While Causal Efficacy is rather popular as a criterion of existence, it is rarely noticed that there is a closely connected criterion which is quite as plausible, which we call 'Causal Origination': 

Formulation:

An entity exists only if it has a causal origin (was caused).

It is an obvious further step to combine Causal Efficacy and Causal Origination--the result we call 'Causal Integration'.

Formulation:

An entity exists only if it has a causal origin and is causally efficacious.