The fact that so many people wanted Apollo stock yesterday is what makes today’s drop so surprising. Companies with oversubscribed IPOs often choose to leave some prospective buyers wanting more, in order to spark a first-day pop. Perhaps Apollo filled all of its purchase orders, leaving only sellers today. Or maybe there were some broader forces working against alternative asset managers, as rivals like The Blackstone Group (BX), Kohlberg Kravis Roberts & Co. (KKR) and Fortress Investment Group (FIG) all lost ground.

One argument I’ve heard is that Apollo may be one publicly-traded private equity firm too many, and that public market investors are worried about a niche market becoming saturated. The problem with that line, of course, is that Apollo had people knocking down its doors to buy at the IPO price of $19 per share. Moreover, some market sources believe that additional PE firm flotations will lift all issuers, because they will lead to more sector analysts and (hopefully) understanding.

Moreover, there are significant differences between firms like Apollo and Blackstone, even though both fall under the same general classification. For example, Apollo has been better known for its debt investments lately than its equity ones (seems to be one firm that grabbed the knife near its nadir).

But there must be at least some mild concern at firms like The Carlyle Group, which has spent the past year in private discussions about filing for an IPO (may have gotten held up by a CFO switch). Expect them, and others like TPG Capital and Oaktree Capital Management, to pay close attention to Apollo’s performance over the next several weeks and months.