Is fiction more heavily influenced by other forms of prose, like the essay?Is fiction more heavily influenced by other forms of prose, like the essay?
Literature is influenced heavily by fiction in terms of reader numbers. Whether the most popular forms of fiction qualify as literature is another matter of opinion and always up for debate. For example the so-called 'chick-lit' genre of fiction which often includes novels and novellas about young working girls and their lives, loves and problems is very popular among young women today, yet many would ask 'is it art?' or 'is it literature?' or just 'chewing gum for the eyes' to be readily absorbed and forgotten by the masses. In contrast, essays and letters can be fascinating glimpses of a famous author's soul and are often more useful than biographies in this regard. yet they are not widely sought out by the general book-buying public. A novel like 'Bridget Jones' Diary' on the other hand is seen as very representative of today's issues - and books like these get made into movies, so having even further influence on society.
It's not that you can't find ways in which other forms of prose influence literature, it's that fiction is so vast and diverse in nature that any specific influence in modern publishing would be hard to spot, and subjective conjecture if you did.
In general, I would say that mass market fiction, popular fiction, is less influenced by any other formal writing, and more by conversational style and modern forms of interacting.