Well....the fact that the ecosystem functions as one unit is enough reason to hypothesize that there is some sort of a common consciousness.
To exactly the same extent that a river maintaining a fixed depth is evidence of a 'common consciousness' - there are a range of feedback loops within natural systems, that the organisms within the ecosystem have evolved to supplement, that create that balance, but there is no evidence of, or need for, a common consciousness to explain it.
In fact, even what is generally claimed as 'Natural Selection' is a reason to suspect some sort of a coordinating intelligence.
If you think that, I don't think you understand 'natural selection'. Shorter animals die out, leaving taller animals to reproduce leading to a gradual increase in the average height of a populace doesn't lead to the conclusion 'therefore there must be a hivemind'.
Attributing everything to random and chance factors is such a...... cop out!
A cop out of what? How is making up possibilities for which there is no evidence because you don't like the answer 'natural selection of random variation within species' not a cop out?
If we can hypothesize that a strange thing such as Dark Matter exists everywhere, due to some mathematically calculated mass of all matter in the universe.....I don't see why a common consciousness is so improbable and 'out of this world'!!!
The answer is right there in your question. We hypothesize dark matter (and dark energy) BECAUSE we have a disparity between what we can account for with our current understanding, and our mathematical calculations of how that should behave: our current model doesn't match up to the evidence, so we need to hypothesise what might account for the difference. It is not impossible that there is a common consciousness, but that's not the benchmark that we're setting. It's not enough for it not to be impossible, there has to be a reason to accept that it's likely or evidenced; there is no need for common consciousness to explain the available phenomena, no need to explain something that isn't currently accounted for in the models.
It may, at some point in the future, transpire that there always was a common consciousness and that someone will find a way to demonstrate it, but for now it's exactly as well evidenced as Cthulhu, Gandalf and Darth Vader, and so it's accepted as a reality to exactly the same extent.
O.
O.