It's an uncontroversial understanding that the various elements of an ecosystem interact in a number of ways, but at no point have I come across anything that reliably supports the concept of a shared subconscious - all the interactions identified have definitive physical methodologies.
There have been people attempt to formulate scientific hypotheses about such things - Rupert Sheldrake springs immediately to mind - but I've never seen them proffer anything reliable in the way of evidence from solidly conducted studies to back it up. As such, it remains just one of any number of 'possibilities', but nothing more.
O.
The idea of a common consciousness is a ancient one from the days of the Vedanta 3000 years ago....maybe even earlier.
One of the reasons for this idea is the complexity of life and its interconnected nature. All physical activities will naturally have physical methods of intervention. We can see that even in our own lives, for example, when we see a child and feel a sense of love and joy...there is a physical component in terms of chemicals and hormones rushing in. But the trigger is the mind and the physical reaction is a consequence. Just because there is a physical component to every action or reaction does not mean it is entirely physical.
We will once get into an argument about the nature of the mind and the real nature of Consciousness.
Second is the sense of interconnectness that many people feel subjectively. This is something we can learn to experience by trying to eliminate the sense of individuality that we normally feel. The less the sense of individuality the more the sense of interconnectedness. That is why self centric mindsets are discouraged in spiritual practices.
Yes....as you say..a common consciousness is a possibility in terms of objective scientific research but in terms of personal acceptance it is a certainty for many people.