Rapid assessment of the three-dimensional distribution of dominant arboreal ants in tropical forests

Ants are omnipresent in tropical forests, especially territorially dominant arboreal ants whose territories are spatially segregated forming “ant mosaics”. These ecologically important species are rarely used in conservation monitoring because of the difficulty in collecting them. We developed a standardised baitline protocol to study the distribution of dominant ants on canopy trees and also a procedure to objectively define species dominance, even in unknown ant assemblages. Besides eliminating the need to climb trees, this protocol allows live arboreal ant specimens to be sampled at different heights. Behavioural aggressiveness assays between the collected workers provide data on the three-dimensional distribution of colonies and on interactions between species. We compared the results of the behavioural tests to those from null models. In the New Guinean lowland forest studied, we show that the canopy was either shared by multiple territorial species or inhabited by a single species with a large territory. The baitline protocol collected up to half of the arboreal ant species found in a felling census. However, the proportion of species collected at baits decreased with the increasing spatial dominance of single territorial species. Behavioural observations used in the protocol allowed a more efficient detection of ant mosaics than null models. Territorially dominant ants were active on both understorey and canopy trees. The protocol is fast and easy to replicate. It is a potential tool for understanding and monitoring the spatio-temporal dynamics of arboreal ant assemblages and can detect populous colonies, including those of invasive species.

蚂蚁在热带森林中无处不在，尤以具有领地优势的树栖蚂蚁（arboreal ants）最为典型——这类蚂蚁的领地在空间上相互分隔，形成“蚂蚁镶嵌格局”。由于采集难度较高，这类具有重要生态意义的物种极少被应用于保护监测工作中。为此，我们开发了一套标准化诱饵线规程（baitline protocol），用于研究冠层树木上优势蚂蚁的分布情况；同时建立了一套可客观界定物种优势度的流程，即便针对未知的蚂蚁类群亦能适用。该规程无需攀爬树木，即可对不同高度的树栖蚂蚁活体标本进行采样。对采集到的工蚁开展行为攻击性测定，可获取蚁群三维分布以及物种间互作的相关数据。我们将行为测定的结果与零模型（null models）的结果进行了对比分析。在本次研究的新几内亚低地森林中，我们发现冠层要么由多种具有领地性的物种共同占据，要么被单个拥有广阔领地的物种独占。该诱饵线规程可采集到伐木普查中发现的近半数树栖蚂蚁物种，但随着单个领地物种空间优势度的提升，诱饵采样到的物种占比会随之下降。相较于零模型，规程中采用的行为观测可更高效地识别蚂蚁镶嵌格局。具有领地优势的蚂蚁在林下层树木与冠层树木上均有活动。该规程操作快捷且易于重复，可作为理解和监测树栖蚂蚁类群时空动态的潜在工具，还能检测到大型蚁群，包括入侵物种的蚁群。