Great! thank you. But doing the same search with google book for "ecological balances" we get more and more results, 54 against 11.100; what do you think about that. Could be both correct? "Balances of nature" was my first choice, but I've received many invites to change it. – Kiron – 2013-06-29T22:13:26.187

I would say both are correct, but I would also say that in general you are safe avoiding the plural form for the most part. It looks like I might be in a minority on that, however. – BobRodes – 2013-06-30T00:56:32.933

1I tried to answer the pluralization question you posed. As for which is better, I'd have to know more about how you're planning to use it: What is the context? Who is the audience? P.S. As for "many invites to change it" – do you mean from Bob? Or have others given you the same advice? (I'd count Bob's advice as "one" invite to change it, not "many.") – J.R. – 2013-06-30T01:25:21.817

We routinely speak of ecosystems in the plural, because it's often easy to envisage small self-contained units (plus we routinely create them, in research contexts). But balance of Nature is something of a "set phrase", and I personally would rather not pluralise it in that exact form. Natural balances, maybe I could live with.

Here's an Ngram. That said, to get the full picture, you'd need to examine each of the usages in context, because there's no way to know if the writers are using the terms in places where they would be interchangeable – there might be a reason one term is chosen over the other. – J.R. – 2013-06-30T08:30:25.807

The Ngram with singulars added shows that the singular form occurs an order of magnitude more often than the plural in either case. That said, I entirely agree with J.R.'s statement.

@BobRodes: There are lots of Ngrams we can study, including this one with the articles removed. They all seem to show a pre-1970 rise in popularity for ecological balance(s), but, as we both agree, that's only one piece of the puzzle, and the O.P. shouldn't decide based on Ngrams alone.

Yes, that's interesting. I remember discussing "ecology" as a rather new idea in 5th grade science back in the 60's. – BobRodes – 2013-06-30T15:50:44.390

I was referring to invites out of this forum. Very interesting the Ngram feature. I didn't know about that. I was wrong about 54 vs 11.100 google search results, it is 13.600 vs 11.100, anyway Ngram says it all. About the context I have said, to use as a title, since was the easiest way to answer, now I'll try to be more clear adding a comment to the question. Thank you to everybody – Kiron – 2013-06-30T15:54:10.827

Thank you, I can be agree with you that there could be only one if we consider the whole planet, universe, etc. but if we are talking about some "small" ecosystems? Could be better to use "natural equilibriums" or "natural equilibria"? – Kiron – 2013-06-29T16:27:40.473

In that particular case, I would use "ecological balance." An example would be "If you use a natural wastewater treatment system, avoid flushing chemicals down the toilet as it will upset the ecological balance of the system." – BobRodes – 2013-06-29T16:30:22.813

Also for "ecological balance", always in singular form? I mean in general, not in your example – Kiron – 2013-06-29T16:32:50.167

An interesting question. I think you would find people arguing both sides of this one: "I would like to compare the ecological balance of the two systems" vs. "I would like to compare the ecological balances of the two systems." I lean towards the latter, and have the feeling that each has a slightly different meaning. But certainly, it is correct to say "Discrete systems have discrete ecological balances," so it isn't ALWAYS in singular form. – BobRodes – 2013-06-29T16:39:33.097

ok, thank you, I get it... I was looking for a plural form of that to use as a title – Kiron – 2013-06-29T17:00:28.973

In a title, "Balances of Nature" would be interesting. It implies several possibilities, such as that there are differing views on what the balance of nature is, or that there are different microsystems that have separate balances. – BobRodes – 2013-06-29T17:09:00.743

But now I have changed it to "ecological balances"... I have to switch back? ;-) – Kiron – 2013-06-29T17:12:17.353

If it's a title of a book, "Balances of Nature" arouses more curiosity in my opinion. If it's the title of a scholarly article, "Ecological Balances" is less provocative. You decide. :) – BobRodes – 2013-06-29T17:19:00.197

This doesn't answer the question, though. Assuming one did have a valid reason for using the plural, how would it be pluralized? When writing the science fiction series, the author had to be careful to make the balances of nature seem realistic on each planet. – J.R. – 2013-06-29T21:50:36.463

@J.R. Fair enough; I could have answered the question more specifically before getting into my musings. – BobRodes – 2013-06-30T00:54:42.160

Thank you for your answer too and for having seen my context – Kiron – 2013-07-01T15:01:47.130