Different yarn can have the same gauge, which means they are just as thick or thin, and gives exactly the same amount of stitches in width and rows in height.
Yarn with the same gauge can be used on the same pattern.
Yarn with the same gauge, may have different yardage due to different weight of the fiber. When using an alterntive yarn, it's important to calculate the yardage needed.
Original pattern is using 500 g Alpaca. 500 g = 10 skeins.
Each Alpaca skein has 182 yards, so 1820 yards are needed for this pattern.
Let's use alternative yarn Cotton Viscose, which has 120 yds per skein.
1820 divided by 120 = 15.17. If using Cotton Viscose you will need 16 skeins.
Pattern DROPS 115-14 uses DROPS MerinoExtraFine. Here is a list over alternative yarns for this quality: