In order to get a good idea of who you would work with as an ergonomist or usability professional, you need to understand how and why different professionals are brought together in the first place.
To help you do so, this site discusses collaboration on seven different levels, frequently referring to Canadian examples:
One-on-one: how any given professional might collaborate with another
Within a Single Organization: how professionals interact within an ergonomics or usability association, and how such associations are usually structured
Multi-organizational: how professionals in one association work with professionals in another association, and the unification of several associations under a common goal.
National Collaboration: how organizations are affiliated at a national level; what efforts have been made to guide various countries, and what this signifies for individuals
International Collaboration: how ergonomics and usability has been organized inter-nationally, and how they accomplish worldwide standards.
Consultant-Client Relationship: a brief description of participatory ergonomics and how it helps consultants encourage user-centered design at client companies.
Researchers & practitioners: a look at how academic professionals both inform and differ from practicing professionals, and how the practical nature of ergonomics can get between them.