Environmental dimensionality
For example: of a filamentous fungus in soil
So, what I am currently thinking about is this (triggered by some discussions during my visit at OIST in Okinawa): how many dimensions does the environment of an organism have? Put in another way: how many parameters does an organism at any one time sense, integrate and then react to?
In ecology, the first thing that comes to mind is the niche, famously defined as the “n-dimensional hyperspace”, and this is of course highly non-committal in terms of numbers. Even though, to be honest, I never thought about it until now. How big is the n, that is basically the question. Is it 5 or is it 500 or even 5000? How many variables can an organism (or a cell) perceive and somehow process at a given point in time and overall?
This is probably already a rather complicated question (even though maybe there is a mathematical solution). But for a fungus, it is maybe even more complicated. Why is that? Well, because a fungus is a microbe, meaning a hyphal tip will perceive a microscopic micro-environment perhaps not that much different from a bacterium, but the mycelium as a whole also manifests at a very macroscopic scale, think of fairy rings, for example. This means the answer to the question about dimensionality probably differs a lot if you’re talking about a single hyphal tip or the entire mycelium (or a part of it). That is because the answer to the question of environmental dimensionality generally will very likely strongly vary with scale and integration.
So how could you experimentally test this? I am not sure….any ideas?
Why does it matter? Well, that is clear to me: it seems that is a very fundamental question about life. Every living entity will have to deal with this, the multitude of environmental influences that matter for it, called its Umwelt (German for environment). I think it matters a lot, because it determines what we should measure. For a soil, we routinely measure a bunch of variables, like pH, temperature, water content, soil carbon, nitrogen, etc. But do these things matter if they are not limiting the growth (or otherwise performance) of a fungus? And how much of this information is integrated at the level of the organism or the cell? Does it matter if a fungus is being grazed by 5 species of collembola, or does it just perceive it as an amorphous ‘predator’ threat? How about different soil organic carbon molecules? How many of those are perceived as different entities somehow?
Haven’t read much about it, this is just an idea at the very initial stage. So if you know more about this, please share in the comments (or a DM). :)
I guess that effect size analyses must be applied to transcriptomics and metabolomics data at different integrative levels of samples of different completeness of the organism of interest and of its habitat, which must also be characterised by basic and integrative parameters after its factorial manipulation. - Challenging, indeed. - The larger, more complete the sample, the less mechanistic the insight will be, since drivers and responses will integrate over many things.
Really interesting question. I like the shift from counting environmental variables to asking how many of them an organism can actually perceive and respond to. Maybe the key is not the total number of variables, but the number of distinct responses they generate，if different cues trigger the same response, they may belong to the same effective dimension.