Behaviour 151 (2014) 769–780 brill.com/beh Association tendency and preference for heterospecifics in an invasive species M. Camacho-Cervantes a,∗ , A.F. Ojanguren a , A.E. Deacon a , I.W. Ramnarine b and A.E. Magurran a a Centre for Biological Diversity, University of St. Andrews, St. Andrews, Fife, UK b Department of Life Sciences, The University of the West Indies, St. Augustine, Trinidad and Tobago * Corresponding author’s e-mail address: mcc4@st-andrews.ac.uk Accepted 9 December 2013; published online 17 January 2014 Abstract Animals gain benefits by forming groups with phenotypically and behaviourally similar individu- als. The most common groups are homogenous, composed by conspecifics, although in some cases associations of similar organisms of different species have been reported when individuals benefit from it. In this study, we tested the prediction that the Trinidadian guppy, Poecilia reticulata, a fish that has successfully invaded at least 70 countries, will shoal with heterospecifics. We measured shoaling tendency and shoal companion preference in wild-caught female guppies when they en- counter two heterospecific species: the native Poecilia picta and the non-native Poecilia sphenops, a poeciliid recently introduced in Trinidad. Our results show that guppies have a higher tendency to shoal with conspecifics; if the alternative is be alone, they readily shoal with both species even when they have had no previous experience with other poeciliids. Individuals in these associations could benefit from safety in numbers along with other advantages of group living. This predis- position to associate with other species that share similar ecological conditions could explain the guppy’s success as invasive species as it enables them to increase their shoal size during the first stages of invasion and thus avoid Allee effects. Keywords invasion success, social behaviour, fish, Trinidad, shoaling tendency, shoaling prefer- ence, benefits. 1. Introduction Many animals form groups to gain benefits at the individual level. Benefits for each individual joining a group include a reduction in predation risk  2014 Koninklijke Brill NV, Leiden DOI:10.1163/1568539X-00003169