Data from: Partitioning the relative contribution of one-phase and two-phase seed dispersal when evaluating seed dispersal effectiveness

Seed dispersal effectiveness (SDE) is a conceptual framework that aims at quantifying the contribution of seed dispersal vectors to plant fitness. While it is well recognized that diplochorous dispersal systems, characterized by two successive dispersal steps performed by two different vectors (Phase I = primary seed dispersal and Phase II = secondary seed dispersal) are common in temperate and tropical regions, little attention has been given to distinguishing the relative contribution of one-phase and two-phase dispersal to overall SDE. This conceptual gap probably results from the lack of a clear methodology to include Phase II dispersal into the calculation of SDE and to quantify its relative contribution. We propose a method to evaluate the relative contribution of one-phase and two-phase dispersal to SDE and determine whether two seed dispersers are better than one. To do so, we used the SDE landscape and an extension of the SDE landscape, the Phase II effect landscape, which measures the direction and magnitude of the Phase II dispersal effect on overall SDE. We used simulated and empirical data from a diplochorous dispersal system in the Peruvian Amazon to illustrate this new approach. Our approach provides the relative contribution of one-phase SDE (SDE1) and two-phase SDE (SDE2) to overall SDE and quantifies how much SDE changes with the addition of Phase II dispersal. Considering that the seed dispersal process is context-dependent so that Phase II depends on Phase I, we predict the possible range of variation of SDE according to the variation of the probability of Phase II dispersal. In our specific study system composed of two primate species as primary dispersal vectors and different species of dung beetles as secondary dispersal vectors, the relative contribution of SDE1 and SDE2 to overall SDE varied between plant species. We discuss the context-dependency of the Phase II dispersal and the potential applications of our approach. This extension to the conceptual framework of SDE enables quantitative evaluation of the effect of Phase II dispersal on plant fitness and can be easily adapted to other biotic and/or abiotic diplochorous dispersal systems.

种子扩散有效性（Seed dispersal effectiveness，SDE）是旨在量化种子扩散媒介对植物适合度贡献的概念框架。尽管学界已普遍认可，由两种不同媒介依次完成两次扩散步骤（阶段I=初级种子扩散，阶段II=次级种子扩散）的双阶段扩散系统（diplochorous dispersal systems）在温带与热带地区广泛分布，但针对单阶段与双阶段扩散对整体SDE相对贡献的区分研究却相对匮乏。这一概念缺口大概率源于缺乏将阶段II扩散纳入SDE计算、并量化其相对贡献的清晰方法体系。我们提出了一种评估单阶段与双阶段扩散对SDE相对贡献的方法，可用于判断两种种子扩散者是否优于单一扩散者。为此，我们采用了SDE景观（SDE landscape）及其扩展形式——阶段II效应景观（Phase II effect landscape），该景观可衡量阶段II扩散对整体SDE的作用方向与强度。我们利用秘鲁亚马逊地区双阶段扩散系统的模拟数据与实测数据，对这一新方法进行了实例演示。本方法可分别计算单阶段SDE（SDE1）与双阶段SDE（SDE2）对整体SDE的相对贡献，并量化引入阶段II扩散后SDE的变化幅度。鉴于种子扩散过程具有情境依赖性，且阶段II依赖于阶段I，我们可根据阶段II扩散概率的变化，预测SDE的可能变异范围。在我们以两种灵长类物种作为初级扩散媒介、多种蜣螂作为次级扩散媒介的特定研究系统中，SDE1与SDE2对整体SDE的相对贡献因植物物种不同而存在差异。我们讨论了阶段II扩散的情境依赖性，以及本方法的潜在应用场景。这一对SDE概念框架的扩展，可实现对阶段II扩散对植物适合度影响的量化评估，且可轻松适配其他生物性或非生物性双阶段扩散系统。