Ecology

SM Stirling, The Scourge Of God (New York, 2009), Chapter Eighteen, pp. 429-430.

Tens of thousands of bison graze;

they stir up insects;

birds fly about the bisons' feet to catch the insects;

wolves follow, hoping to catch a calf;

the wolves sheer off as mounted human beings approach;

eagles fly above, hoping for something bigger to be flushed by the herd.

Here, at least nine species interact:

grass;
bison;
insects;
small birds;
wolves;
human beings;
horses;
eagles;
whatever the eagles swoop on.

It is good to read a narrative that makes us aware of interacting species, not just human beings. When Poul Anderson imagines a planet, he has to create its ecology ex nihilo.