What do composers and scavengershave in common?

I'm going to assume that was 'decomposers'

Scavengers:

Eat dead animals or carrion. Break down organic material.

Decomposers:

Eat said organic material and breaks them down into chemical parts

Similarity:

Both are vital for keeping the ecosystem clean and preventing buildup of dead organisms.

Hope this helps!

1. is geographic distribution

2 is increasing complexity

3 is transitional forms