A new paradigm for the conservation of turtles [electronic resource] : ecosystem-based approaches for understanding population variability

Reptiles and amphibians are the world's most threatened vertebrate taxa. Turtles have experienced global population declines and 62% of species are currently in danger of extinction. Like all herpetofauna, the main threat to turtles is habitat loss, fragmentation, and degredation. Even in protected areas, turtle populations can enigmatically decline. This, in combination with the fragility of populations on a global level, has resulted in widespread use of manipulative captive rearing conservation technologies. Recent research demonstrates that manipulative technologies are ineffective and instead suggests the adoption of an ecosystem-based research approach from which a new paradigm for turtle conservation may be generated. This thesis directly undertakes this challenge, examining turtle populations across a variety of ecosystems through behavioral, demographic, life history, health, and life cycle lenses. The western pond turtle, the only native freshwater turtle on the western coast of the United States, is used as a model system and is studied in five distinct sites in Central California. Whereas previous literature only documented aggression, this study revealed a complex repertoire of basking behaviors and interactions. Demographic models generated population estimates between 3 and 322 individuals, illustrating profound population size differences across habitats and ecosystems. Temperature regimes explained variation in western pond turtle size, survival, and growth, whereas the level of urbanization explained variation in demographic characteristics, such as population size, sex ratio, and life stage distribution. Combined characteristics of oak woodlands and oak savanna ecosystems subjected to anthropogenic impact resulted in an acceleration of the normally `slow' turtle life history. Thermal regimes were also associated with health conditions of western pond turtles, such as aural abscesses, which are reported for the first time in this study. The etiologies of conditions such as aural abscesses, shell deformities, hyperphosphatemia, hypocalcemia, and hypoproteinemia, appear to be related to the interaction of temperature regimes, water quality, and nutrition. High numbers of physical anomalies and aural abscesses in juveniles suggest risk factors are higher for juveniles than adults, and that the origin of adult hyperphosphatemia, hypocalcemia, and hypoproteinemia is the juvenile developmental period. The application of an unsupervised artificial neural network to our data revealed four main inhibitors to western pond turtle life cycle completion: 1) levels of female predation during nesting migration high enough to skew the population sex ratio to a male-dominated sex ratio, 2) lack of or insufficiency of nesting habitat resulting in high enough female mortality or low enough breeding female recruitment (or a combination thereof) to maintain male-biased population sex ratios, 3) general lack or insufficiency of nesting habitat, and 4) lack or insufficiency of overwintering habitat associated with turtle sickness. These results demonstrate the importance of high quality terrestrial habitat for the long-term persistence of western pond turtle populations. Our results show that variation in biotic and abiotic conditions can shift the western pond turtle life history along the slow-fast continuum and influence demographic rates, with physiological consequences for the individual animal. This ecosystem-based study of turtle populations has cast a novel spotlight on a previously under-recognized component of the freshwater turtle life cycle and life history, the influence of the environment on juvenile development. Life history parameters for juveniles and the proportion of juveniles in populations varied with environmental characteristics. The health of adults provided a window for viewing the conditions experienced during development and illustrated the consequences of juvenile growth in habitats with limited options for required thermoregulation. While turtle conservation is still largely operating under a manipulative paradigm that emphasizes juvenile survivorship, the result of this ecosystem-based study of turtle biology is a paradigm that shifts the focus instead to the quality of juvenile development and its subtle but intricate thermal dependence, governed by the structure and condition of the habitat and ecosystem.

Keywords: Biology.
Advisor: Dirzo Rodolfo primary advisor. Thesis advisor
De Leo Giulio A. advisor. Thesis advisor
Denny Mark W.
Fukami Tadashi