The best replacement for ecosystems is biomes.

The best alternatives to ecosystems are rated as following:

★★★★★	biomes
★★	habitats
★	ecology
	terrestrial ecosystems

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Speaking about ecosystems, one probably shouldn't forget about high net primary productivity.

Other search terms related to ecosystems and their ratings are:

★★★★★	high net primary productivity
★	biodiversity

You have in mind a companion for ecosystems and it is not yet here? Propose!

Google Trends

Scale is based on the average worldwide traffic of ecosystems in all years. Click on graph for more.

ecosystems

biomes

habitats