Changes in tree community structures in defaunated forests are not driven only by dispersal limitation

1. Bushmeat hunting has reduced population sizes of large frugivorous vertebrates throughout the tropics, thereby reducing the dispersal of seeds. This is believed to affect tree population dynamics, and therefore community composition, because the seed dispersal of large-seeded trees depends upon large-bodied vertebrates. 2. We report on a long-running study of the effect of defaunation on a tropical tree community. In three censuses over 11 years, we compared sapling recruitment between a hunted and a nonhunted site, which are nearby and comparable to one another, to determine the extent to which species composition has changed through time following defaunation. We expected to find a reduced abundance of tree species that rely on large frugivores for dispersal at the hunted site, and altered community structure as a consequence. 3. Although community composition at the hunted site diverged from that at the nonhunted site, the changes were independent of dispersal syndrome, with no trend towards a decline in species that are dispersed by large, hunted vertebrates. Moreover, the loss of large-bodied dispersers did not generate the changes in tree community composition that we hypothesised. Some species presumed to rely on large-bodied frugivores for dispersal are effectively recruiting despite the absence of their dispersers. 4. Synthesis: The presumption that forests depleted of large-bodied dispersers will experience rapid, directional compositional change is not fully supported by our results. Altered species composition in the sapling layer at the hunted site, however, indicates that defaunation may be connected with changes to the tree community, but that the nature of these changes are not unidirectional as previously assumed. It remains difficult to predict how defaunation will affect tree community composition without a deeper understanding of the driving mechanisms at play.

1. 野味狩猎（bushmeat hunting）已造成全球热带区域内大型食果脊椎动物（frugivorous vertebrates）的种群规模缩减，进而削弱了种子传播过程。学界普遍认为该现象会影响树木种群动态乃至群落组成，因为大种子树种的种子传播完全依赖大型脊椎动物。2. 本研究报道了一项针对动物区系丧失（defaunation）对热带树木群落影响的长期定位研究。在11年间开展的3次普查中，我们对比了空间邻近且生境可比的狩猎样地与禁猎样地的幼树更新（sapling recruitment）情况，以明确动物区系丧失后群落组成随时间变化的幅度。我们预期在狩猎样地中，依赖大型食果动物传播种子的树种丰度会降低，并由此引发群落结构改变。3. 尽管狩猎样地的群落组成与禁猎样地出现了分异，但这些变化与扩散综合征（dispersal syndrome）无关，未呈现出依赖被狩猎大型脊椎动物传播的物种种群下降趋势。此外，大型传播者的丧失并未如我们所假设的那样，引发树木群落组成的变化。部分被认为依赖大型食果动物传播种子的物种，即便其传播者缺失，仍能有效完成更新定植。4. 综合分析：认为丧失大型传播者的森林会出现快速定向群落组成变化的预设，并未得到本研究结果的完全支持。但狩猎样地幼树层的物种组成发生改变，这表明动物区系丧失或与树木群落变化存在关联，不过这类变化并非如此前假设的那样呈单向性。若无法更深入理解其背后的驱动机制，我们仍难以预测动物区系丧失将如何影响树木群落组成。