An ecosystem that is not sustainable can break down when a natural diaster occurs. This can lead to organisms in the ecosystem either leaving the area or dying off. Increased biodiversity results in a more substainable ecosystem because-

a there are fewer species to be affected by environmental stresses
b a greater variety of species present allows more organisms to adapt after changes occur
c the transition are between two ecosystems in narrower
d a greater number of plants species means that there is less barren land