It’s now been a full week since Instagram added video recording to its popular camera app, and it’s already had a dramatic impact on its main competitor: Vine sharing on Twitter has tanked. We can use Topsy’s free analytics tool to compare how many times Twitter users have shared instagram.com links versus vine.co links, and the chart isn’t pretty for Vine. Vine sharing went into a nosedive on June 20, the day of Instagram’s announcement. Topsy shows there were almost 2.5 million Vine links shared on June 19, then a little more than 1.5 million on the 20th — a drop of almost 40 percent in one day. Vine sharing on Twitter has continued to drop over the week since Instagram video rolled out. Yesterday saw less than 900,000 Vine links shared on Twitter — that’s about a 70 percent drop from the nearly three million links that were shared on June 15th.