Spatial Relationships between Polychaete Assemblages and Environmental Variables over Broad Geographical Scales

Lisandro Benedetti-Cecchi,Gabriela Palomo,Claudio Lardicci,Gerhard Pohle,Elena Maggi,Angela Mead,Yoshihisa Shirayama,Melisa Wong,Juan Cruz-Motta,Ann Knowlton,Brenda Konar,Tom Trott,Katrin Iken,Laura Tamburello,Patricia Miloslavich,Alberto Castelli,Simon Thrush

doi:10.1371/journal.pone.0012946

Abstract

This study examined spatial relationships between rocky shore polychaete assemblages and environmental variables over broad geographical scales, using a database compiled within the Census of Marine Life NaGISA (Natural Geography In Shore Areas) research program. The database consisted of abundance measures of polychaetes classified at the genus and family levels for 74 and 93 sites, respectively, from nine geographic regions. We tested the general hypothesis that the set of environmental variables emerging as potentially important drivers of variation in polychaete assemblages depend on the spatial scale considered. Through Moran's eigenvector maps we indentified three submodels reflecting spatial relationships among sampling sites at intercontinental (>10000 km), continental (1000–5000 km) and regional (20–500 km) scales. Using redundancy analysis we found that most environmental variables contributed to explain a large and significant proportion of variation of the intercontinental submodel both for genera and families (54% and 53%, respectively). A subset of these variables, organic pollution, inorganic pollution, primary productivity and nutrient contamination was also significantly related to spatial variation at the continental scale, explaining 25% and 32% of the variance at the genus and family levels, respectively. These variables should therefore be preferably considered when forecasting large-scale spatial patterns of polychaete assemblages in relation to ongoing or predicted changes in environmental conditions. None of the variables considered in this study were significantly related to the regional submodel.

Highlights

Explaining the causes of variation in biodiversity at multiple spatial scales is a major goal of ecology
We examined the spatial relationships between rocky shore polychaete assemblages and environmental variables over broad geographical scales, using the database compiled by the Census of Marine Life NaGISA (Natural Geography of In Shore Areas) research program
Three submodels, reflecting variation at different spatial scales, originated from each of the two spatial weighting matrices selected by the AICc criterion

Summary

Introduction

Explaining the causes of variation in biodiversity at multiple spatial scales is a major goal of ecology. There is ample evidence indicating that small-scale spatial heterogeneity is ubiquitous in natural populations and assemblages (e.g., [6]). Some of the processes accounting for local spatial patterns may affect assemblages at larger scales. Local processes such as biotic interactions, behavior and fine-grain environmental heterogeneity may propagate in space to generate large-scale patterns [7,8]. When patterns in species richness are of concern, regional processes, such as geographic, historic and evolutionary events may determine local species pools and their interactions [9]. The analysis of spatial patterns makes sense only within the geographic limits of focal taxa distribution, setting a natural upper bound to the breadth of ecological spatial analyses

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Results

Conclusion