.
The nature of the organism does not apply here; that is a question for the use of the 's genitive vs the of-genitive (the girl's feet vs the feet of the table)
205,000 for "investor funds"
209,000 for "investors funds"
209,000 for "investors' funds".
6,230 for "investor's funds"
Obviously, Ms Google does not discriminate between "-rs" and "-rs' "... and probably confuses the other premutations somewhat as well. The fourth option should be reserved when speaking of a single investor, but I think that the other 3 options are all valid for general purposes.
Investor funds-- investor is an adjective describing the funds
Investors funds-- as above, but plural (which is not the usual way we do it: it's shoe store, not shoes store.. but on the other hand sportswear)
Investors' funds-- the funds belong to the investors.