NEET Biology: Ecology · Chapter 1

Organisms and Populations

What to remember

A population is a group of individuals of one species living in a defined area at the same time. Its main attributes are birth rate, death rate, sex ratio, age distribution and population density.
Population size changes as Nt+1 = Nt + [(B + I) − (D + E)]. Natality (B) and immigration (I) add individuals; mortality (D) and emigration (E) remove them.
Growth is exponential (J-shaped, dN/dt = rN) when resources are unlimited, and logistic (S-shaped, dN/dt = rN(K − N)/K) when resources are limited. K is the carrying capacity.
Species interact as mutualism (+/+), competition (−/−), predation (+/−), parasitism (+/−), commensalism (+/0) and amensalism (−/0).

Population attributes

A population has features that an individual does not have. An individual has a birth and a death. A population has a birth rate and a death rate. An individual is male or female. A population has a sex ratio.

Birth rate (natality) is the number of births per 1,000 individuals of the population per unit time. Death rate (mortality) is the number of deaths per 1,000 individuals per unit time. Both are expressed per individual of the population. For example, if 20 new individuals are born in a pond with 80 lotus plants in a year, the birth rate is 20/80 = 0.25 per plant per year.

Sex ratio is the proportion of males to females in the population. It is not always 1 : 1 and differs between species.

Age distribution. A population has individuals of different ages. The individuals are grouped into three age groups:

Pre-reproductive (young)
Reproductive (adult)
Post-reproductive (old)

The age distribution is shown as an age pyramid. The width of each bar is the number (or percentage) of individuals of that age group.

Type of pyramid	Shape	Pre-reproductive group	What it shows
Expanding	Triangle with a broad base	Largest	Population is growing
Stable	Bell shaped	About equal to the reproductive group	Population size stays about the same
Declining	Urn shaped, narrow base	Smallest	Population is shrinking

Population density is the number of individuals per unit area or volume. Examples: 200 Parthenium plants per hectare, or 5 million Chlamydomonas cells per mL of water. In some cases the number is not the best measure:

If a huge banyan tree and 200 small grass plants share an area, biomass is a better measure than number.
Percent cover is used for plants such as a dense algal bloom, where counting is hard.
Where a count is difficult, relative measures such as the number of fish caught per trap are used.
Tiger census uses indirect signs: pugmarks and faecal pellets.

Population density is not fixed. It changes with the four factors below.

Factor	Symbol	Effect on density
Natality	B	Increases
Immigration	I	Increases
Mortality	D	Decreases
Emigration	E	Decreases

Natality is the number of births during a given period. Mortality is the number of deaths during a given period. Immigration is the number of individuals of the same species that have come into the habitat from elsewhere. Emigration is the number of individuals of the population who left the habitat.

Population growth

Population size at time t+1 is given by:

Nt+1 = Nt + [(B + I) − (D + E)]

where Nt is the population density at time t. The population increases if (B + I) is greater than (D + E). Otherwise it decreases. Under normal conditions, B and D are the most important factors. I and E become important only in special conditions, such as when a new habitat is colonised.

Exponential growth. When resources (food and space) are unlimited, every individual can reproduce at full capacity and the population grows exponentially.

dN/dt = rN

Here N is the population size, t is time and r is the intrinsic rate of natural increase (the difference between birth rate and death rate per individual). Integrated form: Nt = N0 e^rt, where N0 is the density at time zero and e is the base of natural logarithms (2.71828). The graph of N against t is J-shaped. Standard values of r: Norway rat about 0.015 per year and flour beetle about 0.12 per day.

Logistic growth. No population in nature has unlimited resources. Resources become limiting, so the population cannot grow exponentially for a long time. The individuals that are better adapted survive and leave more offspring. A given habitat has enough resources for a maximum number of individuals. This limit is the carrying capacity (K).

dN/dt = rN [(K − N)/K]

The population first grows slowly (lag phase), then grows fast (exponential or log phase), then growth slows (deceleration phase) and finally levels off at K (stationary or asymptote phase). The graph is S-shaped (sigmoid). This model was proposed by Verhulst and Pearl, so it is called the Verhulst-Pearl logistic growth. It is the more realistic model because resources are limited in nature.

