Bio21 Institute, School of Biosciences, The University of Melbourne, Parkville, Victoria, 3010, Australia.
The Royal Botanic Gardens of Victoria, Melbourne, Victoria, 3141, Australia.
Ecology. 2017 Oct;98(10):2708-2724. doi: 10.1002/ecy.1964. Epub 2017 Aug 22.
Relatively common species within a clade are expected to perform well across a wider range of conditions than their rarer relatives, yet experimental tests of this "niche-breadth-range-size" hypothesis remain surprisingly scarce. Rarity may arise due to trade-offs between specialization and performance across a wide range of environments. Here we use common garden and reciprocal transplant experiments to test the niche-breadth-range-size hypothesis, focusing on four common and three rare endemic alpine daisies (Brachyscome spp.) from the Australian Alps. We used three experimental contexts: (1) alpine reciprocal seedling experiment, a test of seedling survival and growth in three alpine habitat types differing in environmental quality and species diversity; (2) warm environment common garden, a test of whether common daisy species have higher growth rates and phenotypic plasticity, assessed in a common garden in a warmer climate and run simultaneously with experiment 1; and (3) alpine reciprocal seed experiment, a test of seed germination capacity and viability in the same three alpine habitat types as in experiment 1. In the alpine reciprocal seedling experiment, survival of all species was highest in the open heathland habitat where overall plant diversity is high, suggesting a general, positive response to a relatively productive, low-stress environment. We found only partial support for higher survival of rare species in their habitats of origin. In the warm environment common garden, three common daisies exhibited greater growth and biomass than two rare species, but the other rare species performed as well as the common species. In the alpine reciprocal seed experiment, common daisies exhibited higher germination across most habitats, but rare species maintained a higher proportion of viable seed in all conditions, suggesting different life history strategies. These results indicate that some but not all rare, alpine endemics exhibit stress tolerance at the cost of reduced growth rates in low-stress environments compared to common species. Finally, these findings suggest the seed stage is important in the persistence of rare species, and they provide only weak support at the seedling stage for the niche-breadth-range-size hypothesis.
在一个进化枝内，相对常见的物种预计会在更广泛的条件下表现良好，而它们较为罕见的亲缘种则不然。然而，对这一“生态位广度-体型大小”假说的实验检验仍然非常罕见。稀有性可能是由于在广泛的环境中专业化和表现之间的权衡造成的。在这里，我们使用共同花园和相互移植实验来检验生态位广度-体型大小假说，重点关注澳大利亚阿尔卑斯山的四种常见和三种罕见的特有高山雏菊（Brachyscome spp.）。我们使用了三种实验环境：（1）高山相互幼苗实验，检验幼苗在三种不同环境质量和物种多样性的高山生境类型中的生存和生长情况；（2）温暖环境共同花园，检验常见雏菊物种是否具有更高的生长速度和表型可塑性，在一个温暖气候的共同花园中进行评估，并与实验 1 同时进行；（3）高山相互种子实验，检验在与实验 1 相同的三种高山生境类型中的种子萌发能力和活力。在高山相互幼苗实验中，所有物种在开阔的石南荒地生境中的存活率最高，而该生境的植物多样性较高，这表明它们对相对多产、低压力的环境有普遍的积极反应。我们只发现了少数稀有物种在其起源栖息地中存活率更高的支持证据。在温暖环境的共同花园中，三种常见的雏菊表现出比两种罕见物种更高的生长和生物量，但另一种罕见物种的表现与常见物种一样好。在高山相互种子实验中，常见雏菊在大多数生境中表现出更高的萌发率，但在所有条件下，罕见物种都保持了更高比例的有活力的种子，这表明它们采用了不同的生活史策略。这些结果表明，一些但不是所有的稀有、高山特有种在低压力环境中表现出对压力的耐受性，但其生长速度会降低，与常见物种相比。最后，这些发现表明种子阶段对稀有物种的生存很重要，并且在幼苗阶段仅对生态位广度-体型大小假说提供了微弱的支持。
