Which of the following ecosystems is both man-made and aquatic?

Consider the following statements concerning food chains.
$I$. Removal of $80\; \%$ tigers from an area resulted in greatly increased growth of vegetation.
$II.$ Removal of most of the carnivores resulted in an increased population of deers.
$III.$ The length of food chains is generally limited to $3$ to $4$ trophic levels due to energy loss.
$IV.$ The length of food chains may vary from $2$ to $8$ trophic levels.
Which two of the above statements are correct?

Given below are two statements:
Statement $I$: In an ecosystem,there is a unidirectional flow of energy from the sun through producers to consumers.
Statement $II$: Ecosystems are exempted from the $2^{nd}$ law of thermodynamics.
In the light of the above statements,choose the most appropriate answer from the options given below:

$A$ snake feeds on a rat,a hawk feeds on the snake,and the rat feeds on a grasshopper. In this food chain,what is the trophic level of the rat?

According to $David \ Tilman$,greater the diversity,greater is the primary productivity. Can you think of a very low diversity man-made ecosystem that has high productivity?

From the above given features,how many are associated with primary succession?
Features:
$1$. Occur on newly cooled lava
$2$. Faster succession
$3$. Progress to mesic condition
$4$. Occurs on flooded land
$5$. Slower succession
$6$. Changes in flora only