Feature	Exponential growth	Logistic growth
Resources	Unlimited	Limited
Equation	dN/dt = rN	dN/dt = rN (K − N)/K
Curve	J-shaped	S-shaped (sigmoid)
Carrying capacity	Not reached	Reached (N approaches K)
Realistic in nature	Only for a short time	Yes

When N is close to K, the term (K − N)/K is close to zero and growth stops. When N is very small compared to K, the term is close to 1 and the growth is nearly exponential.

Life history variation

Populations evolve to maximise their reproductive fitness (the Darwinian fitness or high r value) in the habitat in which they live. Selection acts on the life history traits. Life history traits differ among organisms:

Some organisms breed only once in their lifetime. Examples: Pacific salmon fish and bamboo.
Some breed many times during their lifetime. Examples: most birds and mammals.
Some produce a large number of small-sized offspring. Examples: oysters and pelagic fishes.
Some produce a small number of large-sized offspring. Examples: birds and mammals.

Which strategy is best depends on the habitat, food, predators and other factors. The question of why populations evolve one trait or the other is explained by the habitat conditions under which the population lives.

Population interactions

No species lives in isolation. Plants, animals and microbes interact in many ways. Interactions between two species are of six types. The signs show the effect on each species: + is beneficial, − is harmful, 0 is neutral.

Interaction	Species A	Species B
Mutualism	+	+
Competition	−	−
Predation	+	−
Parasitism	+	−
Commensalism	+	0
Amensalism	−	0

#### Predation

A predator feeds on its prey. Predators act as conduits for energy transfer from one trophic level to the next. They keep prey populations under control. When a species is introduced into a new area, it can become invasive if its predators are absent. The prickly pear cactus (Opuntia) introduced into Australia in the early 1920s spread over millions of hectares of rangeland. It was brought under control only after a cactus-feeding predator, the moth Cactoblastis cactorum, was introduced.

Predators also help in maintaining species diversity in a community by reducing the intensity of competition among competing prey species.

Prey species have evolved defences against predators:

Camouflage (cryptic colouration): some insects and frogs are difficult to spot against the background.
Poisonous or distasteful chemicals: the monarch butterfly is highly distasteful to its predator (a bird) because of a special chemical present in its body. The butterfly acquires this chemical during its caterpillar stage by feeding on a poisonous weed.
Warning colours: some animals are brightly coloured to advertise that they are distasteful.

Plant defences against herbivores. Herbivores are also predators. About 25 per cent of insects are phytophagous (plant-eaters). Plants have morphological and chemical defences:

Morphological: thorns (Acacia, Cactus).
Chemical: nicotine, caffeine, quinine, strychnine, opium and other substances. Many plants produce chemicals that make them unpalatable or toxic.
Calotropis (a weed) produces highly poisonous cardiac glycosides, so cattle and goats do not eat it.

#### Competition

Competition occurs when closely related species compete for the same resources that are limited. It can also occur when resources are not limited, if one species reduces the feeding efficiency of the other. Competition between unrelated species is also possible. Example: flamingoes and resident fishes in South American lakes compete for zooplankton.

Gause's competitive exclusion principle: two closely related species competing for the same resources cannot coexist indefinitely. The competitively inferior one is eliminated eventually. This is proved in laboratory experiments with Paramecium species.

Examples from nature:

The Abingdon tortoise in the Galapagos Islands became extinct within a decade after goats were introduced. The goats were better at browsing.
Connell's field experiment with two barnacle species on the rocky sea coast of Scotland: Chthamalus is dominant in the upper intertidal zone and Balanus is dominant in the lower zone. When Balanus was removed, Chthamalus spread to the lower zone. So Balanus competitively excluded Chthamalus from the lower zone.

Resource partitioning. Two species competing for the same resources may avoid competition by choosing different times for feeding or different foraging patterns. MacArthur showed that five closely related species of warblers living on the same tree were able to coexist because each had a different foraging activity in a different part of the tree canopy.

#### Parasitism

In parasitism, the parasite lives on or in the host and obtains food from it. The parasite harms the host, but usually does not kill it quickly.

Host specificity: parasites have evolved to be host-specific, living on a single host species. They adapt to the host's body, for example by loss of unnecessary sense organs, development of adhesive organs or suckers, loss of digestive system and a high reproductive capacity.
Ectoparasites feed on the external surface of the host. Examples: lice on humans, ticks on dogs, and copepods on marine fish.
Endoparasites live inside the host body, such as in the liver, kidney, lungs or red blood cells. Examples: liver fluke and tapeworm.
Brood parasitism: a bird lays its eggs in the nest of another bird and lets the host incubate them. The eggs of the parasite resemble the host's eggs in size and colour, so the host does not detect and eject them. Example: the cuckoo (koel) lays its eggs in the crow's nest.
Parasites that reduce the survival, growth and reproduction of the host and reduce its population density are considered harmful for the host population.
The life cycle of parasites is often complex. Many parasites need two or more hosts.

