Biodiversity is an indicator of the health of an ecosystem because the more biodiverse it is, the healthier it will remain. As organisms become endangered or extinct, links in the food webs in those areas are compromised. The niche that these organisms play in nature won't be fulfilled and the entire system can be in jeopardy. That said, due to habitat destruction, acid deposition, global warming, pollution, depleting the fishing stocks, introduction of exotic species and others, biodiversity in many places all over the world is being threatened. If humans can live sustainably on Earth without devasting resources and the environment we live in, biodiversity can thrive. Biodiversity supports ecological services including, purification of the water and air, pollination, prevention of erosion and the stabilization of CO2 levels. Therefore, it is to our advantage to protect biodiversity on Earth.
Biodiversity is the sum of the variety of organisms (living things) in the biosphere. If an ecosystem can support many different living things it is a sign that the ecosystem is balanced with each of the organisms filling a specific niche. Often when organisms show signs of stress (mutations or decrease in population) it means that the ecosystem is not doing well. There could be many reasons for this: carrying capacity, invasive species, density independent factors (flood, drought, forest fire), or even man made causes like pollution, habitat destruction and over hunting/ gathering.