Literaturdatenbank
Literaturdatenbank |
|
 |
|
Lovich, J. E. , Life history and demography of turtles of the united states. Unpublished paper presented at USFWS Workshop on Conservation and Trade Management of Freshwater and Terrestrial Turtles in the United States.
Added by: Sarina Wunderlich (06 Jul 2014 16:11:49 UTC) |
| Resource type: Conference Paper BibTeX citation key: anon2010y View all bibliographic details  |
Categories: General Keywords: Habitat - habitat, Nordamerika - North America, Schildkröten - turtles + tortoises, Testudinidae, Testudo graeca, Testudo hermanni Creators: Lovich Collection: USFWS Workshop on Conservation and Trade Management of Freshwater and Terrestrial Turtles in the United States |
Views: 6/470
Views index: 13% Popularity index: 3.25% |
| Abstract |
|
The United States has a diverse turtle fauna with 57 native species, 22 genera and 7 families, or approximately 18% of the world’s turtles. This high diversity is reflected in the fact that the southeastern United States is recognized as a “Turtle Priority Area” for conservation. Recent analysis shows exponential increases in our knowledge of U.S. turtles, as reflected in numbers of published citations. Some species are relatively well-known by this metric while many, including threatened species, are rather poorly-known. Conservation status does not greatly influence status of knowledge although body size and range size do. Almost 40% of U.S. turtle species are threatened, a figure that is not different from the worldwide proportion. Why are turtles such an imperiled group? Research suggests that the driving factors for worldwide reptile declines include 1) habitat loss and degradation, 2) introduced invasive species, 3) environmental pollution, 4) disease, 5) unsustainable use, and 6) global climate change. With respect to unsustainable use, the literature suggests that turtles possess a co-evolved suite of life history traits that constrain their ability to respond to exploitation including 1) low annual fecundity, 2) high nest mortality, 3) delayed maturity, 4) high adult (and post-nest emergence) survivorship, and 5) longevity. The paradigm for turtle population stability suggests that high adult survivorship is necessary to ensure persistence due to the possession of those life history traits, a strategy that has served them well for perhaps more than 200 million years. To assess our knowledge of life history traits in turtles of the United States I gleaned data from the most recent edition of Turtles of the United States and Canada. Second Edition (Ernst and Lovich. 2009. Johns Hopkins University Press. Baltimore. 827 pp). I included data on maximum carapace length; minimum length at maturity for females and males; minimum age of maturity for females; mean hatchling size; mean clutch size; maximum clutch frequency; adult, juvenile and hatchling survivorship; and measures of longevity. Complete data were available for few species (especially survivorship measures) and there was wide variation, often over an order of magnitude, in traits across species. For example, minimum ages at maturity for females ranged from 3 (red-eared slider) to 26 (green seaturtle) years and maximum body size ranges from the diminutive bog turtle (11.5 cm) to the enormous leatherback seaturtle (243.8 cm). For many turtles survivorship must increase rapidly after leaving the nest to compensate for high pre-emergence mortality. Across species life history traits show strong correlations with each other: in larger species females mature at a later age, hatchling size is larger in larger species, mean clutch size and frequency is greater in larger species (although the latter relationship does not account for interannual variation in reproduction), and clutch frequency decreases with adult survivorship. Preliminary analyses suggest weak correlations between female reproductive lifespan (and longevity) and all other traits. Later minimum age of female maturity does not necessarily mean greater longevity and longevity is not necessarily greater in larger species. Cluster analysis identified three groups of correlated traits: one related to longevity; one related to body size; and a third related to maturation, reproductive output, and hatchling survivorship. Principal components analysis identified two factors explaining over 82% of the variation in life history traits. The first axis was related to maximum body size, female maturity size, and clutch size. The second axis was related to adult survivorship and longevity. Complete data were available for 14 species that formed three distinct clusters: one for sea turtles; one with Blanding’s turtle, the desert tortoise and the gopher tortoise; and one for small emydids and other turtles. Published literature based on long-term studies of Blanding’s turtle and the common snapping turtle support the sensitivity of population persistence to adult survival but not to age at maturity, nest survival or fecundity. A small number of turtle species appear to grow rapidly, mature early, and have high fecundity that allow density dependent responses to exploitation but these are in the minority based on available evidence. Exploitation has been documented to affect population size and structure of several turtle species. Due to the long time some species require to reach maturity there is a “perception of persistence” in some turtle populations that can last decades before population decline or extirpation is actually observed. This is in sharp contrast to many traditional game species. As noted by other researchers, turtles have the greatest development of iteroparity and the lowest intrinsic rates of increase of any large order of tetrapods. Indirect effects of turtle commercial exploitation include the spread of disease, the spread of invasive turtle species, genetic pollution, and potential ecological and demographic impacts that are poorly understood. Almost all turtle species that are now extinct, critically endangered or rare were once abundant and overharvest is the main cause. In addition, no species of freshwater turtle or tortoise listed under ESA in the United States has ever been recovered or de-listed. In conclusion, based on a review of the literature, the turtle life history paradigm is supported with very few exceptions: high adult survivorship is necessary to ensure the persistence of turtles with delayed maturity, continued reproductive output, high and variable nest success, and long life spans. Life history evolution of turtles is constrained by a conservative and rigid morphology essentially unchanged since the Triassic. Why would we expect them to change now?
Added by: Sarina Wunderlich |