How rugged individualists enable one another to find food and shelter: field experiments with tropical hermit crabs

Abstract

Animals from invertebrates to humans benefit from information conspecifics make available, including information produced inadvertently. While inadvertent social information may frequently be exploited in nature, experiments have rarely been conducted in the wild to examine how such information helps animals in their natural ecology. Here I report a series of field experiments on free-living terrestrial hermit crabs (Coenobita compressus), showing how these asocial invertebrates learn the locations of their most essential resources, food and shelter, using inadvertent cues from conspecific competitors. Crabs have limited abilities to locate resources individually, but as they coalesce on a resource, their aggregation can be noticed by passing foragers, tipping them off about the discovery. Foragers were strongly attracted to experimentally simulated aggregations in which crabs were tethered to the same spot and in which the resources normally found beneath aggregations were excluded. Simulated aggregations of crabs whose shells were removed were likewise attractive, more than even these sought-after-shelters themselves. Experiments that simulated the chemical and visual cues of aggregations independently revealed that foragers oriented to aggregations primarily by sight, cueing in on the jostling competitive activity of the aggregation. Although crabs have not been selected to recruit others to newly discovered resources, their natural ecology has provided a setting where competitors regularly help one another by means of inadvertent social information.

Costs of a more spacious home after remodelling by hermit crabs

“…Additionally, remodelling produces lighter homes that are approximately two-thirds the home's original weight [8], which can save crabs energy while carrying their home [11], especially given the variable travel distances of their scavenging lifestyle [12,13]. Besides these benefits of remodelling, crabs may also be constrained in their opportunities for acquiring spacious, lightweight homes via alternative means.…”

Experimental identification of social learning in wild animals

“…Moreover, waggle dance studies illustrate how conflicting data can result because social information use can vary between individuals and conditions (Grüter & Farina, 2009;Sherman & Visscher, 2002). The techniques utilized in the study of honeybee social learning could be adapted to other animals, and the increasing number of studies uncovering social learning or social information use in invertebrate species that are relatively easily manipulated in field settings (Laidre, 2010;Leadbeater & Chittka, 2007) suggest that invertebrates will provide much useful information on the ecology of social learning.…”

Social networks predict patch discovery in a wild population of songbirds

“…Finally, and perhaps most simply, individuals may be attracted to inadvertent cues produced by feeding conspecifics or heterospecifics. Such coarse-level local enhancement has been shown in a wide range of taxa, including invertebrates, fish, mammals and birds [9,12,13], and is thought to be the mechanism by which most animals use social information when searching for food sites [12,14].…”

“…In the context of finding patchy food resources, social information refers to information used by naive individuals to locate resources that they have obtained via the behaviour of successful patch finders [9]. Three such behaviours are generally accepted to occur: recruitment at roosts or colonies, active recruitment to food and local enhancement.…”