Data from: Trees as islands: canopy ant species richness increases with the size of liana-free trees in a Neotropical forest

The physical characteristics of habitats shape local community structure; a classic example is the positive relationship between the size of insular habitats and species richness. Despite the high density and proximity of tree crowns in forests, trees are insular habitats for some taxa. Specifically, crown isolation (i.e. crown shyness) prevents the movement of small cursorial animals among trees. Here, we tested the hypothesis that the species richness of ants (Sa) in individual, isolated trees embedded within tropical forest canopies increases with tree size. We predicted that this pattern disappears when trees are connected by lianas (woody vines) or when strong interactions among ant species determine tree occupancy. We surveyed the resident ants of 213 tree crowns in lowland tropical forest of Panama. On average, 9.2 (range = 2–20) ant species occupied a single tree crown. Average (± SE) Sa was ca 25% higher in trees with lianas (10.2 ± 0.26) than trees lacking lianas (8.0 ± 0.51). Sa increased with tree size in liana-free trees (Sa = 10.99A0.256), but not in trees with lianas. Ant species composition also differed between trees with and without lianas. Specifically, ant species with solitary foragers occurred more frequently in trees with lianas. The mosaic-like pattern of species co-occurrence observed in other arboreal ant communities was not found in this forest. Collectively, the results of this study indicate that lianas play an important role in shaping the local community structure of arboreal ants by overcoming the insular nature of tree crowns.

生境的物理特征塑造局域群落结构，其中经典范例之一便是岛屿状生境的面积与物种丰富度间的正相关关系。尽管森林内树冠密度极高且彼此邻接，但对部分分类群而言，单棵树木本身即为独立的岛屿状生境。具体而言，冠层隔离（即冠层羞避，crown shyness）会阻碍小型奔走型动物在树木间的移动。本研究旨在验证如下假说：嵌入热带林冠中的孤立单棵树木内的蚂蚁物种丰富度（Species Richness of Ants，下称Sa）随树木体量增大而提升。我们预测，当树木通过藤本（木质藤本）相互连接，或是蚂蚁物种间的强相互作用决定了蚂蚁对树木的占据情况时，这一规律将不复存在。我们对巴拿马低地热带森林中的213个树冠层的栖息蚂蚁开展了调查。单棵树冠平均栖息9.2种蚂蚁（区间为2至20种）。带有藤本的树木的Sa平均值（±标准误，Standard Error）较无藤本树木高出约25%，分别为10.2±0.26与8.0±0.51。在无藤本的树木中，Sa随树木体量增大呈幂函数增长（Sa = 10.99A^0.256），但在带有藤本的树木中未观测到此规律。有藤本与无藤本树木的蚂蚁物种组成亦存在显著差异。具体而言，偏好单独觅食的蚂蚁物种在带有藤本的树木中出现频率更高。其他树栖蚂蚁群落中常见的斑块状物种共存模式，在本研究的森林中并未被发现。综合来看，本研究结果表明，藤本通过消解树冠的岛屿状生境特性，在塑造树栖蚂蚁的局域群落结构中发挥了关键作用。