1. School of Mathematics, Hangzhou Normal University, Hangzhou, 311121, China, and School of Mathematics and Statistics, Central South University, Changsha 410083, China.
2. School of Mathematics, Hangzhou Normal University, Hangzhou, 311121, China.
3. Corresponding author. Department of Mathematical and Statistical Sciences & Interdisciplinary Lab for Mathematical Ecology and Epidemiology, University of Alberta, Edmonton, AB T6G 2G1, Canada.