what would happen is all producers are killed by a loss of fertility of the soil or toxic contamination?

Question

what would happen to an ecosystem

Answer 1

Well it would certainly take a lot to do that. Because of variation it is very likely that some kind of producer would be able to exploit the new type of habitat and lack of competition. Under this situation the population model would follow that of most cataclysms. Species that currently live at the margins would all of a sudden find themselves dominant because the median would shift drastically. Also life forms linked to the species that died would die out, while those that could exploit the new dominant species would flourish.

However in your little scenario it is very unlikely that anything could kill all the producers without also killing other forms of life. Those that could survive would pretty much all die barring mutation allowing them to produce.

Answer 2

I'll make this nice and short. If all producers are killed, no more energy enters the ecosystem. Then, the animals higher onto the foodweb die because they don't have anything to eat, so the ones that eat them die, and then the ones that eat those die....and so on.
So if all producers in an ecosystem died, then all life in the area would die (besides some bacteria, would would probably live for a while, but if no more energy is introduced they too will die), but it is highly unlikely for all producers to die

Answer 3

If everything in the ecosystem is killed by loss of fertility, then there no longer an ecosystem to worry about. It's Dead.