Across
- 2. light
- 8. species largely depend on
- 10. relating to earth
- 12. no sunlight
- 14. cold
- 16. harmful effect
- 17. warming hot earth
- 18. species invade
- 19. classified
- 20. salt freshwater
Down
- 1. group of people
- 3. harmful substance
- 4. species' first colonizers
- 5. trees
- 6. combined food chains
- 7. species nowhere else
- 9. too many people
- 11. symbiotic relationship
- 13. variety
- 15. biome water