24 research outputs found

    Importance of Marine-Derived Nutrients Supplied by Planktivorous Seabirds to High Arctic Tundra Plant Communities

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    <div><p>We studied the relative importance of several environmental factors for tundra plant communities in five locations across Svalbard (High Arctic) that differed in geographical location, oceanographic and climatic influence, and soil characteristics. The amount of marine-derived nitrogen in the soil supplied by seabirds was locally the most important of the studied environmental factors influencing the tundra plant community. We found a strong positive correlation between <i>δ</i><sup>15</sup>N isotopic values and total N content in the soil, confirming the fundamental role of marine-derived matter to the generally nutrient-poor Arctic tundra ecosystem. We also recorded a strong correlation between the <i>δ</i><sup>15</sup>N values of soil and of the tissues of vascular plants and mosses, but not of lichens. The relationship between soil <i>δ</i><sup>15</sup>N values and vascular plant cover was linear. In the case of mosses, the percentage ground cover reached maximum around a soil <i>δ</i> <sup>15</sup>N value of 8‰, as did plant community diversity. This soil <i>δ</i><sup>15</sup>N value clearly separated the occurrence of plants with low nitrogen tolerance (e.g. <i>Salix polaris</i>) from those predominating on high N content soils (e.g. <i>Cerastium arcticum</i>, <i>Poa alpina</i>). Large colonies of planktivorous little auks have a great influence on Arctic tundra vegetation, either through enhancing plant abundance or in shaping plant community composition at a local scale.</p></div

    RDA ordination diagram based on N and C contents (%) and isotopic signatures (<i>δ</i><sup>15</sup>N and <i>δ</i><sup>13</sup>C, ‰) of vascular plants, mosses and lichens (response variables) in relation to the same parameters in soil (explanatory variables).

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    <p>RDA ordination diagram based on N and C contents (%) and isotopic signatures (<i>δ</i><sup>15</sup>N and <i>δ</i><sup>13</sup>C, ‰) of vascular plants, mosses and lichens (response variables) in relation to the same parameters in soil (explanatory variables).</p

    Beluga whale summer habitat associations in the Nelson River estuary, western Hudson Bay, Canada

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    <div><p>To understand beluga whale (<i>Delphinapterus leucas</i>) estuarine use in the Nelson River estuary, southwest Hudson Bay, we recorded and examined beluga movements and habitat associations for the July through August period in 2002–2005. We compared locations of belugas fitted with satellite transmitters (“tags”) (2002–2005) and aerial-surveyed (2003 and 2005) belugas for years of differing freshwater flow from the Nelson River which is influenced by hydroelectric activity. Using the beluga telemetry location data, we estimated an early August behavioral shift in beluga distribution patterns from local estuarine use to a progressively more migratory behavior away from the estuary. The timing of this shift in behavior was also apparent in results of beluga aerial surveys from the 1940s–1960s, despite environmental changes including later freeze-up and warming ocean temperatures. Overall, during the higher than average discharge (“wet”) year of 2005, the three tagged belugas ranged farther from the Nelson River but not farther from the nearest shore along southwestern Hudson Bay, compared to the 10 tagged belugas tracked during the “dry” years of 2002–2004 with below average discharges. Aerial survey data for 2003 and 2005 display a similar dry vs. wet year shift in spatial patterns, with no significant change in overall density of belugas within the study area. In the Nelson estuary, proximity to the fresh-salt water mixing area may be more important than the shallow waters of the upper estuary. Killer whales (<i>Orcinus orca</i>) were observed in the Churchill area (200 km northwest) during each year of study, 2002–05, and belugas may benefit from the proximity to shallow estuary waters that provide protection from the larger-bodied predator. Study results contribute to an understanding of the influence of environmental variation on how and why belugas use estuaries although considerable uncertainties exist and additional research is required.</p></div

    Mean δ<sup>13</sup>C and δ<sup>15</sup>N values (solid lines) and confidence intervals (dotted lines) of fur seal whiskers.

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    <p>Isotopic values were averaged by species (<i>A. gazella</i> (black) and <i>A. tropicalis</i> (grey)) and sex (males (left panels) and females (right panels)) over a time period of 4 consecutive years. Time zero that corresponds to the newly synthesized part of the whiskers appears on the right of plots.</p

    Whisker δ<sup>13</sup>C and δ<sup>15</sup>N values of individual fur seals.

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    <p>Values are means ± the mean amplitude of the cyclic patterns. Note that bars do not represent standard or error bars, but the entire isotopic range of seals. Dashed gray lines illustrate the isotopic estimation of fronts (see text). APF: Antarctic Polar Front; STF: Subtropical Front.</p

    Overall length, δ<sup>13</sup>C and δ<sup>15</sup>N values and C∶N mass ratio of fur seal whiskers from Crozet Islands.

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    <p>Values are means ± SD, with ranges in parentheses.</p>a<p>Fourteen samples were deleted because they corresponded to the suckling period of two females when they were pups, thus increasing the δ<sup>15</sup>N range (see text and <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0032916#pone-0032916-g004" target="_blank">Fig. 4</a>).</p

    General study area (inset), including the Nelson River estuary in southwest Hudson Bay displaying the telemetry-derived estuary area (dashed line), the aerial survey transects, the site of beluga capture, and the freshwater plume (in blue) derived from a MODIS Aqua image from 8 August, 2000.

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    <p>General study area (inset), including the Nelson River estuary in southwest Hudson Bay displaying the telemetry-derived estuary area (dashed line), the aerial survey transects, the site of beluga capture, and the freshwater plume (in blue) derived from a MODIS Aqua image from 8 August, 2000.</p
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