Answer: Option D. -> Niche
:
D
An ecological nichecan be consideredthe habitat of an organism, but it is not merely a spatial term, when an organism occupies a habitat it has certain behavioral adaptations that enable it to fit well into that habitat. The organism then interacts with the environment and takes on an ecological role that modifies and alters its habitat. Therefore an ecological niche can be defined as the functionof an organism in its habitat.

Answer: Option A. -> Both A and R are correct and R explains A
:
A
The case of red milk snake mimicking the coral snake is called Batesian Mimicry. The red milk snake is not venomous, however, it mimics the appearance of the venomous coral snake. The predators confuse red milk snake to be venomous and stay away from it.

Answer: Option A. -> An overwhelming majority of animals and nearly all plants maintain a constant internal temperature
:
A
Warm blooded animals like birds and mammalsare the only animals that can maintain a constant internal temperature, most of the animals do not regulate their internal temperature.
The largest purely terrestrial animal found in Antarctica is a flightless midge (a flightless fly) that grows no more than 13mm in length. All other Antarctic animals are either smaller than this or migrate spending some of the year away from the deep south and the extreme cold. They either swim or fly away - and back again.
An orchid growing as an epiphyte on a mango branch is an example of commensalism, because the orchid derives its nourishment from the mango tree, but the mango tree however is not harmed.

Answer: Option D. -> 0
:
D
In a logistic growth curve, the rate of change in population size dN/dt = rN (1-(N/K)). Here if the value of N approaches K, then the equation will become dN/dt = rN ((K/K) - (K/K)), which is equal to 0. Whereas in the intial phase of growth when N is very small, N/K is negligent and the equation will be dN/dt = rN (1) = rN

Answer: Option D. -> Commensalism
:
D
Commensalism is a relationship which is beneficial to one organism and the other is unaffected. Barnacles growing on the back of a whale gets protection and more access to food due to its relationship with the whale, while the whale is unaffected by this relationship, therefore, this relationship is commensalism. Mutualism is a relationship where both the organisms benefit. Ammensalism is where one organism is harmed while the other is unaffected and parasitism is when one organism lives off another, this relationship is beneficial to one, and harmful to the host partner.

Answer: Option B. -> Population
:
B
A population is a group of individuals of the same species inhabiting the same area. A biome on the other hand is a large ecological area having the same climate. Ecosystem is thebasic unit of ecology, consisting of a group of interconnected elements, formed by the interaction of a community of organisms with their environment. Community is a group of interacting populations.

Answer: Option A. -> Both statements 1 and 2 are correct and statement 2 is the correct explanation of statement 1.
:
A
Calotropis commonly known as milkweed is a very poisonous and unpalatable plant. Therefore it is avoided by cattle or goats. The plant however is the sustenance for many species of caterpillars such as viceroy and monarchs butterfly.

Answer: Option B. -> Growth rate or intrinsic rate of natural increase
:
B
In the equation
$N_t=N_o{e}^{rt}$
$N_t$ is the population size at time $t$
$N_o$ is the initial population size at $t=0$,
$t$ is time
$r$ is the population growth rate per capita orintrinsic rate of natural increase.

Answer: Option D. -> Both statements are incorrect
:
D
Small animals have a larger surface area to volume ratio, this means a higher surface area to lose body heat, therefore these animals lose body heat very fast when it is cold outside and must expend metabolic energy to maintain body heat.

Answer: Option C. -> Sunlight, temperature, precipitation, water and soil 
:
C
Ecosystem comprises of two major factors i.e., biotic and abiotic. Abiotic factors are the non-living components which include sunlight, temperature, precipitation, water or humidity and soil. Living components like plants, animals, microorganisms like bacteria and fungi are the biotic components of an ecosystem.