Vagabond1066

All because you have that many, doesn't mean you require that many. Most of the strains of bacteria are in competition with one another. How many of those species could be removed and thier purpose still be fullfilled? Most of the species on Earth are window dressing, they could be removed and the ecosystem would still function. They aren't vital to the overall operation of the ecosystem.

Let's reframe the question. Say that life isn't common in the universe, but that it's extremely rare. Now let's say that we find an Earth like planet orbiting within the habitablezone of a Sun like star and it's completely lifeless. That for whatever reason, life never developed on it. How many species would be required to create a bare bones ecosystem capable of supporting Human life? Could it be done with 1,000 species? 2,000? 5,000?