Food web rewiring drives long-term compositional differences and late-disturbance interactions at the community level

<strong>Abstract</strong> Ecological communities are constantly exposed to multiple natural and anthropogenic stressors. Multivariate composition (if recovered) has been found to need significantly more time to be regained after pulsed stress compared to univariate diversity metrics and functional endpoints. However, the mechanisms driving the different recovery times of communities to single and multiple stressors remain unexplored. Here, we apply for the first time quantitative ecological network analyses to try to elucidate the mechanisms driving long-term community composition dissimilarity and late-stage stressor interactions at the community level. For this, we evaluate the effects of three stressors (two pesticides and nutrients) and their interactions in outdoor mesocosms containing a complex freshwater community. We found interactions strength reorganisation to be strongly related to compositional changes and identified post-disturbance interaction strength rewiring to be responsible for most of the observed compositional changes. Additionally, we found stressor interactions to be significant in the long term only when both interactions strength and food web architecture are reshaped by the stressors. We suggest that quantitative network analysis has the potential to unveil ecological processes that prevent long-term community recovery. <strong>Methods</strong> The dataset used in this study comes from an outdoor mesocosm experiment performed between April and July of 2019 at the facilities of the IMDEA Water Institute (Alcalá de Henares, Spain). A full factorial design was used with eight different treatments applied in a randomized fashion and three replicates per treatment. The treatments included: the insecticide chlorpyrifos (1 µg/L and absent), the herbicide diuron (18 µg/L and absent), nutrients (750 µg/L of N and 75 µg/L of P, not added), and their binary and tertiary interactions. The nutrients treatment started one month before the application of the pesticides. Since then, P and P were applied twice a week for the whole duration of the experiment. The freshwater community tested in the experiment was composed of phytoplankton, zooplankton, and macroinvertebrates, which were sampled one time before and several times after the pesticide application. However, for the purpose of this study, we focus on days -5 (initial condition), 15 (expected maximum effect) and 50 (expected recovery) relative to the pesticides’ application. Please see the "readme" sheet in the datafile for a description of the file structure and treatments abreviations.