Megaherbivores (adult body mass > 1000 kg) are suggested to disproportionately shape ecosystem and Earth system functioning. We systematically reviewed the empirical basis for this general thesis and for the more specific hypotheses that 1) megaherbivores have disproportionately larger effects on Earth system functioning than their smaller counterparts, 2) this is true for all extant megaherbivore species and 3) their effects vary along environmental gradients. We furthermore explored possible biases in our understanding of megaherbivore impacts. We found that there are too few studies to quantitatively evaluate the general thesis or any of the hypotheses for all but the African savanna elephant. Following this finding, we performed a qualitative vote counting analysis. Our synthesis of this analysis suggests that megaherbivores can elicit strong impacts on, for example, vegetation structure and biodiversity, and all the elephant species promote seed dispersal. We were, however, unable to evaluate whether these effects are disproportionate to smaller large herbivores. Although environmental conditions can mediate megaherbivore impact, few studies quantified the effect of rainfall or soil fertility on megaherbivore impacts, precluding prediction of megaherbivore effects on the Earth system, particularly under future climates. Moreover, our review highlights major taxonomic, thematic and geographic biases in our understanding of megaherbivore effects. Most of the studies focused on African savanna elephant impacts on vegetation structure and biodiversity, with other megaherbivores and Earth system functions comparatively neglected. Studies were also biased towards semi-arid and relatively fertile systems, with the arid, high-rainfall and/or nutrient-poor parts of the megaherbivores' distribution ranges largely unrepresented. Our findings highlight that the empirical basis of our understanding of the ecological effects of extant megaherbivores is still limited for all species, except the African savanna elephant, and that our current understanding is biased towards certain environmental and geographic areas. We further outline a detailed, urgently needed avenue for future research.

中文翻译：

---

巨型食草动物对生态系统和地球系统功能的影响：科学现状

巨型食草动物（成年体重 > 1000 kg）被认为会不成比例地塑造生态系统和地球系统的功能。我们系统地回顾了这个一般性论文和更具体的假设的经验基础，即 1) 巨型食草动物对地球系统功能的影响比它们较小的同类动物要大得多，2) 这对于所有现存的巨型食草动物物种都是如此，3) 它们的影响随着环境梯度。我们进一步探讨了我们对巨型食草动物影响的理解中可能存在的偏见。我们发现，除了非洲稀树草原象之外，很少有研究能够定量评估一般论点或任何假设。根据这一发现，我们进行了定性计票分析。我们对这一分析的综合表明，大型食草动物可以对植被结构和生物多样性等产生强烈影响，并且所有大象物种都会促进种子传播。然而，我们无法评估这些影响是否与较小的大型食草动物不成比例。尽管环境条件可以调节大型食草动物的影响，但很少有研究量化降雨或土壤肥力对大型食草动物影响的影响，从而无法预测大型食草动物对地球系统的影响，特别是在未来气候下。此外，我们的评论强调了我们对巨型食草动物影响的主要分类学、主题和地理偏见。大多数研究集中在非洲稀树草原大象对植被结构和生物多样性的影响上，与其他大型食草动物和地球系统功能相对被忽视。研究也偏向于半干旱和相对肥沃的系统，大型食草动物分布范围的干旱、高降雨量和/或营养贫乏的部分基本上没有代表性。我们的研究结果强调，我们对现存巨型食草动物生态影响的理解的经验基础对于所有物种仍然是有限的，除了非洲大草原象，而且我们目前的理解偏向于某些环境和地理区域。我们进一步概述了一个详细的、迫切需要的未来研究途径。我们的研究结果强调，我们对现存巨型食草动物生态影响的理解的经验基础对于所有物种仍然是有限的，除了非洲大草原象，而且我们目前的理解偏向于某些环境和地理区域。我们进一步概述了一个详细的、迫切需要的未来研究途径。我们的研究结果强调，我们对现存巨型食草动物生态影响的理解的经验基础对于所有物种仍然是有限的，除了非洲大草原象，而且我们目前的理解偏向于某些环境和地理区域。我们进一步概述了一个详细的、迫切需要的未来研究途径。