Bogs are another type of peat-accumulating wetland, but they only receive very small inputs of nutrients and alkalinity, entirely from atmospheric deposition associated with rain, snow, and particulates (that is, bogs are ombrotrophic, or "fed from the clouds"). As a result of their nutrient-poor status, bogs are highly unproductive and acidic, with a pH less than about 4.5 and as low as 3.5. The surface of the most ombrotrophic bogs is often raised above the level of the surrounding terrain, occurring as blanket- or raised-bogs, which can have peat depths of more than 30-50 ft (10-15 m). The vegetation of bogs is typically dominated by acid-loving species of peat-moss (these are known as acidophilous species, and they are different Sphagnum spp. than the ones found in fens), along with various shrub species in the heath family (Ericaceae). Because they are so acidic and unproductive, not many animals breed in bogs or their associated, brown-water pools.