Wandering Albatross observed and simulated GPS tracks from Crozet and Marion islands (2016-2019)

Sexual competition is increasingly recognized as an important
selective pressure driving species distributions. However, few studies
have investigated the relative importance of inter-
vs. intrapopulation competition in relation to habitat
availability and selection. To explain spatial segregation between sexes
that often occurs in non-territorial and central place foragers, such as
seabirds, two hypotheses are commonly used. The ‘competitive exclusion’
hypothesis states that dominant individuals should exclude subordinate
individuals through direct competition whereas the ’niche
divergence’ hypothesis states that segregation occurs due to past
competition and habitat specialization. We tested
these hypotheses in two populations of an extreme wide-ranging
and sexually dimorphic seabird, investigating the
relative role of intrapopulation and interpopulation
competition in influencing sex-specific distribution and habitat
preferences. Using GPS loggers, we tracked 192 wandering
albatrosses Diomedea exulans during four consecutive years
(2016-2019), from two neighbouring populations in the Southern Ocean
(Prince Edward and Crozet archipelagos). We simulated pseudo-tracks to
create a null spatial distribution and used Kernel Density Estimates (KDE)
and Resource Selection Functions (RSF) to distinguish the relative
importance of within vs. between population competition. KDE
showed that only intrapopulation sexual segregation was
significant for each monitoring year, and that tracks between the
two colonies resulted in greater overlap than expected from the null
distribution, especially for the females. RSF confirmed these results
and highlighted key at-sea foraging areas, even if the estimated
of at-sea densities were extremely low. These differences
in selected areas between sites and sexes were, however,
associated with high interannual variability in habitat
preferences, with no clear specific preferences per site and sex. Our
results suggest that even with low at-sea population densities, historic
intrapopulation competition in wide-ranging seabirds may have led to
sexual dimorphism and niche specialization, favouring the ‘niche
divergence’ hypothesis. In this study, we provide a protocol to
study competition within as well as between populations of central place
foragers. This is relevant for understanding their distribution patterns
and population regulation, which could potentially improve management of
threatened populations.

性竞争（Sexual competition）日益被视为驱动物种分布格局形成的重要选择压力。然而，鲜有研究探讨种群间与种群内竞争在生境可获得性与生境选择中的相对重要性。为解释非领地性中心地觅食者（如海鸟）中常见的两性空间分离现象，学界通常采用两类假说：竞争排除假说（Competitive Exclusion Hypothesis）指出，优势个体可通过直接竞争排挤弱势个体；而生态位分化假说（Niche Divergence Hypothesis）则提出，空间分离源于既往竞争与生境特化。本研究以一种广布范围极广且具显著性二态性的海鸟——漂泊信天翁（Wandering Albatross，*Diomedea exulans*）为研究对象，选取其位于南大洋爱德华王子群岛与克罗泽群岛的两个邻近种群，于2016-2019年连续四年借助GPS记录仪追踪了192只个体，探究种群内与种群间竞争在塑造两性分布格局与生境偏好中的相对作用。我们通过模拟伪轨迹构建零空间分布模型，并结合核密度估计（Kernel Density Estimates, KDE）与资源选择函数（Resource Selection Functions, RSF），以区分种群内与种群间竞争的相对重要性。核密度估计结果显示，仅在各监测年度内，种群内的两性分离现象均具有统计学显著性；且两个繁殖种群间的个体活动轨迹重叠度高于零分布模型的预期值，雌性个体的重叠情况尤为显著。资源选择函数分析验证了上述结果，并识别出关键的海上觅食区域，尽管海上种群密度的估算值极低。不过，不同种群与两性间的觅食区域选择差异，与生境偏好的高年际变异性相关，且未呈现出明确的种群与两性专属偏好。本研究结果表明，即便海上种群密度较低，广布海鸟的历史种群内竞争或已推动了性二态性与生态位特化的演化，这一发现支持生态位分化假说。本研究还为探究中心地觅食者的种群内与种群间竞争提供了一套研究范式，这有助于理解其分布格局与种群调控机制，进而有望为受威胁种群的保护管理提供支撑。