In the southeastern United States, marshes are dominated by two species of smooth cordgrass; Spartina alterniflora dominates the seaward edge of the marsh, while Spartina patens dominates the high marsh. You work with researchers and determine that if S. patensis is removed from the high marsh, S. alterniflora will occupy all of the marsh, into the high marsh. If, however, S. alterniflora is removed from the seaward side of the marsh, S. patens will only grow a small portion further seaward, and it does not seem to tolerate being submerged for long periods during high tide. Which of the following is a conclusion you can draw based on this experiment?
1- S. alterniflora is prevented from colonizing the high marsh under normal growing conditions due to predation, resulting in a more seaward realized niche.
2- When S. alterniflora is removed, S. patens can grow in all areas of its fundamental niche, indicating that its distribution is limited by competition to a smaller realized niche.
3- The fundamental niche of S. alterniflora is expanded by its mutualistic relationship with S. patens.
4- When S. patensis is removed, S. alterniflora can grow in all areas of its fundamental niche, indicating that its distribution is limited by competition to a smaller realized niche.
5- The experiment indicates that S. alterflora is a superior competitor and that is why it is found on the seaward side of marshes.

In the given question, S. alterniflora grows in the seaward marsh whereas S. patensis grows in the high marsh. When S. alterniflora is removed, the S. patensis grows to a smaller portion whereas if S. patensis is removed, the S. alterniflora covers all the land.

This shows that although both are different species but they share a niche and the marsh land is the fundamental niche of the S. alterniflora as it can grow in all parts and therefore its distribution is limited by only a realised niche.

Thus, Option-4 is correct.