Network reciprocity, direct reciprocity, and indirect reciprocity are widely recognized mechanisms for the emergence of cooperation, but hardly verified in real-world environments, especially because they coexist. With a unique data set from online societies, we are able to extract measurements of cooperation mechanisms from social ties and of cooperation strength from cooperative activities, which allow us to uncover their causality relationships with econometric models. Our results highlight the great importance of social network on promoting cooperation. However, when social connections are absent, the cooperation encouraging effect dramatically shrinks for upstream indirect reciprocity and disappears for downstream indirect reciprocity, indicating that social network is a pivotal factor to transmit gratitude and build reputation. Our results not only deepen our understanding on the simultaneous effects of multiple mechanisms on the evolution of cooperation, but also provide a new research framework for empirically detecting the causal factors of cooperative actions in real worlds.