I want to know the answer to the following question:
Whose earlier work did Nicholas Vavilov build upon?
All the background I'm provided with is that "The discipline of plant ecology was pioneered in the late 19th century by botanists such as Eugenius Warming, who produced the hypothesis that plants form communities, and his mentor and successor Christen C. Raunkiær whose system for describing plant life forms is still in use today.". Is that enough to answer the question?