The nature and scale of ecosystem functions, such as carbon-fixation a
nd nutrient cycling in a freshwater pond, appear to be governed by com
plex reciprocal interactions involving physical, chemical and microbio
logical Factors. Moreover, these interactions continuously create new
microbial niches that are quickly filled from the resident pool of rar
e and 'cryptic' (and probably cosmopolitan) microbial species. This co
uld mean that microbial activity and diversity are both a part of, and
inseparable from, pond ecosystem function, and that concepts such as
'redundancy' of microbial species, and the 'value' of conserving biodi
versity at the microbial level have little meaning.