You can go below the plant level in searching for signs of awareness. I remember reading some interesting material in Stuart Kauffman's Reinventing the Sacred, which I read a few years ago. I will look through it and see if I can find a few relevant quotes.
I wasn't able to find "a few relevant quotes." The entirety of one chapter might do, but I can't find the book right now and I don't remember the name of the chapter (it might have been something like "The Origin of Life").
In the mean time I have been reading other books, starting with Sync
by Steven Strogatz (mentioned above) and now Linked
by Albert-Laszlo Barabasi, which is mentioned within Sync
(which also mentions Kauffman -- small world). They both deal with "small world" self-organizing networks (a.k.a. "scale free" networks), which can be found across the range of densities, and in which any node can be reached by traversing a relatively small number of intermediate nodes, irrespective of network size.
It would appear that "networking" is a fundamental aspect of our reality. Networks form even in 1st density, order themselves, and undergo "phase transition" to create systems that could not be anticipated if the results hadn't been seen before.
At this point, 1st density organisms "sensing each other" does not surprise me at all. We are just beginning to understand how things are really put together, and a lot of what we think we do that is special very possibly is not.