Jones O E, Beckett H, Abraham A J, Makunga N P, Midgley G F
School for Climate Studies Stellenbosch University Matieland South Africa.
Centre for Ecological Dynamics in a Novel Biosphere (ECONOVO), Section of Ecoinformatics and Biodiversity, Department of Biology Aarhus University Aarhus C Denmark.
Ecol Evol. 2025 Sep 1;15(9):e71951. doi: 10.1002/ece3.71951. eCollection 2025 Sep.
Megaherbivores are typically regarded as agents of top-down control, limiting woody encroachment through destructive foraging. Yet they also possess traits and engage in behaviours that facilitate plant success. For example, megaherbivores can act as effective endozoochorous seed dispersers. However, studies on facilitative roles are heavily biased towards the African savanna elephant (), with little attention paid to other species or to effects beyond germination, across early ontogenic stages. The African black rhinoceros (), an obligate browser that exhibits frugivory and defecates in fixed dung middens, may offer ecologically distinct dispersal services. We conducted controlled experiments to test whether black rhino interactions with , a leguminous tree of ecological importance in arid savannas, enhance germination, early seedling development or seedling resilience to herbivory. Germination was compared among dung-derived seeds, untreated controls and chemically scarified seeds. Seedling growth was assessed in dung versus sand and under simulated black rhino herbivory. Dung-derived seeds germinated most steadily and produced the highest cumulative germination (+40%) over the longest period (+13 days). Growth trials revealed that dung substrates did not enhance initial growth. Rather, seedlings being older conferred greater resilience to biomass loss than exposure to different substrate conditions. Our results provide the first experimental evidence of an apparent mutualism between black rhino and . This relationship is not driven by enhanced seedling development through legacy effects of gut passage, nor by dung conditions, as expected. Instead, it stems from gut passage effects on germination. In addition to increasing total germination, gut passage accelerates germination and extends the germination period, producing a seedling cohort with both older individuals and greater age variation-a population structure that may enhance persistence beyond the germination bottleneck. This research supports a more nuanced view of megaherbivores as both disturbance agents and mutualists in arid ecosystems.
巨型食草动物通常被视为自上而下控制的推动者，通过破坏性觅食限制木本植物的入侵。然而，它们也具有促进植物成功的特征和行为。例如，巨型食草动物可以作为有效的内寄生种子传播者。然而，关于促进作用的研究严重偏向于非洲草原象（），很少关注其他物种或发芽以外的早期个体发育阶段的影响。非洲黑犀牛（）是一种专性食叶动物，表现出食果性并在固定的粪堆中排便，可能提供生态上独特的传播服务。我们进行了对照实验，以测试黑犀牛与干旱稀树草原生态重要的豆科树木之间的相互作用是否能提高发芽率、早期幼苗发育或幼苗对食草动物的恢复力。比较了粪便来源的种子、未处理的对照种子和化学划痕种子的发芽情况。在粪便与沙子中以及模拟黑犀牛食草的情况下评估幼苗生长。粪便来源的种子发芽最稳定，在最长时期（+13天）内产生最高的累积发芽率（+40%）。生长试验表明，粪便基质并没有促进初始生长。相反，幼苗年龄越大，对生物量损失的恢复力比暴露于不同基质条件下更强。我们的结果提供了黑犀牛与之间明显互利共生的首个实验证据。这种关系不是由肠道通过的遗留效应促进幼苗发育驱动的，也不是如预期的由粪便条件驱动的。相反，它源于肠道通过对发芽的影响。除了增加总发芽率外，肠道通过还加速发芽并延长发芽期，产生一个既有年龄较大个体又有较大年龄差异的幼苗群体——这种种群结构可能增强在发芽瓶颈之后的持久性。这项研究支持了一种更细致入微的观点，即巨型食草动物在干旱生态系统中既是干扰因素又是共生者。
