Context‐dependent effects of shifting large herbivore assemblages on plant structure and diversity
Context‐dependent effects of shifting large herbivore assemblages on plant structure and diversity
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DOI：
10.1111/1365-2745.13871
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发表时间：
2022-03
影响因子：
5.5
通讯作者：
D. Orr;A. Bui;M. Klope;I. McCullough;Michelle J. Lee;Carina I Motta;I. Mayorga;Kelli Konicek;H. Young
中科院分区：
文献类型：
--
作者：
D. Orr;A. Bui;M. Klope;I. McCullough;Michelle J. Lee;Carina I Motta;I. Mayorga;Kelli Konicek;H. Young
尽管人们广泛认识到人类驱动的变化在大型食草动物群落中的重要性--包括野生动物的减少和牲畜的增加--但我们对这些变化对植物群落的影响的认识仍然存在很大差距，特别是在与气候同时变化的情况下。同时考虑这些突出的全球变化形式使我们能够更好地了解在现实世界条件下对稀树草原植被结构和多样性的控制。我们使用完全和半透水的草食动物封闭物进行了野外实验，以探索只有野生草食动物、有牛和野生草食动物以及没有大型草食动物的地点之间植物群落的差异。为了了解不同气候背景下影响的变化，这项实验在加利福尼亚州沿地形气候梯度的三个地点重复进行。关键的是，这是第一次在一个单独的对照实验中比较牛和野生动物对环境梯度的影响。植被结构对草食动物处理的响应强烈，与气候无关。相对于野生动物的孤立影响，排除所有大型食草动物通常增加了与覆盖物和地上生物量有关的结构成分，而牛的加入导致植被覆盖率、凋落物、遮荫和现存量减少。此外，野生动物对植物多样性具有一致的中性或正向影响，而家畜增加的影响取决于背景。黄牛在低干旱时表现为中性到强烈的负效应，而在高干旱时表现为正效应。这些结果表明：(A)草食动物效应可以盖过气候对植被结构的影响，(B)牛的添加可以对多样性产生不同的影响，(C)草食动物对多样性的影响是受气候调节的。综合。我们的结果表明，植物群落在有蹄类草食动物组合的两种现实形式变化-家畜增加和大量草食动物损失-之间发生了非常明显的变化，特别是对植物多样性的反应，这些反应因气候背景而异。这一发现对植物生物多样性的管理和保护具有重要影响，因为地球上四分之一以上的土地被管理为牲畜，而且全球气候制度正在发生变化。
Despite wide recognition of the importance of anthropogenically driven changes in large herbivore communities—including both declines in wildlife and increases in livestock—there remain large gaps in our knowledge about the impacts of these changes on plant communities, particularly when combined with concurrent changes in climate. Considering these prominent forms of global change in tandem enables us to better understand controls on savanna vegetation structure and diversity under real‐world conditions. We conducted a field experiment using complete and semi‐permeable herbivore exclosures to explore the difference in plant communities among sites with wild herbivores only, with cattle in addition to wild herbivores, and with no large herbivores. To understand variation in effects across climatic contexts, the experiment was replicated at three locations along a topoclimatic gradient in California. Critically, this is the first such experiment to compare cattle and wildlife impacts along an environmental gradient within a single controlled experiment. Vegetation structure responded strongly to herbivore treatment regardless of climate. Relative to the isolated effects of wildlife, exclusion of all large herbivores generally increased structural components related to cover and above‐ground biomass while the addition of cattle led to reductions in vegetation cover, litter, shading and standing biomass. Furthermore, wildlife had a consistent neutral or positive effect on plant diversity, while the effect of livestock addition was context dependent. Cattle had a neutral to strongly negative effect at low aridity, but a positive effect at high aridity. These results suggest that (a) herbivore effects can override climate effects on vegetation structure, (b) cattle addition can drive different effects on diversity and (c) herbivore effects on diversity are modulated by climate. Synthesis. Our results illustrate very distinctive shifts in plant communities between two realistic forms of change in ungulate herbivore assemblages—livestock addition and large herbivore losses—particularly for plant diversity responses, and that these responses vary across climatic contexts. This finding has important implications for the management and protection of plant biodiversity given that over a quarter of the Earth's land area is managed for livestock and climate regimes are changing globally.