The past, present, and future of herbivore impacts on savanna vegetation
The past, present, and future of herbivore impacts on savanna vegetation
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草食动物对稀树草原植被影响的过去、现在和未来
DOI：
10.1111/1365-2745.13685
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发表时间：
2021-06
影响因子：
5.5
通讯作者：
A. C. Staver;Joel O. Abraham;G. Hempson;A. Karp;J. Faith
中科院分区：
文献类型：
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作者：
A. C. Staver;Joel O. Abraham;G. Hempson;A. Karp;J. Faith
草食是稀树草原植被结构的关键过程，特别是在非洲，大型哺乳动物草食群落保持完整。排除实验一致表明，草食动物影响稀树草原植被，但效应大小的变化难以解释，限制了我们对过去、现在和未来草食动物在稀树草原生态系统中的作用的理解。对草食动物排除后的植被响应的综合分析表明，草食使整个非洲稀树草原的草丰度减少了57.0%，树木丰度减少了30.6%。草食动物排斥效应的大小与草食动物的丰度成正比：草食动物越多，草食动物越多，草食动物的响应越大；然而，现有的实验集中在半干旱的稀树草原（400-800毫米降雨量），土壤数据大多缺乏，这使得解开环境约束成为未来研究的挑战和重点。观察到的食草动物影响比现有的基于消费模型的估计大2.1倍。野生动物的代谢率可能比通常用于估计消耗的要高，这为调和估计的草食动物消耗与观察到的草食动物影响提供了一个明确的途径。植物-土壤反馈、植物群落组成和草食的物候或人口时间也可能影响植被生产力，从而放大草食动物的影响。因为食草动物的丰度如此接近地预测植被的影响，食草动物丰度随时间的变化很可能预测它们的影响的过去和未来。非洲的食草动物多样性已经从100万年前的峰值下降，野生食草动物的丰度也在历史上下降，这表明过去的放牧可能比今天的影响更大。目前对野生动物的影响主要是由小型混合饲料动物主导的，这种情况可能会持续到未来，但自上而下的控制程度也可能取决于气候、火灾和大气二氧化碳的变化。合成。草食动物的生物量决定了它们对稀树草原植被的影响程度，基于直接观察的效应大小超过了非洲稀树草原上现有的模型估计。研究结果表明，草食动物对生态系统有重大影响，并使我们能够基于证据提出草食动物对稀树草原植被过去和未来影响的假设。
Herbivory is a key process structuring vegetation in savannas, especially in Africa where large mammal herbivore communities remain intact. Exclusion experiments consistently show that herbivores impact savanna vegetation, but effect size variation has resisted explanation, limiting our understanding of the past, present and future roles of herbivory in savanna ecosystems. Synthesis of vegetation responses to herbivore exclusion shows that herbivory decreased grass abundance by 57.0% and tree abundance by 30.6% across African savannas. The magnitude of herbivore exclusion effects scaled with herbivore abundance: more grazing herbivores resulted in larger grass responses and more browsing herbivores in larger tree responses. However, existing experiments are concentrated in semi‐arid savannas (400–800‐mm rainfall) and soils data are mostly lacking, which makes disentangling environmental constraints a challenge and priority for future research. Observed herbivore impacts were ~2.1× larger than existing estimates modelled based on consumption. Wildlife metabolic rates may be higher than are usually used for estimating consumption, which offers one clear avenue for reconciling estimated herbivore consumption with observed herbivore impacts. Plant‐soil feedbacks, plant community composition, and the phenological or demographic timing of herbivory may also influence vegetation productivity, thereby magnifying herbivore impacts. Because herbivore abundance so closely predicts vegetation impact, changes in herbivore abundance through time are likely predictive of the past and future of their impacts. Grazer diversity in Africa has declined from its peak 1 million years ago and wild grazer abundance has declined historically, suggesting that grazing likely had larger impacts in the past than it does today. Current wildlife impacts are dominated by small‐bodied mixed feeders, which will likely continue into the future, but the magnitude of top‐down control may also depend on changing climate, fire and atmospheric CO2. Synthesis. Herbivore biomass determines the magnitude of their impacts on savanna vegetation, with effect sizes based on direct observation that outstrip existing modelled estimates across African savannas. Findings suggest substantial ecosystem impacts of herbivory and allow us to generate evidence‐based hypotheses of the past and future impacts of herbivores on savanna vegetation.