What is a Vacancy Chain?

In a vacancy chain, when a new resource becomes available to a population, it is claimed by a first individual who then leaves behind its old resource. This old resource is then taken by a second individual who relinquishes its old one in turn, and so on. For example, if a snail dies, its shell may be taken by a hermit crab that abandons the snail shell it used to live in. This discarded shell may be taken by a second hermit crab, etc. Eventually a vacancy chain ends, perhaps when the shell left behind by a crab is in such bad shape that no other crab wants it. Vacancy chains are also common in humans, and this is the process through which people often obtain houses, apartments, cars, and certain kinds of jobs. Where they occur, vacancy chains allow several individuals to move up to new and better resources. Unlike other kinds of competition where one individual succeeds in getting something (like food) and other individuals do not, in a vacancy chain one individual’s success allows other individuals to be successful too.

For a non-technical discussion of vacancy chains in humans and hermit crabs, see this article.

(To see an actual vacancy chain in the field click on the video below and to see how one individual’s success helps other individuals, click on the animation.)