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Foraging Behaviour of Juvenile Female New Zealand Sea Lions (Phocarctos hookeri) in Contrasting Environments

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      Abstract

      Foragers can show adaptive responses to changes within their environment through morphological and behavioural plasticity. We investigated the plasticity in body size, at sea movements and diving behaviour of juvenile female New Zealand (NZ) sea lions (Phocarctos hookeri) in two contrasting environments. The NZ sea lion is one of the rarest pinnipeds in the world. Most of the species is based at the subantarctic Auckland Islands (AI; considered to be marginal foraging habitat), with a recolonizing population on the Otago Peninsula, NZ mainland (considered to be more optimal habitat). We investigated how juvenile NZ sea lions adjust their foraging behaviour in contrasting environments by deploying satellite-linked platform transmitting terminals (PTTs) and time-depth recorders (TDRs) on 2–3 year-old females at AI (2007–2010) and Otago (2009–2010). Juvenile female NZ sea lions exhibited plasticity in body size and behaviour. Otago juveniles were significantly heavier than AI juveniles. Linear mixed effects models showed that study site had the most important effect on foraging behaviour, while mass and age had little influence. AI juveniles spent more time at sea, foraged over larger areas, and dove deeper and longer than Otago juveniles. It is difficult to attribute a specific cause to the observed contrasts in foraging behaviour because these differences may be driven by disparities in habitat/prey characteristics, conspecific density levels or interseasonal variation. Nevertheless, the smaller size and increased foraging effort of AI juveniles, combined with the lower productivity in this region, support the hypothesis that AI are less optimal habitat than Otago. It is more difficult for juveniles to forage in suboptimal habitats given their restricted foraging ability and lower tolerance for food limitation compared to adults. Thus, effective management measures should consider the impacts of low resource environments, along with changes that can alter food availability such as potential resource competition with fisheries.

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      Early development and fitness in birds and mammals.

      Conditions experienced during early development affect survival and reproductive performance in many bird and mammal species. Factors affecting early development can therefore have an important influence both on the optimization of life histories and on population dynamics. The understanding of these evolutionary and dynamic consequences is just starting to emerge.
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        Food limitation leads to behavioral diversification and dietary specialization in sea otters.

        Dietary diversity often varies inversely with prey resource abundance. This pattern, although typically measured at the population level, is usually assumed to also characterize the behavior of individual animals within the population. However, the pattern might also be produced by changes in the degree of variation among individuals. Here we report on dietary and associated behavioral changes that occurred with the experimental translocation of sea otters from a food-poor to a food-rich environment. Although the diets of all individuals were broadly similar in the food-rich environment, a behaviorally based dietary polymorphism existed in the food-poor environment. Higher dietary diversity under low resource abundance was largely driven by greater variation among individuals. We further show that the dietary polymorphism in the food-poor environment included a broad suite of correlated behavioral variables and that the individuals that comprised specific behavioral clusters benefited from improved foraging efficiency on their individually preferred prey. Our findings add to the growing list of examples of extreme individuality in behavior and prey choice within populations and suggest that this phenomenon can emerge as a behavioral manifestation of increased population density. Individuality in foraging behavior adds complexity to both the fitness consequences of prey selection and food web dynamics, and it may figure prominently as a diversifying process over evolutionary timescales.
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          Robust hierarchical state-space models reveal diel variation in travel rates of migrating leatherback turtles.

          1. Biological and statistical complexity are features common to most ecological data that hinder our ability to extract meaningful patterns using conventional tools. Recent work on implementing modern statistical methods for analysis of such ecological data has focused primarily on population dynamics but other types of data, such as animal movement pathways obtained from satellite telemetry, can also benefit from the application of modern statistical tools. 2. We develop a robust hierarchical state-space approach for analysis of multiple satellite telemetry pathways obtained via the Argos system. State-space models are time-series methods that allow unobserved states and biological parameters to be estimated from data observed with error. We show that the approach can reveal important patterns in complex, noisy data where conventional methods cannot. 3. Using the largest Atlantic satellite telemetry data set for critically endangered leatherback turtles, we show that the diel pattern in travel rates of these turtles changes over different phases of their migratory cycle. While foraging in northern waters the turtles show similar travel rates during day and night, but on their southward migration to tropical waters travel rates are markedly faster during the day. These patterns are generally consistent with diving data, and may be related to changes in foraging behaviour. Interestingly, individuals that migrate southward to breed generally show higher daytime travel rates than individuals that migrate southward in a non-breeding year. 4. Our approach is extremely flexible and can be applied to many ecological analyses that use complex, sequential data.
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            Author and article information

            Affiliations
            [1 ]Department of Zoology, University of Otago, Dunedin, New Zealand
            [2 ]School of Surveying, University of Otago, Dunedin, New Zealand
            [3 ]Department of Conservation, Aquatic & Threats Unit, Wellington, New Zealand
            Texas A&M University-Corpus Christi, United States of America
            Author notes

            Competing Interests: The authors have declared that no competing interests exist.

            Obtained funding and permit: BC. Provided advice on data and statistical analysis: AA AM BR. Conceived and designed the experiments: BC AA. Performed the experiments: BC AA EL. Analyzed the data: EL AA. Contributed reagents/materials/analysis tools: EL AA BC AM BR. Wrote the paper: EL.

            [¤]

            Current address: Australian Research Council Centre of Excellence for Coral Reef Studies, James Cook University, Townsville, Australia

            Contributors
            Role: Editor
            Journal
            PLoS One
            PLoS ONE
            plos
            plosone
            PLoS ONE
            Public Library of Science (San Francisco, USA )
            1932-6203
            2013
            6 May 2013
            : 8
            : 5
            23671630
            3646001
            PONE-D-12-39196
            10.1371/journal.pone.0062728
            (Editor)

            This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

            Counts
            Pages: 10
            Funding
            Data presented in this paper were collected from a long-term study funded by the New Zealand Department of Conservation (DOC) investigation no. 1638, in parallel with fieldwork undertaken for the DOC Conservation Services Program (DOC project Pop 2007/01; http://www.doc.govt.nz/conservation/marine-and-coastal/commercial-fishing/conservation-services-programme/) and through a levy principally on the quota holders of SQU6T. Funding was also provided by the University of Otago Zoology Department. E.L. and A.A. were supported by University of Otago Postgraduate Scholarships. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
            Categories
            Research Article
            Biology
            Ecology
            Behavioral Ecology
            Conservation Science
            Physiological Ecology
            Evolutionary Biology
            Behavioral Ecology
            Marine Biology
            Marine Conservation
            Marine Ecology
            Zoology
            Animal Behavior
            Animal Physiology
            Mammalogy

            Uncategorized

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