Hi,
I think that you're missing some options, but here they are (let me know if I'm right!
-A population of wolves was introduced
-The amount of disease in the deer population decreased
-More grass was planted
Now, if the gene diversity decreased, it means that a lot of deer died. This could happen because wolves were introduced -this is the correct answer, and the wolves ate some deer.
Mitosis
Mitosis is the part of the cell cycle in which the duplicated genetic material (chromosomes) within the parent’s cell nucleus is separated to produce two daughter cells that are genetically identical to the parent. Mitosis is important to life because it is involved in the production of new cells for growth and to replace damaged cells. Mitosis occurs in five stages which are; interphase, prophase, metaphase, anaphase and telophase (cytokinesis).