Only to humans. Wrigglers do quite well in non-maintained pools. So do tadpoles. So does algae. Niches weren't created for you; you just found your niche.
Wondering if a pool without maintenance would last 10 yrs, 100 yrs, 1000 yrs, 100,000 yrs, 1,000,000 yrs, 1,000,000,000 yrs?
Niches are subject to disapperance in short periods of time. Consider the number of recorded extinctions in our lifetimes. "Nature" has her work cut out for her!
The ratio of new life forms to extinct life forms is BAFFLING!