Active modification of cavity nest-entrances is a common strategy in arboreal ants

The majority of tropical arboreal ant species nest in tree cavities. These cavities, often produced initially by wood-boring beetles, can be in live or dead wood and represent long-lasting and highly defensible nesting resources. Yet the size of cavity entrances can constrain their use. Active entrance modification may be an effective way to overcome this constraint. Here, we conduct the first systematic study of nest-entrance modification in an arboreal ant community. Using field experiments deployed across a number of tree species, we show that 14% of 2631 experimental cavities were modified by either enlargement, or reducing entrance size by construction. Entrance modifications, which were made by a majority (18/29 species) of the species that occupied experimental nests, used a variety of construction techniques and materials. Combined, these modifications were context-dependent with respect to available entrance sizes: enlargement was more common when the diversity of available entrance sizes was limited, whereas reduction was more prevalent when the diversity of entrance sizes was higher. Nevertheless, the context of tree species identity did not significantly influence the number of modified cavities or the construction materials. Overall, we show that nest-entrance modification is a widespread, active, and context-dependent strategy in the nesting ecology of arboreal ants.

绝大多数热带树栖蚂蚁（arboreal ant）会在树洞（tree cavities）中筑巢。这些树洞最初多由蛀木甲虫（wood-boring beetles）钻蛀形成，可存在于活木或枯木之中，属于一类持久且极具防御优势的筑巢资源。然而树洞入口的尺寸会限制蚂蚁对其的利用。主动改造巢穴入口或许是突破这一限制的有效策略。本研究首次针对树栖蚂蚁群落的巢穴入口改造行为开展系统性研究。依托多树种布设的野外实验，我们发现2631个实验树洞中，有14%被蚂蚁通过扩大入口尺寸或通过构筑行为缩小入口尺寸的方式完成改造。在占据实验树洞的29个蚂蚁物种中，有18个物种会实施入口改造行为，它们采用了多样的构筑技术与材料。整体而言，此类改造行为会根据可获取的入口尺寸范围呈现情境依赖性：当可选择的入口尺寸多样性较低时，扩大入口的改造更为常见；而当入口尺寸多样性更高时，缩小入口的改造则更为普遍。不过，宿主树种的种类并未对改造树洞的数量或所使用的构筑材料产生显著影响。综上，本研究证实，巢穴入口改造是树栖蚂蚁筑巢生态学中一种广泛存在、主动且具有情境依赖性的生存策略。