Skaien Cora L, Arcese Peter
Department of Forest and Conservation Sciences, Faculty of Forestry, University of British Columbia, 2424 Main Mall, Vancouver, British Columbia, V6T 1Z4, Canada.
Ecology. 2020 Jul;101(7):e03054. doi: 10.1002/ecy.3054. Epub 2020 May 8.
Spatial variation in the occurrence of browsing ungulates can drive local adaptation in plant traits but also lead to trade-offs among traits potentially enhancing competitive ability versus resistance or tolerance to browsing. Plectritis congesta populations co-occurring on islands with and without ungulates offer striking examples of population-level variation in traits, such as plant height and fruit morphology, which may also affect fitness. We monitored split-plot common gardens exposed to and protected from browsing ungulates for 5 yr to test for local adaptation (local vs. foreign comparison) in P. congesta by comparing the survival and fecundity of 4,392 sown fruits from six island populations where ungulates were present ("historically exposed") and six where they were absent ("historically naïve"). Our results indicate that local adaptation to browsing in P. congesta favored rosette formation, delayed flowering, reduced height, and the production of wingless fruits, all of which appeared to enhance survival, fecundity, and population growth in plants from populations historically exposed to ungulate browsers, as compared to plants from historically naïve populations. In contrast, plants from historically naïve populations displayed higher relative fitness in the absence of ungulates, increased in height, flowered earlier, and produced fewer but larger, winged fruits, often in large terminal inflorescences. Our results support the hypothesis that variation in the occurrence of ungulate browsers has led to (1) spatial heterogeneity in natural selection and rapid adaptation in P. congesta populations on islands, and (2) context-dependent trade-offs in the fitness value of traits linked to the resistance or tolerance of browsing versus success in competition for light, pollinators, or other resources. Because patterns of selection in plant communities will vary with the introduction or extirpation of top predators or browsers, we suggest historical context, local adaptation, and the capacity for rapid adaptation should be a focal concern of those aiming to maximize or predict population persistence under environmental change in conservation plans.
有蹄食草动物出现的空间差异能够驱动植物性状的局部适应性，但也会导致性状之间的权衡，这些权衡可能会增强植物的竞争能力，同时也影响其对啃食的抗性或耐受性。在有蹄类动物存在和不存在的岛屿上共同出现的丛生福禄考种群，提供了性状在种群水平上变异的显著例子，如株高和果实形态，这些性状也可能影响适合度。我们对暴露于有蹄食草动物啃食和受到保护不被啃食的裂区共同花园进行了5年的监测，通过比较来自六个有有蹄类动物存在的岛屿种群（“历史上暴露的”）和六个没有有蹄类动物的岛屿种群（“历史上未接触过的”）的4392颗播种果实的存活率和繁殖力，来测试丛生福禄考的局部适应性（本地与外来比较）。我们的结果表明，丛生福禄考对啃食的局部适应性有利于莲座丛形成、开花延迟、高度降低以及无翅果实的产生，与来自历史上未接触过有蹄类动物啃食的种群的植物相比，所有这些似乎都提高了历史上暴露于有蹄类动物啃食的种群中植物的存活率、繁殖力和种群增长。相比之下，来自历史上未接触过有蹄类动物啃食的种群的植物在没有有蹄类动物的情况下表现出更高的相对适合度，植株更高，开花更早，产生的果实数量更少但更大且有翅，通常在大型顶生花序中。我们的结果支持了这样的假设，即有蹄类动物啃食出现情况的差异导致了：（1）自然选择中的空间异质性以及岛屿上丛生福禄考种群的快速适应性，（2）与对啃食的抗性或耐受性相关的性状适合度值与在争夺光照、传粉者或其他资源的竞争中的成功之间的背景依赖性权衡。由于植物群落中的选择模式会随着顶级捕食者或食草动物的引入或灭绝而变化，我们建议，历史背景、局部适应性以及快速适应能力应该成为那些旨在保护计划中在环境变化下最大化或预测种群持久性的人们关注的焦点。
