COLLABORATIVE RESEARCH: Landscape-scale consequences of mutualism disruption: invasive ants threaten a widespread ant-plant mutualism in East Africa

合作研究：互利共生破坏的景观规模后果：入侵蚂蚁威胁东非广泛的蚂蚁-植物互利共生

• 批准号: 1556728
• 负责人: Jacob Goheen
• 金额: $ 64.38万
• 依托单位: University of Wyoming
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2016
• 资助国家: 美国
• 起止时间: 2016-05-01 至 2021-04-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1556728&HistoricalAwards=false
• 关键词: COLLABORATIVE; RESEARCH; Landscape; scale; consequences

Throughout the natural world, one can find pairs of species living together and providing services for one another to their mutual benefit. These species interactions are called mutualisms, and they are thought to maintain much of the world's biodiversity. Mutualisms are also the basis for important ecosystem services like seed dispersal, pollination, and nutrient cycling. But what happens when an invasive species displaces one of the species partners in a mutualism? That is the question this project will address in the savannas of Kenya, where an invasive ant species is displacing the native ants that live on acacia trees. Native ants aggressively defend trees by attacking elephants and other herbivores that eat trees; in exchange, trees provide food (sugary nectar) and shelter (swollen thorns) for the ants. In contrast, an invasive species, big-headed ants, kill native ants but do not defend trees. Without their native bodyguards, trees are being eaten and killed by elephants more frequently. This project will assess the rate and extent of tree loss associated with the big-headed ant species invasion. Because many species of wild herbivores, including endangered black rhinos, rely on trees in one way or another, this project also aims to understand how tree loss affects habitat for wildlife. This research provides a unique opportunity to assess the domino effects of a critical species mutualism breakdown in a landscape with an abundance of elephants, giraffes, and other iconic species of large mammals. This project will test the hypothesis that the cascading effects of the invasive ant species P. megacephala on the foundational mutualism between Acacia drepanolobium and native ants are context-dependent. In savannas invaded by P. megacephala, elephants are expected to reduce tree cover, thereby lowering soil and plant nitrogen (N) and negatively affecting forage and habitat quality for wildlife (since A. drepanolobium is an N-fixer). In contrast, where elephants are absent, P. megacephala invasion should accelerate tree growth, as P. megacephala does not induce nectar production and thus may reduce metabolic costs to host plants. Over the long-term, this mutualism breakdown is predicted to lead to higher tree cover and soil N in invaded areas. This project will (1) quantify the effects of native versus invasive ants on growth, N-fixation, reproduction and biomass of trees in the presence and absence of wild herbivores, especially elephants; (2) use demographic models to project tree population growth rates; (3) use remote sensing to assess the rate of spread of the P. megacephala invasion in both wildlife-present and wildlife-extirpated areas; and (4) assess the effects of P. megacephala invasion on availability of soil and plant nutrients and resulting habitat use by wild herbivores.

在整个自然世界中，人们可以找到一对生活在一起的物种，并为彼此提供服务以促进他们的互惠互利。这些物种相互作用称为互动，被认为可以维持世界上许多生物多样性。互助主义也是重要生态系统服务（例如种子分散，授粉和营养循环）的基础。但是，当一种入侵物种在互助中取代物种伴侣之一时会发生什么？这是该项目将在肯尼亚的Savannas中解决的问题，在肯尼亚的萨纳省，侵入性的蚂蚁物种正在将生活在相思树上的本地蚂蚁取代。本地蚂蚁通过攻击大象和其他吃树木的草食动物来积极地捍卫树木。作为交换，树木为蚂蚁提供食物（含糖的花蜜）和庇护所（荆棘）。相比之下，一个入侵的物种，大头蚂蚁，杀死本地蚂蚁，但不捍卫树木。没有他们的原住民保镖，树木被大象更频繁地被大象杀死。该项目将评估与大头蚂蚁物种侵入相关的树木损失的速度和程度。由于许多野生草食动物，包括濒危黑犀牛，都以一种或另一种方式依靠树木，因此该项目还旨在了解树木流失如何影响野生动植物的栖息地。这项研究提供了一个独特的机会，可以评估具有丰富大象，长颈鹿和其他标志性大型哺乳动物物种的景观中关键物种互助崩溃的多米诺影响。该项目将检验以下假设：侵入性蚂蚁物种P. megacephala对阿拉克人的基础互动和天然蚂蚁之间的基础互动的级联作用是上下文依赖性的。在P. Megacephala入侵的稀树草原中，大象有望减少树木的覆盖，从而降低土壤和植物氮（N），并对野生动植物的饲料和栖息地质量产生负面影响（因为A. drepanolobium是N固定器）。相比之下，在缺乏大象的情况下，大叶氏疟原虫的侵袭应加速树的生长，因为P. megacephala不会诱导花蜜生产，因此可能会降低宿主植物的代谢成本。从长远来看，预计这种司机的崩溃将导致在入侵地区的树木覆盖率和土壤N较高。该项目将（1）在存在和不存在野生草食动物的情况下，尤其是大象的情况下，量化天然与侵入性蚂蚁对树木生长，n固定，繁殖和生物量的影响； （2）使用人口统计学模型来投影树人口增长率； （3）使用遥感来评估野生动植物 - 野生动植物和野生动植物延伸的地区的巨叶氏疟原虫入侵的传播率； （4）评估巨假单胞菌入侵对土壤和植物养分的可用性以及野生草食动物的栖息地的影响。