Evaluate the collective function of references cited together in a given text segment.
Classify their combined role into one of the following categories: 'method', 'background', or 'result'.

Text:In prairie and barrens, we categorized the species by habitat niche breadth (Swengel 1996, 1998b): (1) specialist (restricted or nearly so to herbaceous flora in prairie and/or savanna; sensitive to vegetative quality); (2) grassland species (widely inhabiting both native and degraded herbaceous‚Ä¶
Category: