Population Growth
Population Growth:
Because the Blanding's Turtles hibernate throughout late fall, winter, and early spring months, they are difficult to locate and complete population counts for. In addition, the female turtles are always relocating for nesting season and then returning to the wetlands after laying their eggs. Therefore, there is only a population estimate of about 10,000 individuals for the Great Lakes and St. Lawrence population (8). The population size for the Quebec population and Nova Scotia population is estimated to be very small. There is no historical data regarding the population of this species in previous years.
Because the Blanding's Turtles hibernate throughout late fall, winter, and early spring months, they are difficult to locate and complete population counts for. In addition, the female turtles are always relocating for nesting season and then returning to the wetlands after laying their eggs. Therefore, there is only a population estimate of about 10,000 individuals for the Great Lakes and St. Lawrence population (8). The population size for the Quebec population and Nova Scotia population is estimated to be very small. There is no historical data regarding the population of this species in previous years.
Life History:
Blanding's Turtles are sexually mature between the ages of fourteen and twenty years (6). Blanding's Turtles are capable of reproducing every year (6). Blanding's Turtles can have up to twenty offspring at one time, but generally this number is around ten (6). Blanding's Turtles is a very long-lived species. It is capable of surviving in excess of seventy years (6). |
Measuring Population Growth: Fecundity and Survivorship
Fecundity:
Since 1930, many studies have been conducted by the University of Michigan, who gained access to the Edwin S. George Reserve, a large 1300-acre fenced preserve that was used to promote research and education (2).
A female Blanding's Turtle becomes sexually mature between the age of fourteen and twenty years (6). On average, a female Blanding's Turtle is capable of producing one clutch every year; however, some Blanding's Turtles produce one clutch every two to three years. Each clutch consists of two to twenty eggs, with the average number of eggs in one clutch being ten (6). The size of the clutch produced depends greatly on the size of the female turtle, increasing with the turtle's body size.
The temperature at which the eggs are incubated at determines the sex of the turtle. Eggs incubated under twenty-eight degrees Celsius will be males, and eggs incubated over twenty-nine degrees Celsius will be females (8). The average annual fecundity, or the number of female eggs produced per female turtle, is about four (9).
Predation rates of Blanding's Turtle hatchlings were studied over twenty-three years in the ESGR in Michigan. It was concluded that a mean of seventy-eight percent of the nests had been predated, with predation rates ranging from forty percent to one hundred percent (6). Among the nests that survived predation, twenty percent failed entirely, and forty-five percent had at least one egg fail.
Since 1930, many studies have been conducted by the University of Michigan, who gained access to the Edwin S. George Reserve, a large 1300-acre fenced preserve that was used to promote research and education (2).
A female Blanding's Turtle becomes sexually mature between the age of fourteen and twenty years (6). On average, a female Blanding's Turtle is capable of producing one clutch every year; however, some Blanding's Turtles produce one clutch every two to three years. Each clutch consists of two to twenty eggs, with the average number of eggs in one clutch being ten (6). The size of the clutch produced depends greatly on the size of the female turtle, increasing with the turtle's body size.
The temperature at which the eggs are incubated at determines the sex of the turtle. Eggs incubated under twenty-eight degrees Celsius will be males, and eggs incubated over twenty-nine degrees Celsius will be females (8). The average annual fecundity, or the number of female eggs produced per female turtle, is about four (9).
Predation rates of Blanding's Turtle hatchlings were studied over twenty-three years in the ESGR in Michigan. It was concluded that a mean of seventy-eight percent of the nests had been predated, with predation rates ranging from forty percent to one hundred percent (6). Among the nests that survived predation, twenty percent failed entirely, and forty-five percent had at least one egg fail.
Survivorship: The adult survivorship for Blanding's Turtles is high, and some individuals can reach ages over seventy years in the wild (6). The average survival rate of a Blanding's Turtle egg and its hatchling is about 0.026. The average survival rate of this species aged one to six years, a juvenile, is 0.159. The average survival rate of these turtles aged seven to thirteen, a subadult, is 0.185. The average survival rate for adult Blanding's Turtles is about 0.629 (9). |
Predation:
There are many animals that prey on the Blanding's Turtle. This is a limiting factor to the population size and growth because it decreases the number of turtles in the population. Turtles' eggs are an easy target for animals such as coyotes, foxes, raccoons, and skunks (4). When animals feast on turtle's eggs, these hatchlings cannot become part of the population and survive to reproductive age. This eliminates the chance of the species population size increasing. |
http://www.conserveturtles.org/seaturtleinformation.php?page=threats
http://www.robertmccaw.com/galleries/get_samples.php?gallery=miscellaneous:predation-predator-prey:predation-predator-prey |