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3 Conceptual Model of Sea-Turtle Abundance and Demography
Pages 43-54

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From page 43...
... Thus, the number of adult females in a population in a year consists of the ones that nest in that year and the ones that remain at sea. The latter number, which typically is not measured, depends on the numbers nest­ ing in previous years, their remigration intervals (the interval between successive nesting seasons)
From page 44...
... Taken together, those complications in the use of nest counts as an index of population abun­ dance underscore the importance of demographic and other information in drawing robust conclusions about a sea­turtle population from obser­ vations limited to one part of the population at one stage of the lifecycle. Hence, a conceptual model that links population abundance with the key demographic processes in a single coherent framework is needed.
From page 45...
... FIGURE 3.1 A conceptual or causal­loop diagram summarizing the ageclass structure and key demographic processes of the model accounting for the population dynamics of Pacific loggerhead sea­turtle populations exposed to various ageclass­specific anthro­ pogenic hazards. +/­ = causal­loop polarity: + means two components move in same direction, and ­ means they move in opposite directions.
From page 46...
... . A Bayesian belief network modeling approach based on the conceptual model shown in Figure 3.1 has been proposed for assessment of the relative risk posed by exposure for sea­turtle populations in Southeast Asian waters to multiple anthropogenic hazards (Chaloupka, 2007)
From page 47...
... Neritic immatures and adults are assumed to be subject to compensa­ tory density­dependent functions; as the population density increases, the neritic component of the population is regulated by per capita food supply. Major Demographic Processes The major demographic processes included in the conceptual model are (1)
From page 48...
... breeding each year in two loggerhead populations that make up the southwestern Pacific genetic stock (data from Limpus et al., 1994; Limpus and Limpus, 2003a; courtesy of M Chaloupka)
From page 49...
... Assuming successful mating, the female loggerheads then lay a variable number of clutches of eggs on the sandy beaches at the rookeries over the summer nesting season. Temperature-Dependent Hatching and Sex Determination The probability of eggs hatching (Figure 3.2c)
From page 50...
... growth functions have been developed by Chaloupka (2003a) for southwestern Pacific neritic female loggerheads (see Figure 3.2g)
From page 51...
... used satellite telemetry to derive estimates of oceanic juvenile annual survival probabilities of 64–81%. No such oceanic ageclass annual­survival probability estimates exist for Pacific loggerhead populations.
From page 52...
... The major anthropogenic hazards to loggerhead sea turtles in general included in the conceptual demographic model are as follows (Bolten et al., 2010) : • Climate change that affects sea level and leads to beach washover and inundation of nests (Daniels et al., 2006)
From page 53...
... . Those hazards have a direct effect on the long­term viability of a loggerhead sea­ turtle population on the basis of the following key demographic metrics (Chaloupka and Limpus, 2001; Matsuzawa et al., 2002; Bjorndal et al., 2003b; Chaloupka, 2003a; Heppell et al., 2003; Limpus and Limpus, 2003a; Mazaris et al., 2005, 2006)


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