Consider the following statements and choose the correct answer:
1. The effects of biotic factors include interactions amongst plants growing in a community, between plants and animals including man and between plants and soil-microorganisms
2. In a densly populated area, one of the most important types of biotic factors influencing vegetation is due to man's multifarious activities - this is noted in farming operations
3. Change or destruction of vegetation by fire is a direct biotic effect due to man's activities
4. In many cases different plant groups, plants and bacteria live in mutual benefit - this is called symbiosis in which each partner derives some benefit from the other