Homes for hermits: temporal, spatial and structural dynamics as transportable homes are incorporated into a population

摘要

Understanding the process by which limiting resources are incorporated into populations is a major goal of ecology. While many studies have examined this dynamic process using essential resources like homes, few of these studies have involved homes that can be transported by their occupants. This study introduced over a thousand transportable homes into a population of terrestrial hermit crabs Coenobita compressus, animals that carry their homes with them wherever they travel. These new homes were tracked between years to test key predictions about the temporal dynamics the homes would generate, and the spatial and structural changes the homes would undergo as they were used by the population. When moving into new homes, crabs dropped off their old homes directly at the exchange site, and the number of such traded-in homes peaked rapidly in time. Traded-in homes were under half the diameter of new homes, a difference apparently magnied by social formations involving vacancy chains. After crabs moved into new homes, they carried the homes away from the exchange site. The following year, these homes were displaced a distance four orders of magnitude times their diameter, thus penetrating extensively through the population. Between years, crabs also remodeled the internal architecture of the homes, creating homes that were more spacious and less of a burden to carry. These results suggest that transportable homes generate novel ecological dynamics along temporal, spatial and structural dimensions, which are a direct consequence of their transportability. ‘I live on land and walk about, but always home, in or out.’ – Virgin Island riddle Introduction Many populations of organisms may be limited by the availability of life-sustaining resources. Understanding how such resources are incorporated into populations requires studying the dynamic processes that occur from the time resources rst enter populations onwards across the lifetime of their use (Levin, 1992). Experimental studies have sought to explore such resource dynamics by introducing items that are critical for survival and reproductive success, and then tracking how these resources are used across time and space. Studies of vertebrates, for instance, have introduced large quantities of homes, such as shelters in mammal populations or nestboxes in bird populations, and have then traced the dynamics of these limiting resources as they are reused across successive occupants (reviewed in Newton, 1994; Lambrechts et al., 2010). Typically, however, introduced homes are immobile, xed in one location. Yet, if homes were not immobile but rather were subjec