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DEMOGRAPHY AND VIABILITY ANALYSES OF A DIAMONDBACK TERRAPIN POPULATION
Citation:
Mitro, M. DEMOGRAPHY AND VIABILITY ANALYSES OF A DIAMONDBACK TERRAPIN POPULATION. CANADIAN JOURNAL OF ZOOLOGY 81:716-726, (2003).
Description:
The diamondback terrapin Malaclemys terrapin is a long-lived species with special management requirements, but quantitative analyses to support management are lacking. I analyzed mark-recapture data and constructed an age-classified matrix population model to determine the status and viability of the only known diamondback terrapin population in Rhode Island. Female diamondback terrapins were captured, marked, and recaptured while nesting during 1990-2001. Population growth rate was 1.034 (95% confidence interval = 1.0121.056), indicating a 3.4% average annual increase in the abundance of breeding females. For the past five years, however, abundance was relatively stable at about 188 breeding females. Therefore, population growth occurred primarily in the first half of the study period, and the population might now be considered stable rather than increasing. Adult apparent survival was high but declined slightly by 0.14% per year from 0.959 in 1990 to 0.944 in 2000. Recruitment of breeding females also decreased during the study period; therefore survival was increasingly a greater component of population growth rate. Juvenile survival, derived from the population model, was 0.565 at = 1.034 and 0.446 at = 1. Both retrospective (mark-recapture) and prospective (matrix population model) analyses showed a greater influence of survival versus reproduction on population growth. Population model projections showed that capping nests to improve reproductive success could increase population growth, but the magnitude of increase was positively related to pre-reproductive survival, therefore negating nest capping as a remedy for declining populations or poor survival. I also discuss the viability of the population in relation to demographic, environmental, and catastrophic stochasticity and show that extinction attributable to demographic stochasticity is unlikely.