Complete the crossword, then click on "Check" to check your answer. If you are stuck, you can click on "Hint" to get a free letter. Click on a number in the grid to see the clue or clues for that number.

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Across: 2. An event, such as a fire or windstorm, that kills or damages some organisms in a community, thereby creating an opportunity for other organisms to become established. 5. (2 words, no space) An area on the side of a mountain facing away from moist prevailing winds where little rain or snow falls. 7. A distribution pattern in which organisms tend to be positioned in an unpredictable manner throughout the environment. 9. The variety of organisms on Earth or in a particular location, ranging from the genetic variation and behavioral diversity of individual organisms or species through the diversity of ecosystems. 10. All living organisms on Earth, together with the environments in which they live. 12. The prevailing weather conditions experienced in an area over relatively long periods of time (30 years or more). 15. A major terrestrial or aquatic life zone, defined either by its vegetation (terrestrial biomes) or by the physical characteristics of the environment (aquatic biomes). 17. A community of organisms, together with the physical environment in which the organisms live. 18. Temperature, precipitation, wind speed, humidity, cloud cover, and other physical conditions of the lower atmosphere at a specific place over a short period of time.

Down: 1. (two words, no space) A period during which large numbers of species become extinct throughout most of Earth. 2. The geographic area or range over which a species is found. 3. The scientific study of interactions between organisms and their environment. 4. The habitat in the branches of forest trees. 6. The mass of plant matter that a plot can produce from the available nutrients and sunlight. 8. An act in which individuals travel relatively long distances away from other members of their species. 11. A forest that receives high rainfall. 13. A distribution pattern in which organisms tend to be positioned in an even or uniform manner throughout the environment. 14. A characteristic place or type of environment in which an organism lives. 16. A distribution pattern in which organisms tend to be clustered together throughout the environment.