Complex sentence: Their rather large and increasing number for a place like Gir Forest National Park means that the sanctuary's area is now insufficient to sustain them, and that lions have moved outside the protected area, making them a potential threat to humans even outside the park.
Split into simpler sentences: Their rather large and increasing number for a place like Gir Forest National Park means that the sanctuary's area is now insufficient to sustain them. Consequently, lions have moved outside, making them a potential threat to humans even outside the park.