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，其中经典范例为孤岛生境（insular habitats）的面积与物种丰富度之间的正相关关系。尽管森林内树冠密度极高且彼此邻近，但对于部分类群而言，树木本身即为孤岛生境。具体而言，冠层羞避（crown shyness）会阻碍小型步行类动物在树木间移动。在此研究中，我们检验了如下假说：嵌入热带林冠中的孤立个体树木，其栖息的蚂蚁物种丰富度（species richness of ants, Sa）会随树木尺寸增大而提升。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烈相互作用以决定树木占据情况时，这一相关模式将会消失。我们对巴拿马低地热带森林中的213个树冠的栖居蚂蚁开展了调查。平均而言，单个树冠栖息有9.2种蚂蚁（范围为2至20种）。有藤本的树木的平均Sa（±标准误）约为10.2 ± 0.26，较无藤本的树木（8.0 ± 0.51）高出约25%。在无藤本的树木中，蚂蚁物种丰富度随树木尺寸增大而提升（Sa = 10.99A^0.256），但在有藤本的树木中未观察到此规律。有藤本与无藤本的树木间，蚂蚁物种组成亦存在显著差异。具体而言，单独觅食的蚂蚁物种在有藤本的树木中出现频率更高。本研究未观测到其他树栖蚂蚁群落中常见的镶嵌状物种共存格局。综合来看，本研究结果表明，藤本植物通过抵消树冠的孤岛生境特性，在塑造树栖蚂蚁的局域群落结构中发挥了关键作用。