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:Ecological risks of Japanese knotweed include outcompeting native plants, directly for light and water and indirectly via alleopathy (Dommanget et al. 2014), and changing habitat structure for animals (Engler et al. 2011).
Category: