Differences in reward removal efficiency and its consequences for seed germination in the ant-dispersed sedge Carex tristachya (Cyperaceae) Koki Tanaka . Sumire Haramoto . Makoto Tokuda Received: 3 July 2018 / Accepted: 26 September 2018 Ó Springer Nature B.V. 2018 Abstract Reward removal is an essential step for seed dispersal mutualism because residual rewards inhibit germination. Nevertheless, variation in the reward removal efficiency (RRE) among dispersers and its consequences for germination have rarely been reported. In this study, we compared the RREs of two sympatric seed-dispersing ants, Formica japonica and Pheidole noda, using seeds of the ant-dispersed sedge Carex tristachya. Then, we conducted seed sowing experiments in a non-heated glasshouse to evaluate the effect of RRE on the percentage and speed of germination. The majority (85%) of seeds handled by F. japonica had residual elaiosomes, while elaio- somes were completely removed from all seeds handled by P. noda, demonstrating that P. noda has much higher RRE than F. japonica. The seed sowing experiments revealed that RRE, defined by the pres- ence or absence of residual elaiosomes, was not associated with the percentage germination within a year. However, high RRE seeds with no residual elaiosomes germinated significantly faster than low RRE seeds with residual elaiosomes. Similarly, arti- ficial removal of elaiosomes from C. tristachya seeds accelerated germination speed without affecting germination percentage. These results suggest that RRE is one of the most important parameters deter- mining the effectiveness of a seed dispersal agent. Keywords Myrmecochory Á Elaiosome Á Germination Á Seed dispersal effectiveness Introduction Seed dispersal mutualism is an important animal– plant interaction for the regeneration of many plants across the world (Howe and Smallwood 1982) because it both assists seed movement into favorable sites (Augspurger 1984; Hanzawa et al. 1988; Wenny and Levey 1998; Fragoso et al. 2003) and improves seed germination (Traveset and Verdu ´ 2002; Garrido et al. 2009; Fedriani et al. 2012; Fricke et al. 2013). Nevertheless, seed dispersal effectiveness can vary significantly depending on the attributes of the seed dispersers (Giladi 2006; Schupp et al. 2010). This can result in regeneration failure in some regions where native seed dispersers have been replaced by exotic species whose dispersal effectiveness is low (Christian 2001; Rodriguez-Cabal et al. 2012). Moreover, vari- ations in effectiveness among dispersers have often been assumed to be the main selective pressure for the evolution of trait specialization in animal-dispersed plants (Thies and Kalko 2004; Tanaka and Tokuda 2016, 2017). Therefore, identifying the attributes that Communicated by E.T.F Witkowski. K. Tanaka (&) Á S. Haramoto Á M. Tokuda Faculty of Agriculture, Saga University, Saga 840-8502, Japan e-mail: koukin817@gmail.com 123 Plant Ecol https://doi.org/10.1007/s11258-018-0886-3