Step 1: Understand the term ‘Synecology’.
Synecology is a branch of ecology that deals with the study of groups of organisms and their interactions within a community rather than focusing on a single species. It emphasizes relationships among species living together in a habitat.
Step 2: Differentiate from autecology.
Autecology refers to the ecological study of an individual species, including its behavior, adaptations, and environment. Synecology is broader and focuses on multiple species forming ecological communities.
Step 3: Analyze option (1).
“Ecological study of individual species” corresponds to autecology, not synecology. Hence it is incorrect.
Step 4: Analyze option (2).
“Study of ecological communities” correctly defines synecology because it includes interactions between populations of different species.
Step 5: Analyze remaining options.
Plant ecology and physiological ecology are specialized branches and do not define synecology. Therefore, they are incorrect.
Step 6: Final conclusion.
Thus, synecology refers to:
\[
\boxed{\text{Study of ecological communities}}
\]