DOI: 10.5061/dryad.37pvmcvkg
title: Determinism and stochasticity in the spatial-temporal continuum of ecological communities: the case of tropical mountains

description: Ecological communities are assembled in a spatial-temporal continuum.
 However, we still have a poor understanding of the relative importance of
 different mechanisms structuring community composition (i.e.,
 beta-diversity) in space and time. In this study, we start by introducing
 a conceptual model that capitalizes upon the core-occasional species
 concept to predict that the assembly process in tropical mountains is
 driven by the deterministic turnover of core species in space via habitat
 sorting, but the turnover of occasional species through time via
 stochastic events of colonization and local extinctions. We then propose a
 general analytical framework that allows assessing these predictions by
 partitioning the total variance of a species-by-site-by-time matrix (i.e.,
 total beta-diversity) among its purely spatial (variation in space
 independent of time), purely temporal (variation in time independent of
 space), and spatiotemporal (i.e., variation across different sites across
 different moments in time) components. Through simulation models, we
 provided theoretical support that the proposed analytical framework is
 suitable to test the predictions derived from our conceptual model. We
 then used this framework to identify general patterns and quantify the
 relative importance of processes underlying the spatial and temporal
 organization of ten distinct insect metacommunities along a tropical
 elevational gradient. As predicted, we found that, across taxa, spatial
 beta-diversity was mainly explained by environmental variation alone: a
 pattern that indicates the spatial turnover of core species. In contrast,
 temporal beta-diversity could not be distinguished from the expectation of
 null models where communities are simply represented by random draws from
 species pools: a pattern that indicates a temporal turnover of occasional
 species within communities. Taken together, our findings illustrate how
 our conceptual model and quantitative framework can articulate a better
 understanding of community assembly in space and time.
description: Sampling was carried out in
 the Serra dos Orgãos National Park (22°27′49″S; 43°01′50″W), Rio de
 Janeiro, Brazil. The park is one of the most preserved remaining fragments
 of the Atlantic Rainforest (Castro 2018), one of the hottest hotspots of
 global biodiversity (Myers et al. 2000). Along a complete elevational
 transect that ranges from 100 to 2130 meters above sea level (MASL), two
 flight interception Malaise traps were placed every interval of
 approximately 150 MASL, summing up to 15 sampled elevations. The
 collecting bottle of each Malaise trap was replaced every month from
 December 2014 to November 2015, summing up to 360 samples (2 traps x 15
 elevations x 12 months). A data logger was placed next to each pair of
 traps to record hourly variation in climatic conditions (air temperature
 and relative humidity) over the entire sampling period. Insects captured
 in each sample were sorted at the species level by our team and external
 collaborators (see acknowledgments). We focused our study on ten
 relatively well-known families and subfamilies of beetles (Lampyridae,
 Cerambycidae, Carabidae, Phengodidae, Eumolpinae, Anthribidae) and wasps
 (Ichneumonidae: Metopiinae, Pimplinae; Braconidae: Mesostoinae,
 Meteorini/Meteorus ). We considered only the adults of
 the focal taxonomic groups in the final species-by-time-by-site matrices
 (i.e., a total of 6996 individuals from 549 species across taxa). As such,
 this dataset considers only the months with the highest activity of adults
 across all taxonomic groups (i.e., from December to February and June to
 August).