Data from: DNA metabarcoding illuminates dietary niche partitioning by African large herbivores

Niche partitioning facilitates species coexistence in a world of limited resources, thereby enriching biodiversity. For decades, biologists have sought to understand how diverse assemblages of large mammalian herbivores (LMH) partition food resources. Several complementary mechanisms have been identified, including differential consumption of grasses versus nongrasses and spatiotemporal stratification in use of different parts of the same plant. However, the extent to which LMH partition food-plant species is largely unknown because comprehensive species-level identification is prohibitively difficult with traditional methods. We used DNA metabarcoding to quantify diet breadth, composition, and overlap for seven abundant LMH species (six wild, one domestic) in semiarid African savanna. These species ranged from almost-exclusive grazers to almost-exclusive browsers: Grass consumption inferred from mean sequence relative read abundance (RRA) ranged from >99% (plains zebra) to <1% (dik-dik). Grass RRA was highly correlated with isotopic estimates of % grass consumption, indicating that RRA conveys reliable quantitative information about consumption. Dietary overlap was greatest between species that were similar in body size and proportional grass consumption. Nonetheless, diet composition differed between all species—even pairs of grazers matched in size, digestive physiology, and location—and dietary similarity was sometimes greater across grazing and browsing guilds than within them. Such taxonomically fine-grained diet partitioning suggests that coarse trophic categorizations may generate misleading conclusions about competition and coexistence in LMH assemblages, and that LMH diversity may be more tightly linked to plant diversity than is currently recognized.

生态位分隔（niche partitioning）是有限资源环境中物种共存的核心机制，亦是生物多样性得以维持与提升的重要动因。数十年来，生态学家一直致力于解析多样的大型哺乳动物食草动物（large mammalian herbivores，以下简称LMH）类群如何通过生态位分隔实现食物资源的分配利用。目前已明确多种互补共存的食性分隔机制，包括对草本与非草本植物的取食偏好差异，以及对同一植株不同部位的时空利用分层模式。然而，LMH对食物植物物种的生态位分隔程度仍鲜为人知，这是因为传统方法难以实现全面的物种级鉴定，其成本与难度均难以承受。本研究利用DNA宏条形码（DNA metabarcoding）技术，对非洲半干旱稀树草原中7种常见LMH类群（6种野生、1种家养）的食性广度、食性组成与种间食性重叠度进行了定量分析。这些类群的取食策略涵盖了从几乎专食草本的草食者到几乎专食非草本植物的食叶者的完整谱系：基于平均相对序列读丰度（relative read abundance，以下简称RRA）推算的草本取食占比，从平原斑马的99%以上到犬羚的1%以下不等。基于RRA的草本取食占比与基于同位素技术推算的草本取食百分比呈现显著相关，这表明RRA能够提供可靠的取食定量信息。体型与草本取食占比相近的物种间，食性重叠度最高。尽管如此，所有物种的食性组成均存在显著差异——即便体型、消化生理与栖息生境均高度匹配的成对草食者亦是如此；且跨草食与食叶功能群的食性相似性，有时反而高于同一功能群内部。这种具备精细分类学分辨率的食性生态位分隔模式表明，对LMH类群的粗粒度营养级分类，可能会在竞争与共存机制的解读中产生误导性结论；同时，LMH多样性与植物多样性的关联，或许比当前认知中更为紧密。