Inter‐ and intrasex habitat partitioning in the highly dimorphic southern elephant seal,Ecology and Evolution

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Inter‐ and intrasex habitat partitioning in the highly dimorphic southern elephant seal
Ecology and Evolution ( IF 2.3 ) Pub Date : 2021-01-29 , DOI: 10.1002/ece3.7147
Mark A Hindell ₁ , Clive R McMahon _{1,

2,

3} , Ian Jonsen ₃ , Robert Harcourt _{2,

3} , Fernando Arce ₁ , Christophe Guinet ₄

Affiliation

Partitioning resources is a key mechanism for avoiding intraspecific competition and maximizing individual energy gain. However, in sexually dimorphic species it is difficult to discern if partitioning is due to competition or the different resource needs of morphologically distinct individuals. In the highly dimorphic southern elephant seal, there are intersexual differences in habitat use; at Iles Kerguelen, males predominantly use shelf waters, while females use deeper oceanic waters. There are equally marked intrasexual differences, with some males using the nearby Kerguelen Plateau, and others using the much more distant Antarctic continental shelf (~2,000 km away). We used this combination of inter and intrasexual behavior to test two hypotheses regarding habitat partitioning in highly dimorphic species. (a) that intersexual differences in habitat use will not appear until the seals diverge in body size and (b) that some habitats have higher rates of energy return than others. In particular, that the Antarctic shelf would provide higher energy returns than the Kerguelen Shelf, to offset the greater cost of travel. We quantified the habitat use of 187 southern elephant seals (102 adult females and 85 subadult males). The seals in the two groups were the same size (~2.4 m) removing the confounding effect of body size. We found that the intersexual differences in habitat use existed before the divergence in body size. Also, we found that the amount of energy gained was the same in all of the major habitats. This suggests that the use of shelf habitats by males is innate, and a trade‐off between the need to access the large benthic prey available on shelf waters, against the higher risk of predation there. Intrasexual differences in habitat use are another trade‐off; although there are fewer predators on the Antarctic shelf, it is subject to considerable interannual fluctuations in sea‐ice extent. In contrast, the Kerguelen Plateau presents more consistent foraging opportunities, but contains higher levels of predation. Habitat partitioning in this highly dimorphic species is therefore the result of complex interplay of life history strategies, environmental conditions and predation pressure.

中文翻译：

高度二态性南象海豹的性间和性内栖息地划分

资源分配是避免种内竞争和最大化个体能量增益的关键机制。然而，在性二态性物种中，很难辨别分配是由于竞争还是由于形态不同个体的不同资源需求。在高度二态性的南象海豹中，栖息地利用存在两性差异。在凯尔盖朗岛，雄性主要使用陆架水域，而雌性则使用更深的海洋水域。两性之间也存在同样明显的差异，一些雄性使用附近的凯尔盖朗高原，而其他雄性则使用更遥远的南极大陆架（约 2,000 公里远）。我们利用这种性间和性内行为的组合来检验关于高度二态性物种的栖息地划分的两个假设。 (a) 在海豹的体型出现差异之前，栖息地利用的两性差异才会出现；(b) 一些栖息地的能量回报率高于其他栖息地。特别是，南极大陆架将比凯尔盖朗大陆架提供更高的能量回报，以抵消更大的旅行成本。我们量化了 187 只南象海豹（102 只成年雌性和 85 只亚成年雄性）的栖息地利用情况。两组海豹的尺寸相同（~2.4 m），消除了体型尺寸的混杂影响。我们发现，栖息地利用方面的两性差异在体型差异之前就已经存在。此外，我们发现所有主要栖息地获得的能量都是相同的。这表明雄性对架子栖息地的使用是与生俱来的，并且需要在获取架子水域上可用的大型底栖猎物的需要与那里较高的捕食风险之间进行权衡。栖息地利用方面的两性差异是另一个权衡。尽管南极大陆架上的捕食者较少，但其海冰范围却受到相当大的年际波动的影响。相比之下，凯尔盖朗高原提供了更稳定的觅食机会，但捕食程度更高。因此，这种高度二态性物种的栖息地划分是生活史策略、环境条件和捕食压力复杂相互作用的结果。

更新日期：2021-02-15

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