They simply sense changes in their environment, as for example when the mound's wall has been damaged, altering the circulation of air.

句末的现在分词短语作状语，有一种是以前面的分句内容为逻辑主语的。例如：

The mound's wall was damaged, and that altered the circulation of air.

The mound's wall was damaged, which altered the circulation of air.

（非洲蚂蚁的蚁穴高出地面呈土丘状（mound），穴壁的破坏会改变空气的流动。）

这个句子中的which引导的非限制性定语从句补充说明主句内容，which的先行项为主句。由于从句谓语alter和主句谓语具有同时性，which的内容为主句，正式语体的书面语中就可以省去which，将从句的谓语改为现在分词短语作补充性状语，本句中分词短语具有结果意义。

The mound's wall was damaged, altering the circulation of air.