Department of Ecology and Animal Biology, University of Vigo, EUET Forestal, Campus Universitario, E36005 Pontevedra, Spain.
Ecology. 2009 Dec;90(12):3503-15. doi: 10.1890/08-1629.1.
Disperser effectiveness is the number of new plants resulting from the activity of one disperser relative to other dispersers or to nondispersed seeds. Effectiveness remains largely uninvestigated due to the complexity of its measurement. We measured the effectiveness of seed dispersers (Larus michahellis, Turdus merula, and Oryctolagus cuniculus) of the shrub Corema album (Empetraceae) using a simulation model of the recruitment process that was parameterized with field data of seed dispersal, predation, and seedling emergence and validated with independent data on seedling density. The model allows tracking the fate of seeds dispersed by each animal and estimating, for the first time, disperser effectiveness as seedlings per square meter contributed by each disperser. It also allows quantifying the relative importance of different recruitment processes in determining the quantity and spatial distribution of recruitment. Larus michahellis was the most effective disperser in two of the three habitats studied, contributing 3-125 times more than the other two species, whose lower effectiveness depended mostly on deposition patterns (T. merula) or deleterious effects on seedling emergence (O. cuniculus). The dependence of the plant on each disperser differed between habitats and was the greatest in sparse scrub, where recruitment depended almost exclusively on gulls (90%). Quantity and quality of dispersal were not correlated; quality was a better predictor of disperser effectiveness. Seedling emergence was the most crucial process in determining both the spatial pattern of recruitment among microhabitats (99.8% of variance explained) and the quantity of recruitment within microhabitats (43-83%). A sensitivity analysis showed that increasing seed dispersal improved the recruitment for all dispersers when there was no competition for fruits. However, with limited fruits, increased dispersal of lower quality dispersers reduced overall recruitment. Our results show important differences in effectiveness among dispersers and illustrate the different influences of the components of effectiveness, which varied depending not only on the disperser but also on the circumstances (e.g., type of habitat).
传播者效能是指一个传播者相对于其他传播者或未分散的种子，产生的新植物的数量。由于其测量的复杂性，传播者效能在很大程度上仍未得到研究。我们使用基于野外数据的种子传播、捕食和幼苗出现的模拟模型，测量了灌木 Corema album（岩高兰科）的种子传播者（海鸥、红腹灰雀和欧洲兔）的效能，并使用独立的幼苗密度数据对模型进行了验证。该模型允许跟踪每个动物传播的种子的命运，并首次估计每个传播者每平方米贡献的幼苗数量，以此作为传播者效能。它还允许量化不同的招募过程在确定招募的数量和空间分布方面的相对重要性。在研究的三个栖息地中的两个中，海鸥是最有效的传播者，其效能比其他两种动物高出 3-125 倍，后两者的低效能主要取决于沉积模式（红腹灰雀）或对幼苗出现的有害影响（欧洲兔）。植物对每个传播者的依赖程度在不同的栖息地之间有所不同，在稀疏的灌木丛中最大，在那里，几乎完全依赖海鸥进行招募（90%）。数量和质量的传播没有相关性；质量是传播者效能的更好预测指标。幼苗出现是决定微生境之间的招募空间模式（解释方差的 99.8%）和微生境内的招募数量（43-83%）的最关键过程。敏感性分析表明，在没有果实竞争的情况下，增加种子传播可以提高所有传播者的招募效果。然而，在果实有限的情况下，低质量传播者的传播增加会降低整体招募效果。我们的研究结果表明传播者之间存在重要的效能差异，并说明了效能的不同影响因素，这些因素不仅取决于传播者，还取决于环境（例如，栖息地类型）。
