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:Streptomyces are well known for their prolific production of antibiotics, which are
thought to mediate species interactions (Williams and Vickers, 1986; Slattery et al., 2001; Davelos et al., 2004a).
Category: