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Investigating Potential for Depensation in Marine Turtles: How Low Can You Go?

Authors

  • C. D. BELL,

    1. Marine Turtle Research Group, Centre for Ecology and Conservation, University of Exeter, Cornwall Campus, Penryn TR10 9E2, United Kingdom
    2. Pendoley Environmental, P.O. Box 98, Leederville, WA 6902, Australia
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  • J. M. BLUMENTHAL,

    1. Marine Turtle Research Group, Centre for Ecology and Conservation, University of Exeter, Cornwall Campus, Penryn TR10 9E2, United Kingdom
    2. Department of Environment, P.O. Box 486, George Town, Grand Cayman, Cayman Islands
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  • A. C. BRODERICK,

    1. Marine Turtle Research Group, Centre for Ecology and Conservation, University of Exeter, Cornwall Campus, Penryn TR10 9E2, United Kingdom
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  • B. J. GODLEY

    Corresponding author
    1. Marine Turtle Research Group, Centre for Ecology and Conservation, University of Exeter, Cornwall Campus, Penryn TR10 9E2, United Kingdom
      email b.j.godley@exeter.ac.uk
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email b.j.godley@exeter.ac.uk

Abstract

Abstract: Where mechanisms inherent within the biology of a species affect individual fitness at low density, demographic-scale depensation may occur, hastening further decline and leading ultimately to population extirpation and species extinction. Reduction in fertility at low population densities has been identified in marine and terrestrial species. Using data on hatch success and hatchling-emergence success as proxies for fertilization success, we conducted a global meta-analysis of data from breeding aggregations of green turtles (Chelonia mydas) and loggerhead turtles (Caretta caretta). We found that there has been no reduction in fertility in small nesting aggregations in either of these species worldwide. We considered mechanisms within the mating strategies and reproductive biology of marine turtles that may allow for novel genetic input and facilitate enhanced gene flow among rookeries. Behavioral reproductive mechanisms, such as natal philopatry and polyandry, may mitigate potential impacts of depensation and contribute to the resilience of these species.

Abstract

Resumen: Cuando los mecanismos inherentes a la biología de una especie afectan la eficacia individual a baja densidad, puede ocurrir la anticompensación, que acelera la declinación y en última instancia conduce a la extirpación de la población y a la extinción de la especie. La reducción de fertilidad en poblaciones con baja densidad se ha identificado en especies marinas y terrestres. Utilizando datos de éxito de eclosión y emergencia de crías como indicadores del éxito de fertilización, realizamos un meta-análisis global de datos de agregaciones de tortugas verdes (Chelonia mydas) y tortugas caguama (Caretta caretta). Encontramos que no ha habido reducción en la fertilidad en agregaciones pequeñas de estas dos especies. Consideramos los mecanismos en las estrategias de apareamiento y de la biología reproductiva de tortugas marinas que pueden permitir el ingreso de material genético nuevo y facilitar el flujo de genes entre colonias. Mecanismos de la conducta reproductiva, como la filopatría natal y la poliandria, pueden mitigar impactos potenciales de la anticompensación y contribuir a la resiliencia de estas especies.

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