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      Seasonal and life-stage variation in the reproductive ecology of a marine apex predator, the tiger shark Galeocerdo cuvier, at a protected female-dominated site

      , , , , ,
      Aquatic Biology
      Inter-Research Science Center

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          Coefficients of Determination in Logistic Regression Models—A New Proposal: The Coefficient of Discrimination

          Tue Tjur (2009)
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            State-dependent risk-taking by green sea turtles mediates top-down effects of tiger shark intimidation in a marine ecosystem.

            1. A predictive framework of community and ecosystem dynamics that applies across systems has remained elusive, in part because non-consumptive predator effects are often ignored. Further, it is unclear how much individual-level detail community models must include. 2. Previous studies of short-lived species suggest that state-dependent decisions add little to our understanding of community dynamics. Body condition-dependent decisions made by long-lived herbivores under risk of predation, however, might have greater community-level effects. This possibility remains largely unexplored, especially in marine environments. 3. In the relatively pristine seagrass community of Shark Bay, Australia, we found that herbivorous green sea turtles (Chelonia mydas Linnaeus, 1758) threatened by tiger sharks (Galeocerdo cuvier Peron and LeSueur, 1822) select microhabitats in a condition-dependent manner. Turtles in poor body condition selected profitable, high-risk microhabitats, while turtles in good body condition, which are more abundant, selected safer, less profitable microhabitats. When predation risk was low, however, turtles in good condition moved into more profitable microhabitats. 4. Condition-dependent use of space by turtles shows that tiger sharks modify the spatio-temporal pattern of turtle grazing and their impacts on ecosystem dynamics (a trait-mediated indirect interaction). Therefore, state-dependent decisions by individuals can have important implications for community dynamics in some situations. 5. Our study suggests that declines in large-bodied sharks may affect ecosystems more substantially than assumed when non-lethal effects of these top predators on mesoconsumers are not considered explicitly.
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              Satellite tagging and cardiac physiology reveal niche expansion in salmon sharks.

              Shark populations are declining globally, yet the movements and habitats of most species are unknown. We used a satellite tag attached to the dorsal fin to track salmon sharks (Lamna ditropis) for up to 3.2 years. Here we show that salmon sharks have a subarctic-to-subtropical niche, ranging from 2 degrees to 24 degrees C, and they spend winter periods in waters as cold as 2 degrees to 8 degrees C. Functional assays and protein gels reveal that the expression of excitation-contraction coupling proteins is enhanced in salmon shark hearts, which may underlie the shark's ability to maintain heart function at cold temperatures and their niche expansion into subarctic seas.
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                Author and article information

                Journal
                Aquatic Biology
                Aquat. Biol.
                Inter-Research Science Center
                1864-7782
                1864-7790
                February 22 2016
                February 22 2016
                : 24
                : 3
                : 175-184
                Article
                10.3354/ab00648
                036a3a31-33c4-44d6-a04a-e81ce710add5
                © 2016
                Product
                Self URI (article page): http://www.int-res.com/abstracts/ab/v24/n3/p175-184/

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