Spatial population dynamics of western painted turtles in a wetland ecosystem in northwestern Montana

Abstract

Population dynamics are driven by the interplay between the positive forces of births and immigration and the negative forces of deaths and emigration. Understanding dynamics at the local and metapopulation level is key in wildlife conservation. Although data on turtle survival and movement rates are available, few studies use rigorous statistical analyses and none include examination of stage-specific seasonal survival simultaneous with movement estimates. I used capture-mark-recapture methods to estimate apparent survival rates and movement probabilities of adult and juvenile western painted turtles (Chrysemys picta bellii) across space and time in a wetland ecosystem in northwestern Montana. All wetlands within five complexes were sampled during three primary sessions a year from fall 2002 to spring 2005. I captured 1,072 individual adults 5,050 times and 442 individual juveniles 3,078 times. Although both juvenile and adult apparent survival rates were influenced by pond, seasons, and year, I found very different patterns spatially and seasonally between age classes. Apparent annual survival was lowest for adults in shallow ponds and lowest for juveniles in deep ponds. This variation could be due to mobility of adults which allows them to seek refugia habitats during drought conditions. Juveniles were less mobile and less likely to leave ponds. Movement probabilities of adults were influenced by distance between ponds and depth of originating pond. Only two juveniles were observed to move between complexes. Although the highest interpopulation movement probability was 3.8%, the probability for most interpopulation movements was very low (\u3c 1%). Temporary emigration estimates were higher than estimates of interpopulation movement indicating the importance of refugia habitat. I examined the potential impacts of road mortality on both the overall population size and population structure via sex and stage class ratios of this population. Road mortality averaged 185 individuals/year. Annual road mortalities ranged widely depending on pond characteristics but in general were higher than the 2-3% mortality suggested by other research to likely affect long-term viability in turtle populations. No highway-induced sex-bias occurred in this population. Population growth rates were negatively influenced by the presence of roads and positively influenced by movements