#### Commensalism

One species benefits and the other is neither harmed nor benefited.

An orchid growing as an epiphyte on a mango branch.
Barnacles growing on the back of a whale.
The cattle egret and grazing cattle. The egrets forage close to the cattle and feed on the insects flushed out by the cattle's movement.
The sea anemone with stinging tentacles and the clown fish: the fish gets protection from predators because those stay away from the stinging tentacles; the sea anemone does not appear to get any benefit.

#### Mutualism

Both interacting species benefit.

Lichens: a close association between a fungus and photosynthetic algae or cyanobacteria. The fungus absorbs nutrients and water for the partner. The photosynthetic partner makes food for the fungus.
Mycorrhizae: an association between fungi and the roots of higher plants. The fungus helps the plant to absorb essential nutrients (such as phosphorus) from the soil. The plant provides the fungus with energy-yielding carbohydrates.
Fig and wasp: plant-animal mutualism. Fig trees are pollinated only by a species-specific wasp. The female wasp pollinates the fig inflorescence while searching for suitable egg-laying sites. In return the fig offers the wasp some developing seeds as food for the larvae.
Mediterranean orchid Ophrys: one petal of its flower bears a resemblance to the female of a bee in size, colour and markings. The male bee is attracted to what it perceives as a female (pseudocopulation) and is dusted with pollen. When the same bee visits another flower, it transfers the pollen and pollinates it. If the female bee's colour patterns change slowly during evolution, the pollination success of the orchid will be reduced unless the orchid flower co-evolves. This is an example of co-evolution of the mutualists. Here the flower mimics the bee; the bee does not get food, so it is a case of sexual deceit.

#### Amensalism

One species is harmed and the other is not affected. Example: a bacterium-inhibiting chemical produced by the fungus Penicillium harms bacteria, while the fungus is not affected.

Association	Example	Effect
Mutualism	Lichen, mycorrhiza, fig and wasp, Ophrys and bee	+ / +
Competition	Abingdon tortoise and goat; Balanus and Chthamalus	− / −
Predation	Cactoblastis and prickly pear	+ / −
Parasitism	Cuckoo and crow; tapeworm and human	+ / −
Commensalism	Orchid on mango; cattle egret and cattle	+ / 0
Amensalism	Penicillium and bacteria	− / 0

NEET traps

1. Exponential vs logistic curve: J-shaped goes with dN/dt = rN and unlimited resources; S-shaped goes with the term (K − N)/K and limited resources.
2. r vs K: r is the intrinsic rate of natural increase (births minus deaths per individual); K is the carrying capacity (maximum population size).
3. Competition vs predation signs: competition is −/−; predation is +/−.
4. Commensalism vs mutualism: in commensalism one partner is neutral (0). Cattle egret and orchid on mango are commensalism; lichen and mycorrhiza are mutualism.
5. Amensalism vs commensalism: amensalism is −/0 (one harmed); commensalism is +/0 (one benefited).
6. Ectoparasite vs endoparasite: lice, ticks and copepods are ectoparasites; liver fluke and tapeworm are endoparasites.
7. Brood parasitism: the cuckoo (koel) lays eggs in the crow's nest; the crow is the host. Do not reverse them.
8. Chthamalus vs Balanus: Chthamalus is in the upper intertidal zone; Balanus is in the lower zone and is the stronger competitor.
9. Pyramid shape: expanding is a triangle with a broad base, stable is bell shaped, declining is urn shaped.
10. Immigration vs emigration: immigration adds individuals to the habitat; emigration removes them.

