Species contributions to ecosystem stability change with disturbance type

Simultaneous exposure to multiple stressors complicates the challenge of predicting ecological responses to global environmental change. Here, we show that the contributions of individual species and functional groups to the overall stability of ecosystems can be modified by the presence of different stressors, both individually and in combination. By disturbing natural rocky shore communities with nutrients and sediments and simulating extinction of predatory whelks and grazers, we also found that consumers can simultaneously stabilise and destabilise communities along different stability dimensions, irrespective of their trophic position. Our results suggest that our experimental disturbances influenced consumer contributions to stability indirectly by modifying the interactions between consumers and macroalgae in different ways. These findings merit further exploration in different systems exposed to a range of different stressors to better understand how perturbations of different kinds can modify the multifaceted contributions of species to the overall stability of ecosystems.

Methods
This dataset contains species abundance matrices for monthly surveys of experimental plots at Rush, Co. Dublin, Ireland (53.524° N, 6.078° W) over 15 months from August 2015. We measured the percent cover of macroalgae monthly using a 25 x 25 cm quadrat with 64 intersections, positioned centrally within cages to avoid sampling edge effects. Species present within the quadrat but not occurring underneath any of the intersections were assigned a cover value of 1%. We used the dataset to quantify four components of ecological stability, separately for both total algal cover (as a proxy for total algal biomass) and assemblage structure as measures of, respectively, functional and compositional stability. Please see Table 1 and methods section in the associated manuscript for details on calculating stability measures. R scripts for calculating stability measures and producing figures within the manuscript can be found here: https://github.com/lydiajanewhite/rush-paper-analysis