Dietary niche variation in an invasive omnivore: the effects of habitat on feral pig (Sus scrofa) resource use in Hawaiʻi

Invasive omnivores may have profound impacts on ecological communities through diet selection, particularly when their functional roles differ from those in their native range. While the threat of feral pigs (Sus scrofa) to native plant communities in Hawai‘i is well known, their trophic dynamics and the drivers of variation in their diet remain understudied. We investigated the feral pig trophic niche on Hawai‘i Island using stable isotopes (13C and 15N) and Bayesian mixing models to identify drivers of variation in resource use. We also reconstructed intra-individual variability for six subsampled individuals to understand temporal variation in resource use and individual diet specialization. Our results revealed feral pigs on Hawai‘i Island exhibit a broad trophic niche characterized by diverse diets, with substantial overlap in resource use across districts and habitats. Differences in dietary composition in the transition from forest to open habitat were driven primarily by a decline in invertebrates and an increasing reliance on resources enriched in 15N, which may reflect a shift in protein sources with habitat. Pigs in forested areas exhibited a smaller trophic niche than those in open habitats, largely driven by differences in feeding strategies and resource availability. Diets for subsampled individuals varied little, suggesting feral pig resource-use strategies in Hawai‘i tend to be relatively stable through time. Individual niche-width was relatively narrow compared to that of feral pigs in Hawai‘i at large, indicating the relatively wide feral pig dietary niche is characterized by substantial intraspecific diet specialization, likely as a result of strong intraspecific competition. Understanding the drivers of feral pig resource use offers key information for management strategies aimed at mitigating their ecological impacts in imperiled systems like Hawai‘i.

Methods
Resources were collected around Hawai‘i island in the districts noted in the dataset raw.data_sources.csv. All tail hair samples were cleaned using 2:1 chloroform:methanol solution, sectioned, and 13C and 15N were quantified using accelerator mass spectrometry at the University of New Mexico’s Stable Isotope Laboratory (Albuquerque, NM). 3-mm sections of the most recent hair (closest to the skin) was used for raw.data_sampled.indiviuduals.csv. Hairs from six individuals were subsampled 12 - 16 times in the data file raw.data_subsampled.individuals.csv.

入侵性杂食动物可能通过食物选择对生态群落产生深远影响，尤其是当其功能角色与其原生分布范围中的功能角色存在差异时。尽管野猪（Sus scrofa）对夏威夷本土植物群落的威胁已广为人知，但它们的营养动态以及饮食差异的驱动因素仍未得到充分研究。我们利用稳定同位素（stable isotopes，¹³C与¹⁵N）和贝叶斯混合模型（Bayesian mixing models），对夏威夷岛上的野猪营养生态位（trophic niche）展开研究，以明确资源利用差异的驱动因素。此外，我们还对6个采样个体进行了个体内变异性重建，以解析资源利用的时间变化与个体饮食特化情况。

研究结果显示，夏威夷岛上的野猪拥有宽泛的营养生态位，表现出多样化的饮食结构，不同区域与生境的野猪在资源利用上存在显著重叠。从森林到开阔生境的过渡过程中，饮食组成的差异主要由无脊椎动物占比下降，以及对¹⁵N富集资源的依赖度提升所驱动，这或许反映了随生境变化的蛋白质来源转变。森林生境中的野猪营养生态位较开阔生境中的野猪更窄，这主要由取食策略与资源可获得性的差异所导致。对采样个体的饮食分析显示其差异极小，表明夏威夷野猪的资源利用策略在时间维度上相对稳定。相较于整体种群的营养生态位，单个个体的生态位宽度相对较窄，这说明野猪宽泛的整体饮食生态位实则伴随显著的种内饮食特化，这一现象可能源于强烈的种内竞争。明确野猪资源利用的驱动因素，可为旨在缓解其在夏威夷等濒危生态系统中生态影响的管理策略提供关键信息。

研究方法
本研究的样本采集工作围绕夏威夷岛展开，采样区域信息详见数据集文件raw.data_sources.csv。所有尾毛样本均采用2:1氯仿:甲醇溶液进行清洁处理，随后进行切片，并于新墨西哥大学稳定同位素实验室（Albuquerque, NM）利用加速器质谱法（accelerator mass spectrometry）对¹³C与¹⁵N进行定量分析。本研究选取最接近皮肤的最新生长毛发的3mm切片，相关数据详见raw.data_sampled.indiviuduals.csv。在raw.data_subsampled.individuals.csv数据文件中，我们对6个个体的毛发进行了12至16次的重复采样。