Complex sentence: Historically this main concentration of Mikea may have extended as far south as the Fiherenana River and as far north as the Mangoky River; another main cluster of Mikea live to the west and southwest of Lake Ihotry.
Split into simpler sentences: Historically this main concentration of Mikea may have extended as far south as the Fiherenana River and as far north as the Mangoky River. Another main cluster of Mikea live to the west and southwest of Lake Ihotry.