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:H. axyridis was recorded in the Ryukyu Islands
(Poutsma et al. 2008; GBIF 2013), but Noriyuki et al.
(2012) report that it does not occur there.
Category: