DOI: 10.5061/dryad.c2fqz6153
title: Changes in stream food web structure across a gradient of acid mine drainage increases local community stability

description: Understanding what makes food webs stable has long been a goal of
 ecologists. Topological structure and the distribution and magnitude of
 interaction strengths in food webs have been shown to confer important
 stabilizing properties. However, our understanding of how variable species
 interactions affect food web structure and stability is still in its
 infancy. Anthropogenic stress, such as acid mine drainage, is likely to
 place severe limitations on the food web structures possible due to
 changes in community composition and body mass distributions. Here, we
 used mechanistic models to infer food web structure and quantify stability
 in streams across a gradient of acid mine drainage. Multiple food webs
 were iterated for each community based on species pairwise interaction
 probabilities, in order to incorporate the variability of realistic food
 web structure. We found that food web structure was altered systematically
 with a 32-fold decrease in the number of links and a 2-fold increase in
 connectance across the gradient. Stability generally increased 6-fold with
 increasing acid mine drainage stress, regardless of how interaction
 strengths were estimated. However, the distribution of the stability
 measure, s, for some impacted communities separated into clusters of
 higher and lower magnitude depending on how interaction strengths were
 estimated. Management and restoration of impacted sites needs to consider
 their increased stability, as this may have important implications for the
 re-colonization of desirable species. Furthermore, active species
 introductions may be required to overcome the internal ecological inertia
 of affected communities.
description: <strong>community_data.csv:</strong> Benthic
 macroinvertebrates were collected with Surber samples (0.06
 m<sup>2</sup>) from New Zealand streams across a gradient of
 acid mine drainage stress. Fish were also sampled using electrofishing
 methods. All animals collected had their body lengths measured and their
 biomass estimated using published length-weight regressions. Dry weights
 and density values are average estimates per taxa. 
 site: site identifier. Corresponds to observations in
 "amd_gradient.csv" taxa: Taxonomic name of
 sample. Fish are identified to species, most aquatic insects are
 identified to genus.  dw.g: taxa average estimated dry
 weight, in grams  density_m2: taxa average estimated
 densities, in m<sup>2</sup> rel.ab: taxa
 relative abundance per site
 <strong>amd_gradient.csv</strong>: The acid mine
 drainage stress gradient was determined with PCA. The site scores from PC
 axis 1 were used to infer level of stress (higher values represent greater
 AMD stress).  site: site identifier, corresponds with
 "community_data.csv" amd_stress: site
 specific scores from PC axis 1. negative values are unimpacted, and
 increasing positive values represent increasing AMD stress
 <strong>niche_model_parameters.csv</strong>: The
 model parameters are coefficient estimates for a statistical model of
 interaction probabilities based on predator-prey body size relationships.
 The statistical model used is described in Bartomeus et al. (2016
 Functional Ecology). Data from Broadstone stream and Tadnoll Brook
 (Woodward et al. 2010, Advances in Ecological Research) were used to
 parameterize the model.  coefficient: the model
 coefficient estimate: the estimated value of the
 coefficient from the parameterized model.