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；一个经典案例是岛屿生境面积与物种丰富度之间的正相关关系。尽管森林中树冠密度高且彼此邻近，但树木对于某些类群而言仍是岛屿状生境。具体而言，树冠隔离（即树冠回避，crown shyness）会阻碍小型步行动物在树木间的移动。本研究旨在检验以下假说：嵌入热带林冠中的孤立单株树木，其栖息的蚂蚁物种丰富度（Sa）会随树木大小增大而升高。我们预测，当树木被藤本植物（木质藤本）连接，或是蚂蚁物种间存在强相互作用决定其树木占据情况时，这一模式会消失。我们对巴拿马低地热带雨林中的213个树冠的定居蚂蚁进行了调查。单株树冠平均栖息9.2（范围2~20）个蚂蚁物种。有藤本连接的树木的平均（±标准误）Sa约为10.2±0.26，较无藤本树木的8.0±0.51高出约25%。在无藤本的树木中，Sa随树木大小增大而升高（Sa = 10.99×A^0.256），但在有藤本连接的树木中则无此规律。有藤本与无藤本树木的蚂蚁物种组成也存在差异。具体而言，单独觅食的蚂蚁物种在有藤本连接的树木中出现频率更高。此前在其他树栖蚂蚁群落中观察到的斑块状物种共存格局，在本研究的森林中并未发现。综上，本研究结果表明，藤本植物通过抵消树冠的岛屿化属性，在塑造树栖蚂蚁的局域群落结构中发挥了重要作用。