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:(2010) demonstrated that the development of external sexual change of krill is accelerated by photoperiod, although others have shown that the cyclic maturation process is maintained independent of direct control by environmental factors such as food or light (Thomas and Ikeda 1987; Kawaguchi et al. 2007).
Category: