The vast majority of animals and nearly all plants cannot maintain a constant internal environment. What is this called?

Community is:
$I.$ Group of independent,interacting populations of same species
$II.$ Group of independent and interacting populations of same species in specific area
$III.$ Group of independent interacting populations of different species in a specific area
$IV.$ Group of independent and interacting populations of different species in different area
Select the correct option.

Which of the following are the dominant plants of the cold desert?

Read the following statements and select the option that represents the correct statements.
$(1)$ Kangaroo rats never drink water.
$(2)$ Birds undergo hibernation to escape adverse environmental conditions.
$(3)$ Thermal adaptation can be explained by Allen's Rule.
$(4)$ Opuntia possesses phylloclade for protection.

Identify the organism based on the following characteristics:
- It has the ability to concentrate its urine.
- It meets its water requirements from internal fat oxidation.
- It is found in the American desert.

In colloquial language,habitat is a postal address while niche is the . . . . . . of the organism.