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:Anemone saturation is a measure of the density of fish in each anemone (Buston 2003a), and local density might influence the fitness of breeders (Tupper and Boutilier 1995; Hixon and Carr 1997).
Category: