Large herbivores suppress liana infestation in an African savanna
Large herbivores suppress liana infestation in an African savanna
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DOI：
10.1073/pnas.2101676118
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发表时间：
2021-09
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影响因子：
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通讯作者：
Tyler C. Coverdale;R. D. O'Connell;Matthew C. Hutchinson;Amanda G. Savagian;Tyler R. Kartzinel;T. Palmer;J. Goheen;D. Augustine;M. Sankaran;C. Tarnita;R. Pringle
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作者：
Tyler C. Coverdale;R. D. O'Connell;Matthew C. Hutchinson;Amanda G. Savagian;Tyler R. Kartzinel;T. Palmer;J. Goheen;D. Augustine;M. Sankaran;C. Tarnita;R. Pringle
意义野生巨型动物的减少预计将改变生态系统，并已知会影响非洲大草原的树木-草平衡，但大型食草动物对藤本植物的影响尚不清楚。使用饮食分析，长期的封闭实验，和小规模的操作，我们表明，藤本植物感染后迅速发生的大型食草动物和抑制树木的生长和繁殖的损失。我们从理论上表明，长期没有食草动物可能会产生一个藤本植物占主导地位的替代状态，但实验和理论结果表明，食草动物的重新引入可以扭转地方性的侵扰，即使几十年后。我们发现，在野生草食动物物种之间，野生动物和牲畜之间的低功能冗余。我们的研究结果表明，不同的大型草食动物组合促进恢复力和鲁棒性的热带稀树草原藤本植物入侵。非洲稀树草原是各种大型哺乳动物群落的最后据点，稀树草原生态学的一个主要焦点是了解这些动物如何影响树木和草的相对丰度。然而，热带稀树草原支持不同的植物生命形式，和人类引起的变化，在大型草食动物的组合，野生动物种群下降和他们的流离失所的牲畜，可能会导致意想不到的变化，在植物群落组成。我们调查了食草动物如何影响藤本植物（木本藤本植物）的流行及其对东非稀树草原树木的影响。虽然稀有（<2%的树冠面积）和有毒乳胶的保护，占主导地位的藤本植物，Cynanchum viminale（夹竹桃科），被15个野生大型草食动物物种吃掉，并在实验食堂试验中被本地浏览器大量消耗。相反，家养的有蹄类动物很少吃藤本植物。当我们实验排除所有大型食草动物的8至17年（模拟灭绝）的时期，藤本植物的丰度急剧增加，高达75%的树木出没。分段排除不同大小的食草动物揭示功能互补的大小类抑制藤本植物。藤本植物感染减少了树木的生长和繁殖，但草食动物迅速清除藤本植物从树木后，拆除18岁的围篱（模拟野化）。藤本植物传染的一个简单模型表明，如果没有食草动物，长期平衡可能是地方性的（藤本植物树共存）或所有的藤本植物替代稳定状态。我们的结论是，野生大型食草动物种群的持续下降将破坏许多非洲稀树草原的结构和功能的方式，很少受到关注，并可能不会减轻取代野生动物与牲畜。
Significance Declines of wild megafauna are expected to transform ecosystems and are known to influence tree–grass balance in African savannas, but the effects of large herbivores on lianas are unknown. Using diet analysis, long-term exclosure experiments, and smaller-scale manipulations, we show that liana infestation occurred rapidly after the loss of large herbivores and suppressed tree growth and reproduction. We show theoretically that extended absence of herbivores could potentially generate a liana-dominated alternative state—but both experimental and theoretical results indicate that herbivore reintroduction can reverse endemic infestation, even after decades. We found low functional redundancy among wild herbivore species and between wildlife and livestock. Our results suggest that diverse large-herbivore assemblages promote resilience and robustness of savannas to liana encroachment. African savannas are the last stronghold of diverse large-mammal communities, and a major focus of savanna ecology is to understand how these animals affect the relative abundance of trees and grasses. However, savannas support diverse plant life-forms, and human-induced changes in large-herbivore assemblages—declining wildlife populations and their displacement by livestock—may cause unexpected shifts in plant community composition. We investigated how herbivory affects the prevalence of lianas (woody vines) and their impact on trees in an East African savanna. Although scarce (<2% of tree canopy area) and defended by toxic latex, the dominant liana, Cynanchum viminale (Apocynaceae), was eaten by 15 wild large-herbivore species and was consumed in bulk by native browsers during experimental cafeteria trials. In contrast, domesticated ungulates rarely ate lianas. When we experimentally excluded all large herbivores for periods of 8 to 17 y (simulating extirpation), liana abundance increased dramatically, with up to 75% of trees infested. Piecewise exclusion of different-sized herbivores revealed functional complementarity among size classes in suppressing lianas. Liana infestation reduced tree growth and reproduction, but herbivores quickly cleared lianas from trees after the removal of 18-y-old exclosure fences (simulating rewilding). A simple model of liana contagion showed that, without herbivores, the long-term equilibrium could be either endemic (liana–tree coexistence) or an all-liana alternative stable state. We conclude that ongoing declines of wild large-herbivore populations will disrupt the structure and functioning of many African savannas in ways that have received little attention and that may not be mitigated by replacing wildlife with livestock.