The hermit crab–shell relationship through the lens of interaction networks: The use of network metrics and species role across communities

Abstract

Hermit crabs are among the most unique crustaceans because they have a non-calcified pleon, and they often use empty gastropod shells for shelter and protection. The lack of an adequate shell impacts their growth, reproduction and other population features especially because the shell resource might not be found for the entire population or community. This study focuses on the relationship between hermit crabs and their shells using network metrics. We analysed the nestedness, modularity, network specialisation, species specialisation and species role in eight hermit crab communities from two different types of substrate (rock and soft bottom). Most of these communities had a modular and non-nested pattern. Some communities presented different specialisation levels in terms of resource use (generalist or specialist) with species showing different roles across communities. These patterns could be related to the intra-/interspecific competition mechanism and by the resource (shell) usage pattern in the different regions. According to species roles, some species characterised as connectors can be addressed as conservation targets. The network approach in hermit crab/shell relationship proved to be an important tool in assessing their interaction in a community level.

Morphometric traits as drivers for module structures and species specialization: a study about the hermit crab–gastropod networks from three different regions on the Brazilian coast

“…We used networks of three hermit crab communities, in which network metrics and properties were already described by da Silva et al. (2020). In these communities, hermit crabs and shell resources are nodes, and the interactions are the links between them.…”

“…Network ecology focuses on how species interact with resources and other species in a given community (Eklöf & Allesina, 2017). These interactions can have implications to each species involved, as they can be positive, e.g., pollination and seed dispersal (Correia et al., 2017; Donatti et al., 2011), negative, e.g., parasitic (Sfair et al., 2018), and also they can benefit one partner while not affecting the other (Veiga, 2016). This latter type of association is called commensalism and includes metabiosis, which is an interaction where only one of the interacting species is living and subject to adaptation (Veiga, 2016).…”

“…Hermit crabs strategies to acquire new shells from others hermit crab occur mainly by contests over gastropod shells (with an “attacker” and a “defender”) (Briffa & Elwood, 2001; Lane & Briffa, 2020) and also interacting among themselves to exchange resources, through a clustering behavior known as the “shell exchange market” theory (Gherardi & Vannini, 1993). Recently, these vital interactions have caught the attention of researchers through network ecology and its properties (da Silva et al., 2020; Rodrigues et al., 2020; Santos et al., 2021). Network ecology provides reliable information about this relationship between hermit crab/shell resource through metrics such as nestedness, modularity, niche overlap, network specialization and species specialization (Bascompte et al., 2003; Borthagaray et al., 2014; Dormann & Strauss, 2014; Fortuna et al., 2010; Strauss & Fuiman, 1985).…”

“…Structural properties of interaction networks, such as nestedness and modularity, are influenced by species abundance, species traits and resource properties which has been studied in various types of interactions (Ballarin et al., 2019; Calatayud et al., 2017; Chamberlain & Holland, 2009; Donatti et al., 2011; González‐Castro et al., 2015; Sazatornil et al., 2016; Sfair et al., 2018; Stang et al., 2006; Tur et al., 2015; Vizentin‐Bugoni et al., 2016). However, the factors underlying the structural properties of the relationship between hermit crabs and gastropod–shells that was recently evaluated through the network approach remain unvisited (see Rodrigues et al., 2020 and da Silva et al., 2020). Although both studies point to a modular and non‐nested structure, it remains unclear which processes (neutral and/or niche) rule hermit crab and gastropod–shell interactions and what is the role of abundance and functional traits in generating a compartmentalized network.…”

“…Therefore, the present work aimed to assess if morphometric traits of hermit crab influence the network features in three of the networks described by da Silva et al. (2020). We assessed if morphometric traits could explain metrics such as modularity and species specialization in a descriptive and correlative manner with empirical data.…”