According to Tristan Garcia each thing is constituted by the relation between that-which-is-in-the-thing and that-in-which-the-thing is. That is to say, each thing is constituted by the relation between its components and its environment. But then things are partially constituted by their environment. From this is follows that a first cause cannot exist. For, a first cause is the (in)direct cause of its environment and therefore not partially constituted by it.
Markus Gabriel has it that to exist is to exist in a context. This entails as well that a first cause does not exist. For if there is a first cause, it exists in some context. This context is caused by the first cause. At the same time the context must be ontologically prior to the first cause, since without this context the first cause doesn't exist. But this is impossible, since nothing is ontologically prior to its cause.
Are Garcia's and Gabriel's ontological claims about the nature of thinghood convincing? If so, interesting arguments from speculative realism against the existence of a first cause are obtained. It seems to me though that both ontologies face serious problems. Some of these I have disucssed elsewhere. And I will continue to do so.