Organisms and Population Test 10

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Organisms and Population Test 10

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Question 1
1 / -0

The density of a population in a given habitat during a given period, fluctuates due to changes in certain basic processes. On this basis, fill up boxes A and B in the given flow chart with correct option.

A
A — Natality, B — Mortality

B
A — Immigration , B — Emigration

C
A — Natality, B — Immigration

D
Both (a) and (b)

Solution

Natality and Immigration add to the population density. Mortality and emigration decrease the population density.
Question 2
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What does the shape of the given age pyramids reflects about the growth status of the related population?

A
(i) - Expanding (ii) - Stable

B
(i) - Stable (ii) - Declining

C
(i) - Expanding (ii) - Declining

D
(i) - Declining (ii) - Stable

Solution

Triangular age pyramid has high proportion of reproductive 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 where growth rate is nearly zero.
Question 3
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The population growth is generally described by the following equation:

What does 'r' represent in the given equation?

A
Population density at time 't'

B
Intrinsic rate of natural increase

C
Carrying capacity

D
The base of natural logarithm

Solution

A population growing in a habitat with limited resources shows initially a lag phase, followed by phases of increase and decrease and finally the population density reaches the carrying capacity. A plot of N in relation to time (t) results in a sigmoid curve. This type of population growth is called Verhulst- Pearl Logistic Growth as explained by the following equation:
Where N = Population density at a time t;
r = Intrinsic rate of natural increase and;
K = Carrying capacity.
Question 4
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The plant-animal interactions often involve co-evolution of the mutualists so that

A
the mutually beneficial system could be safeguarded against 'cheaters'

B
a given plant species can be pollinated only by its partner animal species and no other species

C
the animal utilises plant not only for ovipositions but also to pollinate the plant

D
all of these

Solution

Plant-animal interactions involve co-evolution of mutualists. This means, the evolution of the plant (e.g., flower) and the animal (e.g. pollinator species) are closely linked with one another.
Question 5
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Which type of interaction is represented by the given figure?

A
Mutualism

B
Parasitism

C
Helotism

D
Amensalism

Solution

Mutualism is an association between individuals of two species, both of which are benefitted. The species participating in mutualism are called mutualists. Sea anemone, Adamsia is habitually found fastened by its characteristically lobed pedal disc to the snail's shell used as a portable home by the hermit crab (Eupagurus prideauxi). The anemone protects the crab from the enemies with its nematocysts. In return, the anemone receives pieces of food dropped by the crab and is carried to new places by it. Other examples of mutualism are mycorrhiza living on roots of higher plants and wasp pollinating fig inflorescence.
Question 6
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Species interaction with negative influence on both is referred to as

A
amensalism

B
mutualism

C
commensalism

D
competition

Solution

Competition is defined as the active demand by two or more individuals of the same species or members of two or more species at same trophic levels for a common resource. Intraspectific 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.
Question 7
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In a pond, last year there were 30 lotus plants. Through reproduction, 25 new lotus plants were added in one year while 8 plants died. The birth and death rates for the lotus population respectively are ___ and ____ individuals per lotus per year.

A
0.83 , 0.26

B
0.26, 0.83

C
0.25 , 0.80

D
0.80, 0.25

Solution

Total number of plants (in the beginning ) = 30
New plants added by reproduction = 25
Birth rate (of a population)

=0.83 individuals per lotus per year
Number of plants died =8
Question 8
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Which of the following is not an example of using relative density to measure population density in a certain area?

A
Counting pugmarks of tigers to find population density of tigers in a forest

B
Counting the number of fishes caught in a trap to find population density of fishes in a lake

C
Measuring biomass of bacterial culture to find out population density of bacteria in a petri dish

D
Measuring biomass of phytoplanktons in 1cc water to find out population density of phytoplanktons in a lake

Solution

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.
Question 9
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Total number of individuals of a species per unit area and per unit time is called:

A
Population size

B
Population density

C
Demography

D
Population dynamics

Solution

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 kilometer, number of trees per acre in a forest, etc.
Question 10
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Percentage of individuals of a given age group in a given population is called as

A
age distribution

B
age density

C
age graph

D
age curve

Solution

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 as age pyramid.
Question 11
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Population ecology is an important area because it _____(i)_______ ecology to population genetics and _____(ii)________
identify (i) and (ii) in the above statement and select the correct option.

A
a

B
b

C
c

D
d

Solution

Population ecology is the subfield of ecology that deals with the dynamics of species populations and how these populations interact with the environment. It is an important area because it links the ecology to population genetics and is responsible for evolution.
Question 12
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In a given population of 2000 individuals, 80 births and 125 deaths were reported over a given period of time. Which of the following graphs will correspond to it?

A

B

C

D

Solution

Number of deaths is more than the number of births, showing a declining population.
Question 13
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Parameters related to age structure include

A
fecundity (birth rate)

B
generation time

C
death rate

D
all of these

Solution

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 time are important related to it.
Question 14
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The age structures of a population influences population growth because

A
younger females have more offsprings than do older females

B
different ae groups have different reproductive capabilities

C
more is the number of immature individuals, slower is the growth of population

D
a shorter generation time results is slower population growth

Solution

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 increas in population. Reproductive individuals are the ones which are actually adding neq members to the population. Post-reproductive individuals are older individuals which no longer take part in reproduction.
Question 15
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Which of the following factors has a negative effect on the population growth rate?

A
Emigration

B
Immigration

C
Natality

D
Fecundity

Solution

migration is permanent outward movement of individuals from a population for settlement into a new area. If decreases the local population.
Question 16
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If N population density at time t, then population density at time t+1 can be written as
N_t ₊₁=N_t +[(A+B)−(C+D)]
Select the correct option for A, B, C and D in the above equation.

A
A can be mortality and B can be natality

B
B can be immigration and C can be natality

C
C can be mortality and D can be immigration

D
A can be natality and D can be emigration

Solution

A and B are natality and immigration. They add to population density. C and D are mortality and emigration. They decrease population density.
Question 17
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Which of the following is not a factor that would limit the growth of a population?

A
Food shortage

B
Immigration

C
Disease

D
Famine

Solution

Immigration is the permanent inward movement of some individuals coming from outside into an existing population. This increase population density and would not limit its growth.
Question 18
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The given figure represents different factors affecting population density (N) If B = nasality, D = mortality, E = emigration and I = immigration; then select the incorrect option regarding these.

A
B and D are most influential factors under normal conditions while I and E become important in special conditions

B
In a new habitat just being colonised, I become more important than B

C
B and I cause positive changes in N

D
I is generaly equal to E

Solution

Immigration is not necessarily equal to emigration in a population.
Question 19
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Exponential growth is observed in a population when

A
resources in the habitat are unlimited

B
each species has the ability to realise its full innate potential

C
both (a) and (b)

D
none of these

Solution

When food and space for a population are unlimited, each species has the ability to realise fully its inherited potential to grow. Then the population grows in an exponential or geometric ratio.
Question 20
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In a population per capita birth rate is 0.15 and per capita death rate is 0.08 during a unit time period. What is the value of r (intrinsic rate of natural increase) for the given population?

A
0.023

B
0.07

C
0.05

D
0.25

Solution

Intrinsic rate of natural increase (r)
= Birth rate − death rate
=0.15−0.08=0.07