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No, the two systems operate separately. I would let this ride out a bit longer before you jump to too many conclusions. There are many variables that could have influenced this situation such as new competitors entering the PLA's, a slight algo update wasn't in favor of your site, or seasonality depending on what you are selling. A mix of good organic rankings and PLA's/PPC usually has a 1+1=3 effect because you have more "real estate" on the web, hopefully on the first page.