The island of Hawaii is the youngest, and the islands get progressively older to the northwest. Plate tectonic theory explains this as

Answerinflux;

The oceanic islands primarily support themselves by living off the sea, that is through fishery, transporting goods across the sea and any other such activity that can provide for the families.

The most biodiversity is found on the ground, because here small plants, shrubs, big plants and trees grow, and when plants/trees die the branches/leaves are broken down by different insects and bugs which adds nutrients to the forest floor, therefore an area of great biodiversity.