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）物种会在树洞（tree cavity）中筑巢。这类树洞最初多由蛀木甲虫（wood-boring beetle）开凿形成，可存在于活木或枯木之中，是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，主动对巢穴入口进行改造或许是克服这一限制的有效途径。 本研究首次对树栖蚂蚁群落的巢穴入口改造（nest-entrance modification）行为开展系统性研究。通过在多种树木上布设野外实验，我们发现2631个实验树洞中有14%被蚂蚁通过扩大入口或搭建结构缩小入口尺寸的方式进行了改造。参与改造的物种涵盖了占据实验巢穴的大部分类群（29种中的18种），它们采用了多样的施工技术与筑造材料。 整体而言，这类改造行为对可用入口尺寸的多样性具有环境依赖性：当可用入口尺寸多样性较低时，扩大入口的改造行为更为常见；而当入口尺寸多样性较高时，缩小入口的改造则更为普遍。不过，寄主树木的种类并未对改造树洞的数量或筑造材料产生显著影响。 综上，本研究表明，巢穴入口改造行为在树栖蚂蚁的筑巢生态学中是一种广泛存在、主动进行且具有环境依赖性的生存策略。