Final answer:
The Carpathian Mountains cover southern Poland and extend into the Czech Republic, Slovakia, and Ukraine, forming a significant natural barrier and influencing the region's climate and ecology.
Step-by-step explanation:
The mountain range that covers southern Poland and extends into the Czech Republic, Slovakia, and Ukraine is the Carpathian Mountains. This extensive mountain range forms a natural barrier separating different geographical and cultural regions in Central and Eastern Europe. Famous for their scenic beauty and biodiversity, the Carpathian Mountains also play a significant role in the climate and ecology of the regions they span.