(3)

(4)

Gause’s competitive exclusion principle states that two closely related species competing for the same resources cannot co-exist indefinitely and the competitively inferior one will be eliminated eventually. This may be true if resources are limiting, but not otherwise.

(4)

The relationship between plants and animals is the most spectacular and evolutionarily fascinating example of mutualism. Plants need the help of animals for pollinating their flowers and dispersing their seeds. Animals get rewards in the form of pollen and nectar for pollinators and juicy and nutritious fruits for seed dispersers.

(2)

Total number of snails in a pond (in the beginning) = 250

Total number of snails after a year = 2500

Number of snails added = 2500 - 250 = 2250

Birth rate = New snails added / Total number of snails in the beginning = 2250 / 250 = 9 individuals per snail per year

(1)

Calotropis plant produces highly poisonous cardiac glycosides as a defence against herbivores. Thus, herbivores do not browse on this plant.

(4)

(1)

In general, herbivores and plants appear to be more adversely affected by competition than carnivores.

(3)

Logistic growth → Limited resource availability condition

Exponential growth → Unlimited resource availability condition

Expanding age pyramid → The percent individuals of pre-reproductive age is largest followed by reproductive and post-reproductive age groups

Stable age pyramid → The Percent individuals of pre-reproductive and reproductive age groups are same

(3)

A leopard and a lion in a forest/grassland → Competition

A cuckoo laying egg in a crow’s nest → Brood parasitism

Fungi and root of higher plant in mycorrhizae → Mutualism

A cattle egret and a cattle in a field → Commensalism

(3)

In predation one species derives benefit while the other one is harmed. So, in this type of population interaction one species is positively impacted, whereas another one is negatively impacted.

(1)

In predation, only one species benefits and the other is harmed.

(1)

Death rate in the given population of Drosophila during given time interval is $=\frac{8}{80}=0.1$

(2)

If two species compete for the same resource, they could avoid competition by choosing different times for feeding or different foraging patterns. This is called resource partitioning.

(2)

Amensalism is an interaction in which one species is harmed and other is unaffected.

(4)

In the exponential growth equation, ${\mathrm{N}}_{\mathrm{t}}= {\mathrm{N}}_0{\mathrm{e}}^{\mathrm{rt}}$. Here $\mathrm{e}$ is base of natural logarithms (2.71828).

(4)

(3)

(4)

Female wasp and fig species is an example of mutualism.

(2)

Natality refers to the number of births during a given period in the population that are added to the initial density. Death rate or mortality is the number of deaths in the population during a given time period. Immigration is the number of individuals entering a habitat. Emigration is the number of individuals of the population that left the habitat and had gone elsewhere during a time period.

(2)

Yucca has an obligate mutualism with a species of moth, i.e., Pronuba. The only pollinator of this plant is the Yucca moth. The Yucca moth is likewise dependent upon the Yucca plant as Yucca moth caterpillars need to eat Yucca seed only or starve.

(1)

In a population where the number of pre-reproductive individuals or the younger individual is larger than the reproductive individuals, the population will increase.

(4)

Amensalism is a relationship between organisms of different species in which an organism does not allow other organism to grow or live near it. Inhibition is achieved through the secretion of chemicals called allelochemics. Antibiotics are a kind of allelochemics produced by some microbes which in small concentration can kill or retard growth of harmful microbes without adversely affecting the host.

(1)

Asymptote in a logistic growth curve is obtained when carrying capacity (K) reaches the population density (N), i.e., K = N.

(3)

Mycorrhiza is a mutualistic interaction between a fungus and roots of higher plants.

(1)

Organisms that are r-selected (r-strategists) able to colonise a habitat rapidly, utilising the food and other resources before other organisms are established and begin to compete. The r-strategists tend to be relatively small organisms with short life spans (e.g., bacteria) and often live in temporary or unstable environments; characteristically their survival depends on their ability to produce large numbers of offspring rather than on their ability to compete.

(4)

Parasitism is an association in which one organism (the parasite) lives on (ectoparasitism) or in (endoparasitism) the body of another organism (host), from which it obtains its nutrients. This association is beneficial for the parasites as they get continuous supply of nutrients from their host and are able to rapidly multiply their numbers. But it is detrimental for the host organism as parasitic infection leads to various complications and diseases in the host body may also be fatal to the host under certain circumstances.

(2)

(3)

(1)

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 as Gause’s principle of competitive exclusion, 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.

(3)

Competition is the rivalry between two or more organisms for obtaining the same resources such as food, light, water, space, shelter, mate, etc. Competitors adversely affect each other.