This study investigated the relationship between the processes and microbial populations induced by long-term starvation. To demonstrate the effects of starvation, a laboratory-scale anaerobic reactor was operated in three phases (first reaction, starvation, second reaction) for 316 days. During the first reaction, the chemical oxygen demand (COD) concentration decreased by about 70% of the input swine wastewater and 64 L of methane gas was produced: during the second reaction, there was a 63% COD reduction and 36 L of methane was produced. The methanogenic diversity, qualitatively monitored with denaturing gradient gel electrophoresis using archaeal 16S rRNA gene primers, was not different between two reactions. However, DNA copy numbers of Methanosarcinales, quantitatively monitored with quantitative real-time polymerase chain reaction using order-level 16S rRNA gene primers, showed the changed results. Cell numbers of Methanosarcinales and methanogenic activity were important factors determining the different efficiencies of the process. (C) 2009 Elsevier Ltd. All rights reserved.