|SREL Reprint #1806|
Delayed Sexual Maturity and Demographics of Blanding's Turtles (Emydoidea blandingii): Implications for Conservation and Management of Long-Lived organisms
JUSTIN D. CONGDON
Abstract: A study of Blanding's turtles conducted during 27 of the last 37 years
provided demographic data sufficient to examine how life-history characteristics
may constrain population responses of long-lived organisms. Eight independent
estimates of annual adult survivorship exceeded 93 %. Nest survival was variable
and ranged from 0.0 to 63 % annually, with a mean of 44% from 1976 to 1984
and 3.3 % from 1985 to 1991. Recruitment of juveniles and adults was sufficient
to replace individuals estimated to have died during the study. A life table for the
population resulted in a cohort generation time of 37 years and required a 72%
annual survivorship of juveniles between 1 and 13 years of age to maintain a
stable population. Population stability was most sensitive to changes in adult or
juvenile survival and less sensitive to changes in age at sexual maturity, nest
survival or fecundity. The results from the present study indicate that life-history
traits of long-lived organisms consist of co-evolved traits that result in severe
constraints on the ability of populations to respond to chronic disturbances.
Successful management and conservation programs for long-lived organisms will
be those that recognize that protection of all life stages is necessary. Programs
such as headstarting or protection only of nesting sites, in the absence of
programs to reduce mortality of older juveniles or adults, appear to be less than
adequate to save long-lived organisms such as sea turtles and some tortoises.
The concept of sustainable harvest of already-reduced populations of long-lived
organisms appears to be an oxymoron.
SREL Reprint #1806
Congdon, J.D., A.E. Dunham, and R.C. van Loben Sels. 1993. Delayed sexual maturity and demographics of Blanding's turtles (Emydoidea blandingii): Implications for conservation and management of long-lived organisms. Conservation Biology 7:826-833.