carrying capacity (K) for that species in that habitat.

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(a)

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(b)

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(d)

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(d) : Competition is defined as the active demand by two or more individuals of the same species or members of different species at same trophic levels for a common resource. Intraspecific competition is competition amongst members of the same species for a common resource such as for food, space and mate. Interspecific competition is rivalry amongst members of different species. The severity of competition depends upon similarity in the requirement of food and shelter.

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(d)

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(a)

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(a) : Coevolution is caused by the selection pressures that each of the two species exerts on the other. Since there has been no coevolved herbivore with prickly pear cactus, it became abundant in Australia.

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(c) : Prey species have evolved various defenses to lessen the impact of predation. For plant, herbivores are the predators. Plants have evolved an astonishing variety of morphological and chemical defences against herbivores. Calotropis produces highly poisonous cardiac glycosides and that is why we never see any cattle or goat browsing on this plant.

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(c): Bacteria decompose the organic matter which is not really living. Hence, it cannot be considered as a prey-predator relationship.

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(d) : Competition keeps the population of inferior species under check. Superior barnacle, Balanus, nearly excluded the smaller barnacle, Chathamalus. If Balanus population is reduced, competition is released and Chathamalus population increases.

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(c): Two or more species with closely similar niche requirements cannot exist indefinitely in the same area as sooner or later they come into competition for possession of it. This is called Gause’s competitive exclusion principle, which states that an ecological niche cannot be simultaneously and completely occupied by established populations of more than one species. Two species can live in same habitat but not in the same niche. More similar the two niches are, severe the competition is.