Ricklefs Robert E
Department of Biology, University of Missouri-St. Louis, 8001 Natural Bridge Road, St. Louis, Missouri 63121-4499, USA.
Ecology. 2006 Oct;87(10):2468-78. doi: 10.1890/0012-9658(2006)87[2468:gvitdr]2.0.co;2.
Net diversification rates were estimated for samples of primarily tribe-to-family-level clades of passerine birds, taking into account extinction as well as speciation. Two samples were used. The first consisted of 37 clades of primarily temperate North American and primarily tropical South American passerines; the second comprised a global set of 90 clades, each distributed within one or more zoogeographic regions. Circumscription and ages of clades were taken from Sibley and Ahlquist's phylogeny based on DNA hybridization, with updates from more recent sequence analysis. Under a homogeneous speciation (rate = lamda) and extinction (rate = mu) process, the expected number of species (N) after t units of time can be described by the expression, N(t)= [exp(lamda(1 - kappa) t - kappa]/(1 - kappa), where kappa = mu/lamda. A nonlinear least-squares regression for the temperate and tropical American clades with more than one species estimated kappa = 0.938 +/- 0.076 (mean +/- SE), suggesting a high rate of turnover of lineages within clades. Because of the broad confidence limits in kappa, I used values ranging from 0.80 to 0.98 to calculate speciation rates in subsequent analyses, assuming that kappa is uniform among clades and does not vary with latitude. Speciation rate among South American clades exceeded that among North American clades for all kappa, whether monophyletic lineages were included or not. The estimated speciation rate was negatively related to clade age, suggesting that proliferation within clades slows with time. In the global data set, rate of speciation decreased with clade age and increased with the area of the region or regions within which a clade is distributed, and for any given value of kappa the speciation rate was significantly higher in tropical than in temperate regions. Relaxing the assumption of latitude independence in kappa, larger clade size in the tropics could be achieved by various combinations of relative speciation and extinction rates that obscure the underlying causes of global biodiversity patterns. Nonetheless, the results of this analysis clearly indicate that a higher rate of diversification in the tropics contributes to the pervasive latitudinal gradient in diversity observed in passerine birds.
在考虑灭绝和物种形成的情况下，对雀形目鸟类主要从族到科水平的分支样本进行了净多样化率估计。使用了两个样本。第一个样本由37个主要为温带北美和主要为热带南美雀形目的分支组成；第二个样本包括一组全球范围的90个分支，每个分支分布在一个或多个动物地理区域内。分支的界定和年龄取自基于DNA杂交的西布利和阿尔奎斯特系统发育树，并结合了最新序列分析的更新内容。在均匀物种形成（速率=λ）和灭绝（速率=μ）过程下，经过t个时间单位后的预期物种数量（N）可以用表达式N(t)= [exp(λ(1 - κ) t - κ)]/(1 - κ)来描述，其中κ = μ/λ。对有多个物种的温带和热带美洲分支进行非线性最小二乘回归，估计κ = 0.938 ± 0.076（均值±标准误），这表明分支内谱系的更替率很高。由于κ的置信区间较宽，在后续分析中，我使用0.80至0.98的值来计算物种形成率，假设κ在各分支中是一致的且不随纬度变化。无论是否包括单系谱系，对于所有κ值，南美分支的物种形成率都超过北美分支。估计的物种形成率与分支年龄呈负相关，这表明分支内的增殖随时间减缓。在全球数据集中，物种形成率随分支年龄下降，随分支分布的一个或多个区域的面积增加，并且对于任何给定的κ值，热带地区的物种形成率显著高于温带地区。放宽κ与纬度无关的假设，热带地区较大的分支规模可以通过相对物种形成率和灭绝率的各种组合来实现，这掩盖了全球生物多样性模式的潜在原因。尽管如此，该分析结果清楚地表明，热带地区较高的多样化率促成了雀形目鸟类中普遍存在的多样性纬度梯度。
