Hampe Arndt
INRA, UMR 1202 Biodiversity, Genes and Communities (BIOGECO), 69 Route d'Arcachon, 33612 Cestas Cedex, France.
Oecologia. 2008 May;156(1):137-45. doi: 10.1007/s00442-008-0979-0. Epub 2008 Feb 13.
Vertebrate frugivore communities are easily satiated by abundant fruit supplies and, contrary to abiotic dispersal agents, typically disperse only part of the available seed pool. This frugivore satiation is likely to be a widespread phenomenon and should be an influential predictor of plants' ability to disperse their offspring to suitable establishment sites; yet it has never been systematically quantified. Here I investigate patterns of fruit abundance, frugivore activity and frugivore satiation, and their consequences for seed dispersal in the fleshy-fruited tree Frangula alnus. Based on constant-effort seed trapping conducted over 3 years, I assess densities of total and frugivore-consumed seedfall across two spatial (within/between populations) and two temporal (within/between ripening seasons) scales. Furthermore, I examine relationships between fruit abundance and the amount of seeds that are actually dispersed away from fruiting trees. Frugivore activity tightly matched fruit abundance, although some differences existed between scales. This marked fruit tracking did not prevent a significant frugivore satiation, however, and only 53% of the available fruit crops were actually consumed. The extent of satiation varied most at the within-population level, likely due to the territorial behaviour of important frugivore species. In contrast, levels of satiation remained remarkably invariable through time, suggesting that frugivores behave as opportunists and closely adjust the composition of their diet to the available food supply. Overall, greater fruit abundance resulted in a higher proportion of seeds falling beneath fruiting trees, but it also helped increase the (absolute) number of seeds dispersed. This study shows that frugivore satiation can be an important phenomenon even when frugivores tightly track fruit abundance. Its negative effects on recruitment may be attenuated, however, if greater fruit crops help increase population-wide frugivore activity and the amount of seeds being dispersed to suitable establishment sites.
脊椎动物食果动物群落很容易因丰富的果实供应而饱腹，并且与非生物传播媒介不同，它们通常只传播部分可用的种子库。这种食果动物饱腹现象可能是一种普遍存在的现象，应该是植物将其后代传播到合适的定居地点能力的一个有影响力的预测指标；然而，它从未被系统地量化过。在这里，我研究了果实丰度、食果动物活动和食果动物饱腹现象的模式，以及它们对肉质果树桤木种子传播的影响。基于连续3年进行的固定努力种子诱捕，我评估了在两个空间尺度（种群内/种群间）和两个时间尺度（成熟季节内/成熟季节间）上总种子降落量和被食果动物消耗的种子降落量的密度。此外，我还研究了果实丰度与实际从结果树上传播出去的种子数量之间的关系。食果动物的活动与果实丰度紧密匹配，尽管不同尺度之间存在一些差异。然而，这种明显的果实追踪并没有阻止显著的食果动物饱腹现象，实际上只有53%的可用果实作物被消耗。饱腹程度在种群内水平上变化最大，这可能是由于重要食果动物物种的领地行为。相比之下，饱腹程度随时间保持相当稳定，这表明食果动物表现为机会主义者，并根据可用食物供应密切调整其饮食组成。总体而言，果实丰度越高，落在结果树下的种子比例就越高，但它也有助于增加（绝对）传播的种子数量。这项研究表明，即使食果动物紧密追踪果实丰度，食果动物饱腹现象也可能是一个重要现象。然而，如果更多的果实作物有助于增加全种群的食果动物活动以及传播到合适定居地点的种子数量，那么它对补充更新的负面影响可能会减弱。
