Science Daily is wrong. Burning through community members is not a decent approaching to keeping your community active. It’s the worst thing you can do. You only develop transient relationships at best and, eventually, you run out of fresh blood. It’s like a bad pyramid scheme.
The best indicator of an online community’s survival is how many active veterans you have. How many members have been participating for 5 years? A single active veteran is worth 100 newcomers, maybe a 1000.
Takes actions today that will develop active veterans three years from now. Spend more time responding to comments of veteran members, write official thank you notes, invite them to the staff party, add game mechanics in their profiles, mention old-timers by name in your community’s history, consider a ladder listing the oldest active members (you can’t game this).