DOI: 10.5061/dryad.vmcvdncrn
title: Large-scale multi-trophic co-response models and environmental control of pelagic food webs in Québec lakes

description: Environmental heterogeneity plays a fundamental role in driving species
 distributions by, for one, fostering niche dimensionality. Within lake
 ecosystems, species distributions and concordance patterns are driven by
 both local and regional heterogeneity, though their relative importance
 across trophic levels has rarely been explored. We developed a statistical
 framework to compare responses of taxa from different trophic levels
 to abiotic factors and determine how thisaffected
 multi-trophic network structures.In particular, we used multi-species
 concordance modelling (Concordance Analysis and RV coefficient) to
 determine species associations and correlations within and among three
 trophic levels (phytoplankton, zooplankton and fish communities
 sampled across 49 southern Québeclakes, covering eight
 hydrological regions). We then used Multiple Factor Analysis, Latent
 Variable Modelling and Local Contributions of sites to Beta Diversity to
 assess the relative importance of major environmental gradients in
 structuring species co-responses and species interaction turnover across
 the landscape. Our analyses confirmed that concordant species within each
 trophic level varied jointly or segregated into different pelagic food
 webs in Québec lakes where important acidification and eutrophication took
 place. Somekeynote species were indicators of different food web
 compartments and distinguished groups of lakes along multiple
 environmental niche dimensions. Among the three trophic levels examined,
 zooplankton depicted the highest proportion of species concordance and
 appeared to act as a trophic linkage between phytoplankton and
 fish. Ultimately, the losses or gains in species richness and
 species interactions were strongly driven by environmental gradients.This
 study provides for the first time a combined analysis of the effects of
 environmental heterogeneity on ecological communities belonging to three
 trophic levels sampled near simultaneously across an 800 km broad
 lacustrine landscape. The new framework developed in this study has
 a great potential to better understand the complex response of
 aquatic ecosystems in a world increasingly affected by multiple,
 cumulative stressors. The file provided herein is an RStudio project
 containing all data files and R script to run the statistical analyses and
 reproduce figures of the study. 
description: Fifty-four (54) Canadian Shield lakes were sampled throughout southern Québec, north of the St. Lawrence River and south of latitude 52ºN, during summer 1982. The lakes are distributed along an 800 km south-west to north-east longitudinal geographical range (78°to 63° W) and cover eight hydrographical regions. The present study was restricted to 49 lakes with complete data for asuite of morphometric, physical, chemical, and biotic variables, including three trophic levels (phytoplankton, zooplankton and fish communities). Plankton and fish communities were sampled during July and August 1982, thus capturing a key period of anthropogenic acidification and consequently one of the strongest spatial gradients in natural and anthropogenic lake acidity experienced in the region. To minimize the effect of the seasonal development on plankton communities, sampling started at successive times in the eight regions following the west-to-east geographic and climatic axis gradient over a period of 1 month. Phytoplankton species counts (87 species across all sites) were expressed as cells per millilitre; zooplankton species counts (34 species) were expressed as numbers of individuals per cubic metre and converted to biomass (milligrams per cubic metre) using specific dry mass relationships; fish counts (18 species) were expressed in abundances (catch per unit effort). Environmental variables examined provided information on the geography (latitude, longitude, and altitude), morphometry (lake and catchment areas, lake order, maximum and relative depths, length, width, and volume), and water quality (pH, ions, metals, alkalinity, alkalinity: sulfate ratio, organic and inorganic carbon, conductivity, transparency, colour, and the morphoedaphic index) of each study site.