Abstract
An understanding of the balance of interspecific competition and the physical environment in structuring organismal communities is crucial because those communities structured primarily by their physical environment typically exhibit greater sensitivity to environmental change than those structured predominantly by competitive interactions. Here, using detailed phylogenetic and functional information, we investigate this question in macrofaunal assemblages from Northwest Atlantic Ocean continental slopes, a high seas region projected to experience substantial environmental change through the current century. We demonstrate assemblages to be both phylogenetically and functionally under-dispersed, and thus conclude that the physical environment, not competition, may dominate in structuring deep-ocean communities. Further, we find temperature and bottom trawling intensity to be among the environmental factors significantly related to assemblage diversity. These results hint that deep-ocean communities are highly sensitive to their physical environment and vulnerable to environmental perturbation, including by direct disturbance through fishing, and indirectly through the changes brought about by climate change.
Highlights
Competition between species has long been recognized as an important factor determining the ecological diversity and structure of organismal communities [1,2,3,4]
An understanding of the balance of interspecific competition and the physical environment in structuring organismal communities is crucial because those communities structured primarily by their physical environment typically exhibit greater sensitivity to environmental change than those structured predominantly by competitive interactions
Explanatory terms included in each generalized additive models (GAMs) were refined by backwards stepwise selection considering variable p-values and model Akaike information criterion (AIC) until a minimum AIC value was reached
Summary
Competition between species has long been recognized as an important factor determining the ecological diversity and structure of organismal communities [1,2,3,4]. To characterize the functional structure of the sampled peracarid assemblages, we constructed a dendrogram (figure 2b) describing the functional similarity of sampled families based on their scoring for a selection of traits (electronic supplementary material, table S3). To investigate relationships between the PSV/FSV of sampled peracarid assemblages and the prevailing environmental conditions, we examined the following environmental parameters: bathymetry (depth, slope, aspect, seafloor rugosity, bathymetric position index (BPI)); fishing intensity (vessel monitoring system (VMS) signal density and total trawl length per km2); geological context; seafloor sediment particle size ( percentage clay/silt/sand); carbon availability (percentage inorganic, organic and total carbon, surface chlorophyll a and particulate organic carbon (POC) concentrations, modelled transport of POC to depth); physical oceanographic variables (temperature, salinity and current speed); and month and year of sample collection. Explanatory terms included in each GAM were refined by backwards stepwise selection considering variable p-values and model AIC until a minimum AIC value was reached (see the electronic supplementary materials for additional detail relating to the methodology employed by this study)
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