Comparing single-species and mixed-species groups in fruit flies: differences in group dynamics but not group formation

Mixed-species groups describe active associations among individuals of two or more species at the same trophic level. Mixed-species groups are important to key ecological and evolutionary processes such as competition and predation; and ignoring the presence of other species risks ignoring a key aspect of the environment in which social behavior is expressed and selected. Despite the defining emphasis of active formation for mixed-species groups, surprisingly little is known about the mechanisms by which mixed-species groups form. Further, insects have been almost completely ignored in the study of mixed-species groups, despite their taxonomic importance and relative prominence in the study of single-species groups. Here, we measured group formation processes in Drosophila melanogaster and its sister species Drosophila simulans. Each species was studied alone, and together; and one population of D. melanogaster was also studied both alone and with another, phenotypically-distinct D. mel...