Edwards Will, Moles Angela T, Chong Caroline
College of Marine and Environmental Sciences, James Cook University, Cairns, Australia; Centre for Tropical Biodiversity and Climate Change, James Cook University, Cairns, Australia.
Evolution & Ecology Research Centre, School of Biological, Earth and Environmental Sciences, UNSW, Sydney, Australia.
PLoS One. 2015 Apr 1;10(4):e0121724. doi: 10.1371/journal.pone.0121724. eCollection 2015.
Among co-occurring species, values for functionally important plant traits span orders of magnitude, are uni-modal, and generally positively skewed. Such data are usually log-transformed "for normality" but no convincing mechanistic explanation for a log-normal expectation exists. Here we propose a hypothesis for the distribution of seed masses based on generalised extreme value distributions (GEVs), a class of probability distributions used in climatology to characterise the impact of event magnitudes and frequencies; events that impose strong directional selection on biological traits. In tests involving datasets from 34 locations across the globe, GEVs described log10 seed mass distributions as well or better than conventional normalising statistics in 79% of cases, and revealed a systematic tendency for an overabundance of small seed sizes associated with low latitudes. GEVs characterise disturbance events experienced in a location to which individual species' life histories could respond, providing a natural, biological explanation for trait expression that is lacking from all previous hypotheses attempting to describe trait distributions in multispecies assemblages. We suggest that GEVs could provide a mechanistic explanation for plant trait distributions and potentially link biology and climatology under a single paradigm.
在同时出现的物种中，功能重要的植物性状值跨越多个数量级，呈单峰分布，且通常为正偏态。此类数据通常会进行对数转换以“使其呈正态分布”，但对于对数正态期望不存在令人信服的机理解释。在此，我们基于广义极值分布（GEV）提出一个关于种子质量分布的假说，广义极值分布是气候学中用于描述事件大小和频率影响的一类概率分布；这些事件对生物性状施加强烈的定向选择。在涉及全球34个地点数据集的测试中，在79%的情况下，广义极值分布对log10种子质量分布的描述与传统归一化统计方法一样好或更好，并且揭示了与低纬度地区相关的小种子大小过度丰富的系统趋势。广义极值分布表征了一个地点经历的干扰事件，单个物种的生活史可能对此做出反应，为性状表达提供了一种自然的生物学解释，而这是以往所有试图描述多物种组合中性状分布的假说所缺乏的。我们认为，广义极值分布可以为植物性状分布提供机理解释，并有可能在单一范式下将生物学和气候学联系起来。
