Is there any convention of how to express different types of relations (e.g., eats, turns into, is beneficial to) and agents (e.g., species, nutrient) in an ecological diagram? I know that inhibitory relationships are indicated by barred arrows, but I failed to find anything going beyond this.
Suppose, I want to express that Species A excretes Nutrient X, which in turn is metabolised by Species B. Naïvely, I would sketch this as follows:
However, this it not necessarily clear:
I here arbitrarily used squares and circles to distinguish species and nutrients. If you do not know this, you could not immediately distinguish them. (Of course, I may just use specific examples like tree instead of A, but then for my theoretical cases, a tree is too concrete.)
The arrows mean different things. The left arrow means excretes, the right arrow means is metabolised by. Moreover, the arrows could be mistaken for something like turns into or a general is beneficial to.
How would I denote the above relation unambiguously in a diagram?