• by Erik Sass , Staff Writer @eriksass1, March 25, 2013

If the headline sounds like an episode from “Game of Thrones,” that’s on purpose: the spectacular rise and fall of Orkut, Google’s social network in Brazil, is nothing if not epic.

Once upon a time, and not that long ago, Orkut was far and away the most popular social network in Brazil: in September 2008, comScore calculated that of some 26.2 million Brazilians with Internet access, 20.8 million were active members of Orkut, equaling 79% of the Brazilian Internet population. That compared to just 3.9 million for Yahoo’s Geocities and smaller numbers for a variety of other social networks; Facebook was way down the list with just 360,000 unique visitors in September 2008.

Since then, the Brazilian Internet population has soared to over 88 million, but that increase hasn’t benefited Orkut -- quite the opposite. As in the U.S., Facebook’s rise in Brazil was meteoric, jumping 192% from 12.4 million in December 2010 to 36.1 million in December 2011, when it finally surpassed Orkut. Over the same period, Orkut had increased 5%, from 32.3 million to 34.4 million, and the declines began soon thereafter.

Now in February 2013, according to Hitwise, Facebook was the most popular social network, visited by 65% of the Brazilian Internet population, followed by YouTube with an 18.5% share. Orkut had fallen to a distant third with a paltry 3% share of the Internet audience, down from 28.2% in February 2012.

While all this certainly appears to be good news for Facebook, as another country falls to unstoppable Big Blue, there’s another way of looking at it, which is much more ominous for Facebook. Above all, the fall of Orkut provides yet more proof that a large, active user base is no guarantee of continued popularity or longevity. This suggests that Facebook, despite its current ubiquity, is still vulnerable to up-and-coming networks like Tumblr, Pinterest, and Pheed, to name just a few.

The model for Facebook’s decline is already there, not just in Orkut, but in Friendster and MySpace as well. The recent Friendster “post mortem,” much publicized on the Web, documented how a loss of interest and disengagement by some users can trigger a rapid cascade of similar behaviors in their friends, leading to a general exodus in a remarkably short period of time.

In this vein, it’s worth noting data from SocialBakers seeming to show that Facebook’s user base in the U.S. has fallen from 170 million at the end of December to 163 million in recent weeks. Admittedly that’s just 4.1% of the total user base, and the network has experienced monthly and seasonal fluctuations before. But as Facebook rolls out yet another in a long series of redesigns, it is food for thought.