According to 10% law, 90% of energy is lost when it moves from trophic level to the next, the residual energy decreases drastically with 2-3 trophic levels. That is why a food chain in an ecosystem is generally limited to 3-4 trophic levels.

a) The reduction in tiger population may  result in the increase of prey population (deer ), since they are not preyed upon. and increase in number of deer leads to reduction in grass
b) After the introduction of tigers, balance in nature is expected to return.

Pyramid of energy is always erect. If the rate of reproduction of phytoplankton was slowed down ,it would cause a reduction in the number of trophic level ,because there would be very less energy available to sustain a particular level.

In primary succession on rock, pioneer species like lichens secrete acid which dissolve rocks helping in weathering and soil formation.

Due to change in the condition of soil, nutrients, environmental conditions, the communities specific to it also change.

Fragmentation done by detrivores like earthworms.
1. Due to ploughing detrivores exposed to their predators
2. Due to killing of detrivores , rate of fragmentation slows down.

Ultimate source of energy in both DFC & GFC is Sunlight.

Pyramid can not accommodate species belonging to two or more trophic levels.

Rest of the energy is liberated in the form of heat. 90% of the energy is used for growth and maintenance and rest 10% remains that is passed on.

Energy in an ecosystem flows from producers to primary consumers, then from primary consumers to secondary consumers and so on.There is never a backflow of energy, i.e., energy cannot come back to atrophic it has already passed.Therefore, the energy flow is unidirectional in an ecosystem.