One-liners

1. A population is a group of individuals of one species in a given area.
2. Sex ratio is the proportion of males to females.
3. The three age groups are pre-reproductive, reproductive and post-reproductive.
4. A bell-shaped age pyramid means a stable population.
5. An urn-shaped age pyramid means a declining population.
6. Tiger census uses pugmarks and faecal pellets.
7. Nt+1 = Nt + [(B + I) − (D + E)].
8. In dN/dt = rN, r is the intrinsic rate of natural increase.
9. Exponential growth gives a J-shaped curve.
10. Verhulst and Pearl proposed the logistic S-shaped model.
11. Pacific salmon and bamboo breed only once in a lifetime.
12. Cactoblastis cactorum controlled prickly pear in Australia.
13. Gause's principle: closely related species with the same resource needs cannot coexist for long.
14. MacArthur studied five warbler species and resource partitioning.
15. Ophrys flowers mimic female bees; fig trees depend on specific wasps.

Practice questions

Which age pyramid shape is expected for a rapidly growing population?
1. Triangle with a broad base
2. Urn shaped with a narrow base
3. Rectangle with bars of equal width
4. Bell shaped
Answer
A. Triangle with a broad base
An expanding population has many pre-reproductive individuals, so the base is broad and the pyramid is triangular.
The intrinsic rate of natural increase of a population is represented by
1. N
2. B
3. K
4. r
Answer
D. r
In dN/dt = rN, r is the intrinsic rate of natural increase, the difference between birth rate and death rate per individual.
The graph of population size against time under exponential growth is
1. A straight horizontal line
2. S-shaped
3. J-shaped
4. Bell shaped
Answer
C. J-shaped
With unlimited resources, dN/dt = rN gives a J-shaped curve.
Which organism was used to control the spread of prickly pear in Australia?
1. The cattle egret
2. The moth Cactoblastis cactorum
3. The cuckoo
4. The Abingdon tortoise
Answer
B. The moth Cactoblastis cactorum
Opuntia was controlled after the cactus-feeding moth Cactoblastis cactorum was introduced.
In brood parasitism, the koel lays its eggs in the nest of the
1. barnacle
2. sparrow
3. cattle egret
4. crow
Answer
D. crow
The cuckoo (koel) is the brood parasite and the crow is the host that incubates the eggs.
The Verhulst-Pearl logistic growth equation is
1. dN/dt = rN (K − N)/K
2. dN/dt = rN
3. dN/dt = rN (N − K)/K
4. dN/dt = (K − N)/rN
Answer
A. dN/dt = rN (K − N)/K
The logistic model adds the factor (K − N)/K to the exponential equation, so growth slows as N approaches K.
Which of the following breeds only once in its lifetime?
1. Human
2. Oyster
3. Pacific salmon
4. Crow
Answer
C. Pacific salmon
Pacific salmon and bamboo breed once; most birds and mammals breed many times.
A cattle egret foraging near grazing cattle is an example of
1. mutualism
2. commensalism
3. amensalism
4. competition
Answer
B. commensalism
The egret benefits from the insects flushed out by cattle, while the cattle are neither harmed nor benefited.
In the intertidal zone of the Scottish coast, Chthamalus is dominant in the
1. lower zone
2. open sea only
3. both zones equally
4. upper zone
Answer
D. upper zone
Chthamalus occupies the upper intertidal zone; Balanus dominates the lower zone.
In a mycorrhizal association, the fungus helps the plant mainly by
1. absorbing nutrients such as phosphorus from the soil
2. fixing atmospheric nitrogen into nitrates
3. supplying energy-yielding carbohydrates
4. protecting the roots from predators
Answer
A. absorbing nutrients such as phosphorus from the soil
The fungus absorbs phosphorus and other nutrients; the plant supplies carbohydrates to the fungus.
MacArthur's study of five warbler species on the same tree demonstrated
1. competitive exclusion
2. camouflage
3. resource partitioning
4. brood parasitism
Answer
C. resource partitioning
The warblers avoided competition by foraging in different parts of the tree.
Which plant is avoided by goats and cattle because it produces cardiac glycosides?
1. Pisum
2. Calotropis
3. Acacia
4. Opuntia
Answer
B. Calotropis
Calotropis produces highly poisonous cardiac glycosides, so herbivores do not eat it.
The interaction in which one species is harmed and the other is unaffected is
1. mutualism
2. amensalism
3. commensalism
4. parasitism
Answer
B. amensalism
Amensalism is -/0. Commensalism is +/0.
