I find this question a little ambiguous as there is very limited context around it. This would be my answer and pls note the context given after.
From the Primary Science, P6, syllabus we are taught the Food Chain as part of “Food Webs”. One lesson teaches us that when we "upset" / "change" the food chain, in this case remove a predator, the prey’s population will increase until a new natural balance is established. For example in this case the Zebra population will grow since there are a reduced number of predators. However, more Zebras will result in more plants / grass is being consumed. As a result, over time, the number of zebras will decrease a little (still more Zebras than when there was Lions around) as the supply of food (plants) is reduced on a per zebra basis. Eventually we reach a new balance between Zebras and plants.
Notes:
I have drawn the graph in this way to highlight an increase in the Zebra population and a decrease in the number of plants / amount of grass at the start with a new balance being established over time.
The choice of Lion and Zebra in this question is interesting. It is either trying to make a general assumption regarding the changing in the food chain or suggest that there would be minimal change given the 1 year time line and considering the Lion is not the main predator of the Zebra. See points below .
We do not know the size of the Zebra nor the plant population therefore I have arbitrarily chosen where to place the starting points along the Y-axis.
Of course looking at this question more holistically, there is more to consider – beyond P6 but still interesting.
Other animals rely on plants as a food source and thus the entire ecosystem of the Zebra’s habitat will change creating a new balance between plants and animals in general.
The Zebra’s main predator is not the lion, but instead man. There are more Zebras killed through poaching for their skin (leather) than by lions.
Lions typically attack the old, the young, the weak and the sick Zebras. As a result many of these Zebras would die naturally due to old age and/or disease reducing the impact of a reduced number of lions. In addition, a healthy strong adult Zebra can outrun and/or withstand a lion attack – see video below of the strength of a Zebra (some young kids may be disturb by the video).
Even if all hunting stopped and all lions were killed, the Zebra’s gestation period is roughly 350 to 400 days. Thus it will take much more than 1 year for there to be a noticeable change in the ecosystem. A more realistic change in the graph would have a slight increase in the Zebra population and a slight decrease in the amount of grass and plants through the first year. Over time there would be a growing population of Zebras and a decreasing amount of grass/plants. The reduction in grass/plants would result in less grasshoppers, etc. and other plant eating animals.
Finally, an increase in the Zebra population may result in an increase in the population of other Zebra predators such as hyenas, leopards, cheetahs, and/or wild dogs over time given there is an increase in the food source (i.e. Zebras).
