Is the soft parts of organisms more likely to become fossils?

NO.
the bones are fossiled because sometimes they contain the radioactive isotope  C14 

Competition. interaction among organisms that compete for the same natural resource (food, shelter, water, space) in an ecosystem. predation. an interaction in which one organism kills another for food. predator. prey. symbiosis. mutualisum. commensalisum. parasitisum.

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