Which of the following is an ectoparasite?
1. Liver fluke
2. Cuckoo chick in a crow's nest
3. Tick on a dog
4. Tapeworm
Answer
C. Tick on a dog
Ticks live on the outside of the host. Liver fluke and tapeworm are endoparasites.
Which of the following is a mutualistic association?
1. Fig tree and its wasp
2. Orchid on a mango branch
3. Barnacles on a whale
4. Cuckoo and crow
Answer
A. Fig tree and its wasp
In the fig-wasp relationship both partners benefit; the other three are commensalism or parasitism.
In logistic growth, the phase that follows the lag phase is the
1. death phase
2. stationary phase
3. deceleration phase
4. exponential (log) phase
Answer
D. exponential (log) phase
Growth is slow in the lag phase, then rapid in the exponential phase, then slows and stops near K.
Given below are two statements: Statement I: Birth rate and death rate are attributes of a population and not of an individual. Statement II: The sex ratio is exactly 1 : 1 in all populations. Choose the correct answer.
1. Both Statement I and Statement II are correct
2. Both Statement I and Statement II are incorrect
3. Statement I is correct but Statement II is incorrect
4. Statement I is incorrect but Statement II is correct
Answer
C. Statement I is correct but Statement II is incorrect
Sex ratio differs between species; it is not always 1 : 1.
Given below are two statements: Statement I: Exponential growth gives an S-shaped curve. Statement II: Logistic growth approaches the carrying capacity. Choose the correct answer.
1. Both Statement I and Statement II are correct
2. Both Statement I and Statement II are incorrect
3. Statement I is correct but Statement II is incorrect
4. Statement I is incorrect but Statement II is correct
Answer
D. Statement I is incorrect but Statement II is correct
Exponential growth is J-shaped; logistic growth is S-shaped and levels off at K.
Given below are two statements: Statement I: Chthamalus excludes Balanus from the lower intertidal zone. Statement II: The eggs of a brood parasite differ greatly in colour from the host's eggs. Choose the correct answer.
1. Both Statement I and Statement II are correct
2. Both Statement I and Statement II are incorrect
3. Statement I is correct but Statement II is incorrect
4. Statement I is incorrect but Statement II is correct
Answer
B. Both Statement I and Statement II are incorrect
Balanus excludes Chthamalus from the lower zone; parasite eggs resemble the host's eggs.
Given below are two statements: Statement I: Parasites are generally host-specific. Statement II: Ectoparasites live inside the body of the host. Choose the correct answer.
1. Both Statement I and Statement II are correct
2. Both Statement I and Statement II are incorrect
3. Statement I is correct but Statement II is incorrect
4. Statement I is incorrect but Statement II is correct
Answer
C. Statement I is correct but Statement II is incorrect
Ectoparasites live on the external surface of the host.
Given below are two statements: Statement I: In commensalism of cattle egret and cattle, the cattle are harmed. Statement II: In an orchid growing on a mango branch, the mango is neither harmed nor benefited. Choose the correct answer.
1. Both Statement I and Statement II are correct
2. Both Statement I and Statement II are incorrect
3. Statement I is correct but Statement II is incorrect
4. Statement I is incorrect but Statement II is correct
Answer
D. Statement I is incorrect but Statement II is correct
Commensalism is +/0, so the cattle and the mango are not harmed.
Given below are two statements: Statement I: Lichens are a mutualism between a fungus and an alga or cyanobacterium. Statement II: Mycorrhiza is an association between fungi and the roots of higher plants. Choose the correct answer.
1. Both Statement I and Statement II are correct
2. Both Statement I and Statement II are incorrect
3. Statement I is correct but Statement II is incorrect
4. Statement I is incorrect but Statement II is correct
Answer
A. Both Statement I and Statement II are correct
Both statements are correct mutualisms.
Given below are two statements: Statement I: The flower of Ophrys gives nectar to the male bee as a reward. Statement II: Fig trees are pollinated by any insect visiting them. Choose the correct answer.
1. Both Statement I and Statement II are correct
2. Both Statement I and Statement II are incorrect
