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.

蚂蚁广泛分布于热带森林中，其中领地优势型树栖蚂蚁（territorially dominant arboreal ants）尤为常见。这类蚂蚁的领地呈空间分隔状态，进而形成蚂蚁镶嵌格局（ant mosaics）。这类具有重要生态价值的类群因采集难度较高，极少被应用于保护监测工作中。本研究开发了一套标准化诱饵线采样规程（standardised baitline protocol），用于探究冠层树木上优势蚂蚁的分布特征；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组合亦能适用。

该规程无需攀爬树木，即可采集不同高度的活体树栖蚂蚁标本。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及物种间互作的相关数据。本研究将行为测试结果与零模型（null models）的模拟结果进行了对比。

在所研究的新几内亚低地森林中，冠层要么由多种领地型物种共同占据，要么被单一拥有大面积领地的物种独占。该诱饵线采样规程可采集到伐倒木普查（felling census）中发现的半数树栖蚂蚁物种，但随着单一领地型物种空间优势度的提升，诱饵线上采集到的物种占比会逐渐降低。

相较于零模型，本规程所采用的行为观测方法可更高效地识别蚂蚁镶嵌格局。领地优势型蚂蚁在下层树木（understorey trees）与冠层树木上均有活动。

该采样规程操作简便、易于复现，可作为探究和监测树栖蚂蚁类群组合时空动态的潜在工具，同时还能检测到种群庞大的蚁群，包括入侵物种（invasive species）的蚁群。