Department of Ecology, Evolution and Environmental Biology, Columbia University, 1200 Amsterdam Ave., New York, New York 10027, USA.
Ecology. 2011 Apr;92(4):924-37. doi: 10.1890/10-0709.1.
Seed dispersal is a crucial component of plant population dynamics. Human landscape modifications, such as habitat destruction and fragmentation, can alter the abundance of fruiting plants and animal dispersers, foraging rates, vector movement, and the composition of the disperser community, all of which can singly or in concert affect seed dispersal. Here, we quantify and tease apart the effects of landscape configuration, namely, fragmentation of primary forest and the composition of the surrounding forest matrix, on individual components of seed dispersal of Heliconia acuminata, an Amazonian understory herb. First we identified the effects of landscape configuration on the abundance of fruiting plants and six bird disperser species. Although highly variable in space and time, densities of fruiting plants were similar in continuous forest and fragments. However, the two largest-bodied avian dispersers were less common or absent in small fragments. Second, we determined whether fragmentation affected foraging rates. Fruit removal rates were similar and very high across the landscape, suggesting that Heliconia fruits are a key resource for small frugivores in this landscape. Third, we used radiotelemetry and statistical models to quantify how landscape configuration influences vector movement patterns. Bird dispersers flew farther and faster, and perched longer in primary relative to secondary forests. One species also altered its movement direction in response to habitat boundaries between primary and secondary forests. Finally, we parameterized a simulation model linking data on fruit density and disperser abundance and behavior with empirical estimates of seed retention times to generate seed dispersal patterns in two hypothetical landscapes. Despite clear changes in bird movement in response to landscape configuration, our simulations demonstrate that these differences had negligible effects on dispersal distances. However, small fragments had reduced densities of Turdus albicollis, the largest-bodied disperser and the only one to both regurgitate and defecate seeds. This change in Turdus abundance acted together with lower numbers of fruiting plants in small fragments to decrease the probability of long-distance dispersal events from small patches. These findings emphasize the importance of foraging style for seed dispersal and highlight the primacy of habitat size relative to spatial configuration in preserving biotic interactions.
种子传播是植物种群动态的关键组成部分。人类对景观的改造，如栖息地的破坏和破碎化，会改变结果实植物和动物传播者的丰度、觅食率、媒介物的移动以及传播者群落的组成，所有这些因素都可能单独或协同影响种子传播。在这里，我们量化并剖析了景观配置（即原始森林的破碎化和周围森林基质的组成）对亚马逊林下草本植物 Heliconia acuminata 种子传播的各个组成部分的影响。首先，我们确定了景观配置对结果实植物和六种鸟类传播者数量的影响。尽管结果实植物的密度在空间和时间上变化很大，但在连续森林和片段中的密度相似。然而，两种体型最大的鸟类传播者在小片段中较少见或不存在。其次，我们确定了破碎化是否影响觅食率。在整个景观中，果实去除率相似且非常高，这表明 Heliconia 果实是该景观中小食果动物的关键资源。第三，我们使用无线电遥测和统计模型来量化景观配置如何影响媒介物的移动模式。鸟类传播者在原始森林中飞行得更远、更快，停留的时间也更长。一种物种还改变了其在原始森林和次生林之间的栖息地边界处的运动方向。最后，我们根据果实密度和传播者丰度和行为的数据，结合对种子保留时间的经验估计，对两个假设的景观进行了模拟模型参数化，以生成种子传播模式。尽管鸟类运动对景观配置有明显的变化，但我们的模拟表明，这些差异对传播距离的影响可以忽略不计。然而，在小片段中，体型最大的传播者 Turdus albicollis 的密度降低了，而且只有它会反刍和排泄种子。这种 Turdus 丰度的变化与小片段中结果实植物数量的减少一起，降低了小斑块中长距离扩散事件的可能性。这些发现强调了觅食方式对种子传播的重要性，并突出了栖息地大小相对于空间配置在保护生物相互作用方面的首要地位。
