The votes cast for the first past the post constituency election and the regional list are completely independent of each other. Voting for a Conservative first part the post candidate does not mean that you cannot vote for the Conservative regional list but nor does it require you to do so. However, if you wish to see the strongest possible Conservative presence in the next Scottish Parliament then it is vital that you cast BOTH your votes for Scottish Conservative candidates.
The only impact that the vote for the first past the post candidate has on election to the regional list is that in order to determine which party will see its top ranked regional list candidate elected to Holyrood first the total number of votes each of the parties secures for its regional list is divided by the number of first past the post candidates it has won in that region plus one. Whichever party has the highest number of votes once this division has been carried out sees its top ranked regional list candidate elected. In order to determine the second regional list MSP the exercise is then repeated with the only difference being that the party that has just gained a regional list MSP now has one more MSP and its regional list vote is divided by its number of first past the post MSPs, plus the first regional list MSP, plus one. This process is repeated until all 7 list MSPs have been chosen.
One of the consequences of this system is that it is more difficult for a party that has done well in securing first past the post constituencies in a region to win further regional list seats, and that in order to do so it is very important for it ensure that all its supporters cast their second votes for its regional list as well as their first votes for its constituency candidates. Please be sure to do so on 5th May 2016.