Why are pioneer species usually autotrophs? A. Newly established ecosystems do not usually have pre-existing food sources.

B. Only autotrophs are large enough to survive.

C. Autotrophs are usually at the top of an ecosystem's food chain.

D. Only autotrophs can survive where water is scarce.

 Newly established ecosystems do not usually have per-existing food sources. ... An exotic insect is introduced to a forest ecosystem. It is resistant to the toxins the trees produce to protect them from being eaten by insects.

Explanation:

supercell thunderstorms are perhaps the most violent of all thunderstorm types, and are capable of producing damaging winds, large hail, and weak-to-violent tornadoes

oxygen = 21% of the atmosphere

nitrogen = 78%

carbon dioxide = 0.1%

argon =0.934%