So far we have presented a rather static view of communities as groups of species residing in the same place at the same time. But communities are actually complex networks of species with connections that vary in their strength (i.e., magnitude) and direction (i.e., positive, negative, or neutral). Every species in a community experiences multiple direct and indirect interactions.
focus your learning
Indirect interactions involving three or more species can affect species diversity and abundance in communities.
Keystone, foundation, and ecosystem engineering species have major effects on community structure.
The role of chance in maintaining community structure is poorly understood, but lottery, or neutral, models may help explain it.