Complex sentence: Facilitation is a mechanism whereby certain species help or allow other species grow by modifying the environment in a way that is favorable to a co-occurring species (Vandermeer 1989).
Split into simpler sentences: Facilitation is a mechanism whereby certain species help other species grow. One definition of facilitation is a circumstance where a species modifies the environment in a way that is favorable to a co-occurring species (Vandermeer 1989).