3. Statement I is correct but Statement II is incorrect
4. Statement I is incorrect but Statement II is correct
Answer
B. Both Statement I and Statement II are incorrect
Ophrys deceives the male bee by mimicking a female, and fig trees depend on a species-specific wasp.
Which of the following statements about the logistic growth model are correct? 1. K is the carrying capacity of the habitat. 2. Growth slows as N approaches K. 3. It assumes that resources are unlimited.
1. 2 and 3 only
2. 1 and 2 only
3. 1 and 3 only
4. 1, 2 and 3
Answer
B. 1 and 2 only
Logistic growth assumes limited resources; the third statement describes exponential growth.
Which of the following statements about predation are correct? 1. Predators help to keep prey populations under control. 2. Camouflage is a prey defence. 3. Predators can reduce competition among competing prey species.
1. 1 and 2 only
2. 2 and 3 only
3. 1 and 3 only
4. 1, 2 and 3
Answer
D. 1, 2 and 3
All three are correct; predation is a +/- interaction that also helps maintain species diversity.
Assertion (A): Chthamalus is absent from the lower intertidal zone when Balanus is present. Reason (R): Balanus competes more successfully and excludes Chthamalus from that zone.
1. Both A and R are true and R is the correct explanation of A
2. Both A and R are true but R is not the correct explanation of A
3. A is true but R is false
4. A is false but R is true
Answer
A. Both A and R are true and R is the correct explanation of A
Balanus is the stronger competitor in the lower zone; removing it allowed Chthamalus to spread.
Assertion (A): Pacific salmon breed only once in their lifetime. Reason (R): Bamboo flowers only once in its life.
1. Both A and R are true and R is the correct explanation of A
2. Both A and R are true but R is not the correct explanation of A
3. A is true but R is false
4. A is false but R is true
Answer
B. Both A and R are true but R is not the correct explanation of A
Both are true, but one fact does not explain the other.
Assertion (A): Fig trees depend on a species-specific wasp for pollination. Reason (R): Fig trees are wind-pollinated.
1. Both A and R are true and R is the correct explanation of A
2. Both A and R are true but R is not the correct explanation of A
3. A is true but R is false
4. A is false but R is true
Answer
C. A is true but R is false
The female wasp pollinates the fig inflorescence while laying eggs, so R is false.
Assertion (A): Exponential growth can continue for ever in nature. Reason (R): Exponential growth occurs when resources are unlimited.
1. Both A and R are true and R is the correct explanation of A
2. Both A and R are true but R is not the correct explanation of A
3. A is true but R is false
4. A is false but R is true
Answer
D. A is false but R is true
Resources are limited in nature, so exponential growth cannot continue for long.
Assertion (A): Birds avoid eating the monarch butterfly. Reason (R): The caterpillar acquires a distasteful chemical by feeding on a poisonous weed.
1. Both A and R are true and R is the correct explanation of A
2. Both A and R are true but R is not the correct explanation of A
3. A is true but R is false
4. A is false but R is true
Answer
A. Both A and R are true and R is the correct explanation of A
The chemical stored from the weed makes the butterfly unpalatable.
Assertion (A): An orchid growing on a mango branch is an example of commensalism. Reason (R): Both the orchid and the mango benefit from the association.
1. Both A and R are true and R is the correct explanation of A
2. Both A and R are true but R is not the correct explanation of A
3. A is true but R is false
4. A is false but R is true
Answer
C. A is true but R is false
The orchid benefits and the mango is neither harmed nor benefited, so R is false.
Match List I with List II. List I: a. Mutualism b. Competition c. Predation d. Commensalism List II: i. Cattle egret and cattle ii. Lichen iii. Cactoblastis and prickly pear iv. Goats and the Abingdon tortoise Choose the correct answer.
1. a-ii, b-iv, c-iii, d-i
2. a-i, b-ii, c-iii, d-iv
3. a-ii, b-iv, c-i, d-iii
4. a-ii, b-i, c-iii, d-iv
Answer
A. a-ii, b-iv, c-iii, d-i
Lichen is mutualism, goats and tortoise is competition, Cactoblastis and prickly pear is predation, egret and cattle is commensalism.
