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:Although South American Pleistocene climate changes have been demonstrated not to be the only driver of speciation (e.g. Hoorn et al. 2010; Rull 2011), they have influenced the historical demography and distribution of some species in South America.
Category: