MaREI Centre, Environmental Research Institute, University College Cork, Cork, Ireland.
School of Biological, Earth & Environmental Sciences, University College Cork, Cork, Ireland.
PLoS One. 2019 Jan 2;14(1):e0209032. doi: 10.1371/journal.pone.0209032. eCollection 2019.
In ecological studies it is often assumed that predator foraging strategies and resource use are geographically and seasonally homogeneous, resulting in relatively static trophic relationships. However, certain centrally placed foragers (e.g. seals) often have terrestrial sites for breeding, resting, and moulting that are geographically distinct, and associated with different habitat types. Therefore, accurate estimations of predator diet at relevant spatial and temporal scales are key to understanding energetic requirements, predator-prey interactions and ecosystem structure. We investigate geographic variation in the diet of grey seals (Halichoerus grypus), a relatively abundant and widely distributed central place forager, to provide insights into geographic variation in resource use. Prey composition was identified using scat samples collected over concurrent timescales and a multivariate approach was used to analyse diet from two contrasting habitats. Regional differences in prey assemblages occurred within all years (2011-2013) and all seasons (ANOSIM, all p<0.05), apart from in winter. Telemetry data were used to identify core foraging areas and habitats most likely associated with scat samples collected at the two haul-out sites. Regional differences in the diet appear to reflect regional differences in the physical habitat features, with seals foraging in deeper waters over sandy substrates showing a higher prevalence of pelagic and bentho-pelagic prey species such as blue whiting and sandeels. Conversely, seals foraging in comparatively shallow waters had a greater contribution of demersal and groundfish species such as cephalopods and flatfish in their diet. We suggest that shallower waters enable seals to spend more time foraging along the benthos while remaining within aerobic dive limits, resulting in more benthic species in the diet. In contrast, the diet of seals hauled-out in areas adjacent to deeper waters indicates that either seals engage in a more pelagic foraging strategy, or that seals can spend less time at the benthos, resulting in comparatively more pelagic prey recovered in the diet. The substantial differences in prey assemblages over a small spatial scale (<300 km) demonstrates the importance of using regionally-specific diet information in ecosystem-based models to better account for different trophic interactions.
在生态研究中，通常假设捕食者的觅食策略和资源利用在地理和季节上是均匀的，从而导致相对稳定的营养关系。然而，某些中心位置的捕食者（例如海豹）通常有繁殖、休息和换羽的陆地场所，这些场所在地理上是不同的，并且与不同的栖息地类型相关。因此，在相关的时空尺度上准确估计捕食者的饮食是理解能量需求、捕食者-猎物相互作用和生态系统结构的关键。我们调查了灰海豹（Halichoerus grypus）饮食的地理变化，灰海豹是一种相对丰富且广泛分布的中心位置捕食者，以深入了解资源利用的地理变化。使用同时收集的粪便样本确定了猎物组成，并使用多元分析方法分析了来自两个对比栖息地的饮食。所有年份（2011-2013 年）和所有季节（除冬季外，所有 ANOSIM，p<0.05）都发生了猎物组合的区域差异。利用遥测数据确定了核心觅食区和最有可能与在两个上岸点收集的粪便样本相关的栖息地。饮食的区域差异似乎反映了物理生境特征的区域差异，在沙质基底的较深水域觅食的海豹表现出更高比例的远洋和底栖-远洋猎物物种，如蓝鳕鱼和沙鳗。相反，在相对较浅的水域觅食的海豹的饮食中，头足类动物和比目鱼等底栖和底层鱼类的比例更高。我们认为，较浅的水域使海豹能够在有氧潜水限制范围内，在海底停留更长时间觅食，从而使饮食中的底栖物种更多。相比之下，在靠近较深水域的区域上岸的海豹的饮食表明，要么海豹采用更远洋的觅食策略，要么海豹在海底停留的时间更少，从而导致饮食中回收的远洋猎物相对更多。在小的空间尺度（<300 公里）上，猎物组合的巨大差异表明，在基于生态系统的模型中使用区域特定的饮食信息非常重要，以便更好地解释不同的营养相互作用。
