America Online is staking out its turf.

Monday's

plan to sink $100 million into

Amazon.com

(AMZN) - Get Amazon.com, Inc. Report

illustrates how the nation's biggest online service provider continues to expand its reach, though perhaps with a different strategy in mind.

The strategic shift at the AOL unit of

AOL Time Warner

(AOL)

is this, says one analyst: While past investments focused on capital appreciation, recent transactions seem to establish a claim on various technologies and services.

The Amazon investment, linked to an alliance in which Amazon will provide technology for

Shop@AOL

and other AOL shopping services, "marks AOL's territory," says Jordan Rohan, media analyst at

Wit SoundView

. "Amazon becomes a close partner of AOL," he says. Now, as a result, Amazon "really can't become a close partner of

Yahoo!

(YHOO)

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or a close partner of

Microsoft's

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MSN

to the same degree," Rohan says.

In that respect, Rohan says, the deal is similar to other investments and purchases the company has made in recent times. Since the January 2000 announcement of the deal to create AOL Time Warner, America Online's investments have ranged from a $200 million purchase of

TiVo

(TIVO) - Get TiVo Corp. Report

stock to participation in a $12 million venture investment in a Web content-recognition company.

Most of the investments appear to be related to new services AOL is developing related to shopping and new Internet technology.

In a recent article,

TheStreet.com

columnist Adam Lashinsky, for example, speculated that one recent AOL purchase suggested the company was muscling in on the voice mail services offered by local phone companies.

America Online didn't respond to a request for comment on the strategy behind its Amazon investment.

AOL's early investments, says Rohan, "had an eye toward real capital appreciation -- real liquidity value, getting out of an investment." (Rohan has a strong buy on AOL Time Warner and a hold on Yahoo!; his firm has a strong buy on Microsoft and a buy on Amazon. Wit SoundView hasn't done underwriting for any of these firms.)

But recent investments seem "a little more protective in nature," the analyst says: "'Let's make sure that no other portal or ISP cements a relationship with this company in an integrated fashion.'"

Just like in the animal kingdom: The biggest member of the pack always keeps a vigilant defense of its territory.