Plants Are Not Alone - The social networks of plants are pervasive and profound. Plants participate in communities that include beneficial and pathogenic microorganisms, beneficial and herbivorous animals, other plants, and humans. Stable relationships between plants and their partners that have been established for millions of generations are now under threat by global changes arising 
from human activities. This lecture gives an overview of the major types of plant biotic interactions, each of which will be explored in more depth in subsequent lectures. First published June 16, 2011, revised by William E. Williams ( April 2, 2013.