The Evolutionary and Mathematical Demography of the Turtle Chrysemys picta
1975
Wilbur, Henry M.
A mark—recapture study of a population of painted turtles, Chrysemys picta, started by O. J. Sexton between 1953 and 1957 was continued between 1968 and 1973. Life tables are constructed and a demographic history of the population is suggested. Males mature during their 4th yr and first breed at age five. Females mature at age seven and lay two clutches of about 6 to 7 eggs each year. Mortality is about 92% between laying and the arrival of the hatchlings at the pond. Juvenile and adult mortality is at a constant exponential rate of about 0.15 for males and 0.18 for females each year. Raccoons, Procyon lotor, are an important predator during spring migrations. There is no indication of senescence; females over 30 yr old are still reproductive. Between 1954 and 1972 the population's size has been reduced from an estimated 981 to about 186 animals. This has been accompanied by a decrease in mean generation time from 12.35 to 10.70 yr. Survivorship from laying to arrival at the pond has more than doubled, but adult survivorship has decreased. These changes are attributed to an increased predation rate resulting from a reduction in the number of safe basking sites. A hypothetical population was simulated by recurrent use of a population projection matrix, derived from the 1954 life table, to demonstrate the stability characteristics of this long—lived, iteroparous species. The evolution of this life history is interpreted as an adaptation to a highly uncertain probability of nest success and an effective predator defense in the adult stage.
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