The population ecology of a natural population of the pierid butterfly Colias alexandra

Summary Key factor analysis techniques were used to examine factors determining the abundance of a population of non-pest Colias. The number of individuals entering each successive life stage in the sample population are summarized in life tables for 1975 to 1979. Survivorship to the adult is a relatively consistent proportionality (-x=1.2%, S.D.=1.14; 1975–1979). Factors resulting in reduced natality and, less importantly, mortality during larval diapause determine the population trends for C. alexandra. Egg mortality, pre-diapause larval mortality and postdiapause mortality contribute little to these trends. Possible key sources contributing to reduced natality are examined. Mortality of adults (including removal by collectors), poor weather conditions during the oviposition period, unseasonal snow or drought which affect nectar sources or oviposition sites are among the factors which cause reduced natality and result in population depression.