Match List I with List II. List I: a. Mutualism b. Parasitism c. Commensalism d. Amensalism List II: i. +/0 ii. +/+ iii. −/0 iv. +/− Choose the correct answer.
1. a-i, b-ii, c-iv, d-iii
2. a-ii, b-i, c-iv, d-iii
3. a-ii, b-iv, c-iii, d-i
4. a-ii, b-iv, c-i, d-iii
Answer
D. a-ii, b-iv, c-i, d-iii
Mutualism +/+, parasitism +/−, commensalism +/0, amensalism −/0.
Match List I with List II. List I: a. Cuckoo b. Cactoblastis c. Chthamalus d. Ophrys List II: i. Upper intertidal zone ii. Sexual deceit in pollination iii. Brood parasite iv. Moth that feeds on prickly pear Choose the correct answer.
1. a-iii, b-ii, c-i, d-iv
2. a-iii, b-iv, c-i, d-ii
3. a-i, b-iii, c-iv, d-ii
4. a-ii, b-iv, c-i, d-iii
Answer
B. a-iii, b-iv, c-i, d-ii
Cuckoo is a brood parasite, Cactoblastis feeds on prickly pear, Chthamalus is in the upper zone, Ophrys uses sexual deceit.
Match List I with List II. List I: a. Natality b. Mortality c. Immigration d. Emigration List II: i. Individuals leaving the habitat ii. Births iii. Deaths iv. Individuals entering from elsewhere Choose the correct answer.
1. a-i, b-ii, c-iv, d-iii
2. a-ii, b-i, c-iv, d-iii
3. a-ii, b-iii, c-iv, d-i
4. a-ii, b-iv, c-iii, d-i
Answer
C. a-ii, b-iii, c-iv, d-i
Natality is births, mortality is deaths, immigration is entering and emigration is leaving.
Match List I with List II. List I: a. Lice on humans b. Liver fluke c. Copepod on fish d. Cuckoo List II: i. Brood parasite ii. Endoparasite iii. Ectoparasite of humans iv. Ectoparasite of marine fish Choose the correct answer.
1. a-iii, b-ii, c-iv, d-i
2. a-ii, b-iii, c-iv, d-i
3. a-iii, b-ii, c-i, d-iv
4. a-i, b-ii, c-iii, d-iv
Answer
A. a-iii, b-ii, c-iv, d-i
Lice are human ectoparasites, liver fluke is an endoparasite, copepods are fish ectoparasites and the cuckoo is a brood parasite.
Match List I with List II. List I: a. r b. K c. dN/dt = rN d. dN/dt = rN (K − N)/K List II: i. Carrying capacity ii. Logistic growth iii. Intrinsic rate of natural increase iv. Exponential growth Choose the correct answer.
1. a-iii, b-ii, c-iv, d-i
2. a-i, b-ii, c-iv, d-iii
3. a-ii, b-i, c-iv, d-iii
4. a-iii, b-i, c-iv, d-ii
Answer
D. a-iii, b-i, c-iv, d-ii
r is the intrinsic rate of increase, K the carrying capacity, dN/dt = rN is exponential and the other is logistic.
In a pond, 8 new lotus plants are born in a year in a population of 80 plants. The birth rate per plant per year is
1. 10
2. 0.8
3. 0.1
4. 0.01
Answer
C. 0.1
Birth rate = 8/80 = 0.1 per plant per year.
A population has Nt = 500. During the next interval B = 50, D = 30, I = 10 and E = 20. What is Nt+1?
1. 510
2. 480
3. 540
4. 590
Answer
A. 510
Nt+1 = 500 + [(50 + 10) − (30 + 20)] = 500 + 10 = 510.
In a population growing logistically, N is almost equal to K. What happens to the growth rate dN/dt?
1. It becomes equal to rN
2. It becomes close to zero
3. It becomes strongly negative
4. It becomes maximum
Answer
B. It becomes close to zero
When N approaches K, (K − N)/K approaches zero, so growth stops.
Balanus is removed from the lower intertidal zone of a rocky coast. What is expected for Chthamalus?
1. It disappears from the upper zone
2. It spreads into the lower zone
3. It stays only in the upper zone
4. It becomes a parasite of Balanus
Answer
B. It spreads into the lower zone
Balanus had excluded Chthamalus from the lower zone, so removing it allows Chthamalus to spread.
Two closely related species with the same food are kept together in a flask with a limited food supply. After some generations only one species remains. This is explained by
1. competitive exclusion
2. mutualism
3. resource partitioning
4. brood parasitism
Answer
A. competitive exclusion
Gause's principle: the competitively inferior species is eliminated.
An age pyramid has a very narrow base and larger reproductive and post-reproductive bars (urn shaped). The population is most likely
1. expanding
2. growing exponentially
3. stable
4. declining
Answer
D. declining
A small pre-reproductive group means few future parents, so the population is declining.
Which method is suitable for estimating a tiger population in a forest?
1. Counting the number caught in traps per hour
2. Measuring percent cover
3. Counting pugmarks and faecal pellets
4. Weighing the total biomass of tigers
Answer
C. Counting pugmarks and faecal pellets
A tiger census uses indirect signs such as pugmarks and faecal pellets.

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