What type of organism would most likely be found in place of the question marks?

Decomposers

Explanation:

The diagram in this question illustrates a food web, which is a series of interlinked food chains in an ecosystem. In a food chain as depicted in the image, the arrows point to the organism that feeds on another organism. For example, an arrow is pointing from Idaho fescue to an Elk meaning that the elk will feed on that plant.

Different trophic levels constituting organisms exists in the food web including; producers (plants), primary consumers, secondary consumers, tertiary consumers etc. However, as observed in the image, a general arrow carrying along all the organism is pointing towards the organism in the question mark. This organism is called DECOMPOSER.

A decomposer, usually a microorganism, is an organism that breaks down dead organisms and returns the nutrient to the soil for recycling. All organisms in the food web will eventually die and when they do, they'll be decomposed by a decomposer. This is why the arrow pointing towards the decomposers include all organisms.