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首页> 外文期刊>Marine biology >Habitat use and group size of pied cormorants (Phalacrocorax varius) in a seagrass ecosystem: possible effects of food abundance and predation risk
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Habitat use and group size of pied cormorants (Phalacrocorax varius) in a seagrass ecosystem: possible effects of food abundance and predation risk

机译：海草生态系统中斑cor（斑ala）的栖息地使用和种群大小：食物丰富和捕食风险的可能影响

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Both food abundance and predation risk may influence habitat use decisions. However, studies of habitat use by birds in marine environments have focused only on food abundance. I investigated the possible influences of food abundance and predation risk from tiger sharks (Galeocerdo cuvier) on habitat use by pied cormorants (Phalacrocorax varius) over two spatial scales and on cormorant group size. Cormorants were usually solitary, but group size was highest in shallow habitats during months when shark density was low. Regardless of season, cormorant density within shallow habitats was higher over seagrass than sand, and cormorants were distributed between these two microhabitats proportional to prey density. Therefore, cormorants appear to respond to prey abundance at a relatively narrow spatial scale (i.e., tens of meters). At the habitat-patch scale (∼ 1 km), the density of cormorants and their prey (teleosts) was higher in shallow habitats than in deep ones, but the density of cormorants was influenced by an interaction between water temperature (i.e., season) and habitat. There was decreased use of shallow habitats as water temperature, and the density of tiger sharks, increased. When shark density was low, cormorants were distributed across habitats roughly in proportion to the abundance of fish, suggesting that cormorants respond to food abundance at the scale of habitat patches. However, as shark abundance increased, the relative density of cormorants dropped in the dangerous shallow habitats such that there was a greater density of cormorants relative to their food in deep habitats when sharks were abundant. This suggests that pied cormorants trade-off food and risk by accepting lower energetic returns to forage in safer habitats. This study provides the first evidence that marine habitat selection by birds may be influenced by such a trade-off, and provides further evidence that tiger sharks are important in determining habitat use of their prey and mediating indirect interactions within Shark Bay.
机译：食物丰富和捕食风险都可能影响栖息地使用的决策。但是，对海洋环境中鸟类栖息地利用的研究仅集中在食物丰度上。我调查了虎鲨（Galeocerdo cuvier）的食物丰富度和捕食风险对斑d（Phalacrocorax varius）在两个空间尺度上的栖息地使用以及cor群大小的可能影响。 usually通常是单生的，但在鲨鱼密度低的月份中，浅水区的group最大。无论季节如何，海草上浅层生境中的cor密度都比沙子高，并且ants在这两个微生境之间的分布与猎物密度成比例。因此，cor似乎在相对狭窄的空间范围内（即几十米）对猎物的数量做出反应。在栖息地斑块规模（＆SIM; 1 km）上，浅栖息地的cor及其猎物（远洋te）的密度高于深栖息地，但cor的密度受水温（即季节）之间相互作用的影响）和栖息地。随着水温的升高，浅层生境的使用减少，虎鲨的密度增加。当鲨鱼密度低时，cor在整个生境中的分布与鱼类的丰富程度大致成比例，这表明cor对生境斑块范围内的食物丰富做出了响应。但是，随着鲨鱼数量的增加，the在危险的浅层生境中的相对密度会下降，因此，在鲨鱼丰富的情况下，深deep生境中food的密度相对于其食物会更大。这表明花pie在较安全的生境中接受较低的能量回馈来觅食，从而权衡了食物和风险。这项研究提供了第一个证据，表明鸟类对海洋栖息地的选择可能会受到这种折衷的影响，并提供进一步的证据，表明虎鲨在确定其猎物的栖息地使用和介导鲨鱼湾内的间接相互作用方面很重要。

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