| For better management of biodiversity， it is imperative to understand process that allows sympatric occurrence of related species. Sympatric species can differ in various life-history traits which have presumably been selected under surrounding environmental constraints. We examined the preference and availability of food resource for two sympatric species of unionoid mussels， U. douglasiae and L. grayana， in relation to their mobility and growth characteristics(i.e.， growth rates and longevity). Field survey was conducted in floodplain water bodies(FWB) of Kiso River， Japan. Mobility was determined by mark-recaptures of individuals. Growth characteristics were determined by repeated measures of bagged individuals. Begged individuals were eventually sacrificed and measured for C/N stable isotope ratio together with potential food resoueces. Unio douglasiae grew faster， and was shorter-lived and more mobile， compared with L. grayana; the former selectively fed on seston(largely phytoplankton) whereas the latter showed broader food selection. Primary productivity gradient explained the FWB-scale habitat distribution of two species. Observed life-history traits matched benefical surviving strategies in respective habitat， suggesting the role of specialization of trophic position for their sympatric occurrence. |
