Divaricate plant species account for more than 10% of New Zealand/Aotearoa's woody flora, a higher proportion for that life form than anywhere else on earth. Two main hypotheses have been proposed to account for the prevalence of this phenotype. The first suggests herbivorous birds, particularly large flightless moa, exerted selective pressure on many plants to adopt the form. The second proposes climate as the main driver since insular New Zealand has many exposed habitats and, historically, experienced stressing conditions during the Pleistocene. Our study investigated two questions to shed further light on the evolution of divaricates, in particular related to the potential influence of browsing by large avian herbivores. First, divaricate plants have been posited to have a higher tensile strength than non-divaricates as a defence mechanism against moa browsing. We tested the great majority of New Zealand plant genera within which divaricates occur, contrasting the stem tensile strength of these plants against their closest non-divaricate counterparts using accurate testing technology. The results indicate divaricate species have tensile strength that approaches twice that of non-divaricates across a broad and disparate phylogenetic range that includes gymnosperms and many clades of angiosperms. Second, we tested the species level distributions of widely dispersed woody plant genera across the New Zealand archipelago on islands where moa had been present or always absent. We found that no endemic divaricate species occurred on any islands from which moa had been permanently absent. In contrast, their non-divaricate counterparts were commonly endemic to those same islands.

中文翻译：

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新西兰分支植物物种：抗拉强度和偏远岛屿发生

异种植物物种占新西兰/奥特阿罗阿木本植物群的 10% 以上，该生命形式的比例高于地球上任何其他地方。已经提出了两个主要假设来解释这种表型的流行。第一个建议表明食草鸟类，特别是大型不会飞的恐鸟，对许多植物施加选择压力以采用这种形式。第二个建议将气候作为主要驱动因素，因为新西兰岛屿有许多暴露的栖息地，并且从历史上看，在更新世期间经历了压力条件。我们的研究调查了两个问题，以进一步阐明分支的进化，特别是与大型鸟类食草动物浏览的潜在影响有关。第一的，已经假定，作为抵御恐鸟啃食的防御机制，分支植物比非分支植物具有更高的抗拉强度。我们测试了大多数新西兰植物属，其中出现了分支，使用精确的测试技术将这些植物的茎抗拉强度与其最接近的非分支对应物进行对比。结果表明，在包括裸子植物和许多被子植物进化枝在内的广泛而不同的系统发育范围内，异种植物的抗拉强度接近非异种植物的两倍。其次，我们测试了新西兰群岛上广泛分布的木本植物属的物种水平分布，这些植物属在恐鸟存在或始终不存在的岛屿上。我们发现，在恐鸟永久消失的任何岛屿上都没有出现地方性的分支物种。相比之下，它们的非差异对应物通常是这些岛屿的特有种。