Kirstenbosch Research Centre, South African National Biodiversity Institute, Newlands, 7735 Cape Town, South Africa;
Statistics in Ecology, Environment and Conservation, Department of Statistical Sciences, University of Cape Town, 7701 Rondebosch, South Africa.
Proc Natl Acad Sci U S A. 2020 Aug 18;117(33):20027-20037. doi: 10.1073/pnas.1915646117. Epub 2020 Aug 5.
Research on global patterns of diversity has been dominated by studies seeking explanations for the equator-to-poles decline in richness of most groups of organisms, namely the latitudinal diversity gradient. A problem with this gradient is that it conflates two key explanations, namely biome stability (age and area) and productivity (ecological opportunity). Investigating longitudinal gradients in diversity can overcome this problem. Here we investigate a longitudinal gradient in plant diversity in the megadiverse Cape Floristic Region (CFR). We test predictions of the age and area and ecological opportunity hypotheses using metrics for both taxonomic and phylogenetic diversity and turnover. Our plant dataset includes modeled occurrences for 4,813 species and dated molecular phylogenies for 21 clades endemic to the CFR. Climate and biome stability were quantified over the past 140,000 y for testing the age and area hypothesis, and measures of topographic diversity, rainfall seasonality, and productivity were used to test the ecological opportunity hypothesis. Results from our spatial regression models showed biome stability, rainfall seasonality, and topographic heterogeneity were the strongest predictors of taxonomic diversity. Biome stability alone was the strongest predictor of all diversity metrics, and productivity played only a marginal role. We argue that age and area in conjunction with non-productivity-based measures of ecological opportunity explain the CFR's longitudinal diversity gradient. We suggest that this model may possibly be a general explanation for global diversity patterns, unconstrained as it is by the collinearities underpinning the latitudinal diversity gradient.
全球多样性模式的研究一直以来主要集中于寻求解释大多数生物类群（即纬度多样性梯度）从赤道到两极丰富度下降的原因。该梯度存在一个问题，即它混淆了两个关键的解释，即生物群落稳定性（年龄和面积）和生产力（生态机会）。研究多样性的经度梯度可以解决这个问题。在这里，我们研究了生物多样性丰富的开普植物区系（Cape Floristic Region，CFR）的植物多样性的经度梯度。我们使用分类和系统发育多样性以及周转率的指标来检验年龄和面积以及生态机会假说的预测。我们的植物数据集包括 4813 个物种的模型出现以及 CFR 特有 21 个分支的分子系统发育。气候和生物群落稳定性在过去 14 万年中进行了量化，以检验年龄和面积假说，地形多样性、降雨季节性和生产力的度量用于检验生态机会假说。我们的空间回归模型的结果表明，生物群落稳定性、降雨季节性和地形异质性是分类多样性的最强预测因子。生物群落稳定性是所有多样性指标的最强预测因子，而生产力仅起次要作用。我们认为，年龄和面积加上非基于生产力的生态机会措施可以解释 CFR 的经度多样性梯度。我们认为，该模型可能是全球多样性模式的一种普遍解释，不受纬度多样性梯度基础的共线性的限制。
