Many RPG worlds seem to have a fauna and flora that is composed of the organisms found in our world with a more or less well thought out set of monsters added on.
I was wondering how to design a believable ecology suitable for a fantasy RPG world spanning a small continent with earth like conditions (large enough to have several different biomes, for example warm deserts, mountains, plains, temperate forests and taiga, the exact biomes are not that important).
I want the ecology to contain a subset of earth organisms as well as non earth organisms, some of which should be considered monsters.
How can I define such an ecology that appears to have evolved through evolution under the following constraints.
- Definition should fit in limited space, maybe about 50 book pages of easy to read text (should fit in an RPG book along other world information and rules)
- Only defining details that seems important to the human inhabitants (no need to include bacteria for example)
- The definition should show how the "food pyramid" works and avoid mysteries such that how some creatures would find something to eat given their habitat or other aspect of their definition
- The non earth organisms should in some way fit into the tree of life (but maybe a modified one for organisms that evolved to use magic to function)
- Habitats for organisms should be defined, on some resolution, maybe by climate zone in some cases and in great detail in others if that seems important
- The definition should include which organisms are deemed valuable, both wild and domesticated, and which is considered problems
- The earth organisms should not vastly outnumber non earth organisms in any ecological niche
- The whole thing should feel like it fits together not just a bunch of creatures bolted on an existing ecology
Hopefully the question is understandable, I am not interested in a specific instance of ecology but rather how to design an ecology for such a world in a way that looks like it fits together without going into excessive detail such that it becomes an project that is impossible to complete (or that no one bothers to read).
A final point to specify, I am mainly interested in answers that uses no magic to solve problems, if it was not a fantasy world I would have tagged it with hard-science.