Every once in a while, a week will come along in which Facebook app growth inexplicably falls by half or more. That’s the case on this week’s list of fastest-gaining Facebook games by monthly-active users, but there are still several trends that we can dig out.

The most notable is that Treasure Isle and Hotel City both seem to be heading for a plateau. Zynga’s Isle had already begun slowing by the time we wrote last week that it had passed Mafia Wars. It will likely become a bit larger over the next couple weeks, but very few apps have ever topped the 30 million MAU mark by much, with FarmVille being the notable exception.

As for Hotel City, the evidence that it’s leveling off isn’t as certain. But it, too is crossing a threshold. Aside from Isle, the previous top-growing game of the year was Social City, which appears to have maxed out around 12.5 million players.

Here’s our AppData top 20 list for the past week:

	Name	MAU	Gain	Gain, %
1.	Treasure Isle	25,608,814	+3,811,925	+17.49
2.	Hotel City	13,201,385	+1,542,779	+13.23
3.	Family Feud	3,652,686	+749,842	+25.83
4.	Mall World	1,999,058	+564,252	+39.33
5.	Tiki Resort	6,246,592	+403,685	+6.91
6.	Kingdoms of Camelot	2,451,248	+364,423	+17.46
7.	Zoo Paradise	4,738,486	+258,281	+5.76
8.	Battle Punks	561,586	+252,674	+81.79
9.	Bola	1,719,409	+200,109	+13.17
10.	Fish Friends	1,152,393	+144,074	+14.29
11.	Big City Life	367,489	+141,816	+62.84
12.	Jungle Life	138,730	+132,061	+1,980.22
13.	Name Analyzer	1,262,746	+125,928	+11.08
14.	Nightclub City	170,015	+105,768	+164.63
15.	My Tribe	541,987	+103,143	+23.50
16.	TransForce – Robot strategy browser game of 2010	248,573	+94,783	+61.63
17.	NanoStar Siege	221,334	+92,794	+72.19
18.	( Fupa Games ) – Arcade Blitz	247,843	+91,528	+58.55
19.	Bubble Popp	1,318,877	+85,086	+6.90
20.	¡Teclas Machucadas!	463,211	+83,540	+22.00

Family Feud and Mall World, at numbers three and four, show less evidence of a decline. Feud’s gain is only a couple hundred thousand MAU lower than the week before. As for Mall World, the girly-girl shopping game is still in the prime of its growth, and from here we expect it to pick up a couple million more MAUs.

Playdom’s Tiki Resort is that company’s dark horse, showing a longer and steadier growth trajectory than most other games we see; it has been headed up since its late February release. Underneath Tiki, our list heads into newer-growth territory, even if all the games themselves aren’t new: that list includes Kingdoms of Camelot, Battle Punks, Bola and My Tribe, as well as several others.

And because growth was so low overall for the past week — averaging about exactly half of growth on the previous week — with titles like Bubble Island and Garden Life having dropped off entirely, there are some brand-new games that have also broken in. Big City Life is another Playdom title, just released, while Nightclub City is a spiritual cousin by an independent developer; we’ve reviewed both, here and here.

Jungle Life, meanwhile, is from Metrogames, which Playdom has a $5 million investment in. We’ll cover it in more depth later this week, but the basic idea is that it’s yet another animal-collecting game, this time set in a jungle.