Assessing the trophic ecology of top predators across a recolonisation frontier using DNA metabarcoding of diets

Top predator populations, once intensively hunted, are rebounding in size and geographic distribution. The cessation of sealing along coastal Australia and subsequent recovery of Australian Arctocephalus pusillus doriferus and long-nosed A. forsteri fur seals represents a unique opportunity to investigate trophic linkages at a frontier of predator recolonisation. We characterised the diets of both species across 2 locations of recolonisation, one site an established breeding colony, and the other, a new but permanent haul-out site. Using DNA metabarcoding, high taxonomic resolution data on diets was used to inform ecological trait-based analyses across time and location. Australian and long-nosed fur seals consumed 76 and 73 prey taxa, respectively, a prey diversity greater than previously reported. We found unexpected overlap of prey functional traits in the diets of both seal species at the haul-out site, where we observed strong trophic linkages with coastal ecosystems due to the prevalence of benthic, demersal and reef-associated prey. The diets of both seal species at the breeding colony were consistent with foraging patterns observed in the centre of their geographic range regarding diet partitioning between predator species and seasonal trends typically observed. The unexpected differences between sites in this region and the convergence of both predators’ effective ecological roles at the range-edge haul-out site correlate with known differences in seal population densities and demographics at these and other newly recolonised locations. This study provides a baseline for the diets and trophic interactions for recovering fur seal populations and from which to understand the evolving ecology of predator recolonisation.

曾遭受高强度捕猎的顶级捕食者种群，其种群规模与地理分布范围正逐步恢复。澳大利亚沿海地区停止海豹捕猎活动后，澳洲海狗（Arctocephalus pusillus doriferus）与长鼻海狗（A. forsteri）的种群随之恢复，这为研究捕食者重新定殖前沿地带的营养联系提供了独特契机。我们在两处重新定殖区域对两种海狗的食性进行了表征：一处为成熟繁殖群落，另一处为新近形成但长期稳定的上岸休憩点。本研究借助DNA元条形码（DNA metabarcoding）技术获取了高分类学分辨率的食性数据，并以此为基础开展跨时间与空间维度的基于生态功能性状的分析。澳洲海狗与长鼻海狗分别摄食76个与73个猎物类群，其猎物多样性均高于既往研究报道的结果。我们在该上岸休憩点发现，两种海狗的食性中猎物功能性状存在意料之外的重叠；由于底栖、近底栖与依附礁岩的猎物占比颇高，此处与沿海生态系统存在极强的营养联系。两处繁殖群落中两种海狗的食性，与它们地理分布中心区域观测到的捕食者间食性分化模式及典型季节动态特征相符。该区域不同采样点间存在意料之外的食性差异，而两种捕食者在分布边缘上岸休憩点的生态功能趋同，这与已知的两处（及其他新近重新定殖区域）海狗种群密度与种群结构差异相契合。本研究为恢复中的海狗种群的食性与营养相互作用提供了基准数据，同时也为理解捕食者重新定殖过程中的动态生态提供了研究基础。