title: Compensatory density feedback of Oncomelania hupensis populations in two different environmental settings in China.
abstract: BACKGROUND
  The most recent strategy for schistosomiasis control in the People's Republic of China aims to reduce the likelihood of environmental contamination of schistosome eggs. Despite considerable progress, it is believed that achievements would be further consolidated with additional intermediate host snail control measures. We provide an empirical framework for discerning the relative contribution of intrinsic effects (density feedback) from other extrinsic drivers of snail population dynamics.
  
  
  METHODS
  We set up experiments in two study locations to collect reproduction data of Oncomelania hupensis, the intermediate host snail of Schistosoma japonicum. We applied a set of four population dynamic models that have been widely used to study phenomenological time-series data to examine the properties of demographic density feedback patterns from abundance data. We also contrasted the obtained results with the component feedback of density on survival rate to determine whether adult survival was the principal driver of the demographic feedback observed.
  
  
  RESULTS
  Demographic density feedback models (Ricker- and Gompertz-logistic) accounted for > 99% of Akaike's information criterion model weight, with the Gompertz ranking highest in all O. hupensis population groups. We found some evidence for stronger compensatory feedback in the O. hupensis population from Sichuan compared to a Jiangsu population. Survival rates revealed strong component feedback, but the log-linear relationships (i.e. Gompertz) had less support in the demographic feedback analysis.
  
  
  CONCLUSIONS
  Our findings indicate that integrated schistosomiasis control measures must continue to reduce parasite abundance further because intermediate host snail populations tend to grow exponentially at low densities, especially O. hupensis populations in mountainous regions. We conclude that density feedback in adult survival is the principal component contribution to the demographic phenomenon observed in the population fitness (r)-abundance relationship.
authors.affiliation: Jiangsu Institute of Parasitic Diseases, Meiyuan Yangxiang 117, Wuxi 214064, People's Republic of China. guojingyang@hotmail.com
authors.forename: Guo-Jing
authors.initials: GJ
authors.lastname: Yang
authors.forename: Xiao-Nong
authors.initials: XN
authors.lastname: Zhou
authors.forename: Le-Ping
authors.initials: LP
authors.lastname: Sun
authors.forename: Feng
authors.initials: F
authors.lastname: Wu
authors.forename: Bo
authors.initials: B
authors.lastname: Zhong
authors.forename: Dong-Chuan
authors.initials: DC
authors.lastname: Qiu
authors.forename: Jürg
authors.initials: J
authors.lastname: Utzinger
authors.forename: Corey J A
authors.initials: CJ
authors.lastname: Bradshaw
mesh_terms: D000818:Animals; D002681:China; D004199:Disease Vectors; D004783:Environmental Microbiology; D005260:Female; D049851:Gastropoda / Q000254:growth & development*; D008297:Male; D015233:Models, Statistical; D011156:Population Density; D012554:Schistosomiasis japonica / Q000635:transmission