DOI: 10.5061/dryad.pk0p2ngr0
title: Guadeloupe Snails Metacommunity

description: Metacommunity structure reflects the interplay of various processes,
 including niche filtering, extinction/colonization, and interspecific
 interactions. Spatial patterns of species distributions are often analyzed
 to infer these processes. However, such inferences rely on often
 unrealistic equilibrium assumptions, and remain ambiguous, as different
 processes can produce similar patterns. Temporal data may improve these
 inferences. For example, stochastic species turnover may occur in local
 communities, while, on the long run, temporal changes are kept within
 limits set by locally available niches. Our objective is to explore how
 the joint analysis of spatial and temporal patterns can clarify the
 contribution of different processes to metacommunity structure. We
 recorded the occurrences of 21 freshwater mollusc species, and
 environmental data, in 250 sites over 17 successive years in a network of
 ponds in Guadeloupe (Lesser Antilles). We analyzed variation in α and
 β-diversities in space and time, and used a joint-species distribution
 mode to characterize species-environment and species-species
 relationships. Local communities showed pronounced temporal variation
 reflecting both imperfect species detection and true stochastic species
 turnover. On the long term however, local communities were largely
 controlled by niche filtering along two main environmental gradients, one
 driven by site connectivity, the other by hydrological stability and
 aquatic vegetation. Two gastropod clades, caenogastropods and pulmonates,
 showed contrasted spatio-temporal distributions resulting from different
 responses to these gradients, and these distributions seemed little
 altered by interspecific competition. Our study illustrates the benefit of
 using spatiotemporal metacommunity data to discern long-term impacts of
 niche filtering and species interactions behind short-term stochasticity.
description: Data collection occurs every years since 2001, usually in
 January/February (the beginning of the dry season). Each site was surveyed
 by three persons for 15 minutes, to record mollusc species and
 environmental characteristics. Environmental values were averaged over
 years to produce long-term site-specific values (file
 "<strong>cov_unscale_no_habit</strong>"). An
 additional variable, included in this file is the "Stability
 Index" : computed from variability of various variables and
 dessication probability - and representing the long-term hydrological
 regime (i.e. contrasting unstable sites with high probability of
 dessiccation, to stable permanent water bodies). In addition, the
 '<strong>sites_informations</strong>' file provides
 sites' positions (long/lat) as well as sites' types (i.e. ponds,
 river, back-mangroves). Two year-specific (temporal) variables are given
 in file "<strong>pluvio</strong>" - the cumulative
 rainfalls during the rainy season (RS) and during the little rainy season
 (LRS), which are averaged over five Guadeloupean meteorological
 stations. Species presences were recorded in wet sites,
 and a random subset of sites (ca. 30 by year) was re-sampled to estimate
 species detection probabilities
 (<strong>presence.zip</strong>). The
 '<strong>dry_final</strong>' file provides the
 matrix of site's states (i.e. dry – 1 or wet - 0, or a probability of
 being dry). Species presences (i.e. detection) are in
 the <strong>GT_presence.RDS</strong> compressed file (use
 readRDS() from R) – 0 are NA, 1 absence, and 2 presence.
 All analyses are describe in
 <strong>Guadeloupe-Snails---first-part.html</strong>, and
 <strong>Guadeloupe-Snails---second-part--HMSC-.html.
 </strong>Exact content of data files are given in the REAMDE.txt
 file. Additional scripts : <strong>run_HMSC.R</strong> : run
 HMSC model, <strong>R2_hmsc.R</strong> : compute R2 for
 training & validation datasets,
 <strong>null_dissimilarities.R</strong> : compute null
 expectation for among-community dissimilarity.
description: Programs : R and JAGS