Which situation will most likely cause the sustainability of an ecosystem to weaken?

A zebra is killed and eaten by a lion.
A disease wipes out several plant species.
A frog lays hundreds of eggs that hatch into tadpoles.
A dry season causes a few small trees to die.

Consider a culture medium on which only gram-positive organisms such as staphylococcus aureus colonies can grow due to an elevated nacl level. a yellow halo surrounds the growth, indicating the bacterium fermented a sugar in the medium, decreasing the ph as a result and changing the color of a ph indicator chemical. this type of medium would be referred to as a differential and enrichment culture.