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By the end of this decade, the battle between the Apple Watch and rival Android smartwatches will be a much tighter one.

That shift will come as consumers get more familiar with smart wearables, still a very new type of gadget for most people, and as those devices surge ahead of more basic wearables such as fitness trackers, market researcher International Data Corp. said in a forecast released Monday.

For 2015, IDC predicts a wide spread between the Apple and Android camps. The market-dominating Apple Watch and its WatchOS software this year should account for 13.9 million device shipments and a 58.3 percent share of consumers' acquisitions of smart wristwear. Android Wear, found on a variety of devices, including Motorola's Moto 360 and the LG Watch Urbane, will clock in at 4.1 million shipments and a 17.4 percent share.

By 2019, Apple's share will have dipped below the halfway point, to 47.4 percent on shipments of 40.3 million devices, IDC said. The Android side, meanwhile, will be up to 38.4 percent, riding shipments of 32.6 million units.

Other smart-wearables contenders are now and will remain well behind the leaders, according to IDC. Pebble, for instance, will see shipments rise only slightly in 2019, to 2.6 million units as its market share dips to 3 percent, while Samsung's Tizen will edge up to 1.8 million units for a 2.2 percent share.

Smartwatches have been around for several years but none managed to find more than a handful of buyers. The market perked up considerably toward the middle of this year with the arrival of the Apple Watch, the first wearable from the Mac and iPhone maker. The company itself has yet to say how many watches it has sold, but researcher Strategy Analytics reckoned that some 4 million Apple Watches had been shipped by the end of the second calendar quarter.

Other smartwatch makers have been busy in the last month or so. Samsung, for instance, unveiled the Gear S2, its seventh smartwatch but the first with a round watch face. Motorola revamped the Moto 360, the most successful Android Wear watch yet, into more of a fashion piece .

In addition, Google announced two weeks ago that Android Wear smartwatches now work with Apple's iPhones, which could be one of the things that helps drive consumer interest in devices that run the variant on the Android software for smartphones.

Part of what's kept smartwatches and smart bands from catching on, IDC said, is that they've tended to be yoked to a nearby smartphone. But that will change with new generations.

"Smart wearables will quickly move from a smartphone accessory primarily focused on notifications to a more advanced wearable computer capable of doing more processing on its own," said Jitesh Ubrani, a senior research analyst for IDC, in a statement.

What sets smart wearables apart from basic ones is that they can run third-party apps, and clearly there's been rapid growth on that front. Apple said last week that more than 10,000 apps have now been developed for the Apple Watch.

The growth in all wearable devices, smart and basic, will be vigorous over the next several years, IDC said. Shipments worldwide this year will total 76.1 million, more than two-and-a-half times as many devices as in 2014. By 2019, the number shipped will rise to 173.4 million units, for a five-year compound annual growth rate of just under 23 percent.

But smart wearables will be the pace-setters throughout the period as consumers overcome their initial hesitation. In 2018, according to IDC's forecast, those brainier devices will surpass their basic counterparts, which today account for about two-thirds of the market.