Monitoring anthropogenic impacts is essential for managing and conserving ecosystems, yet current biomonitoring approaches lack the tools required to deal with the effects of stressors on species and their interactions in complex natural systems.Ecological networks (trophic or mutualistic) can offer new insights into ecosystem degradation, adding value to current taxonomically constrained schemes. We highlight some examples to show how new network approaches can be used to interpret ecological responses.Synthesis and applications. Augmenting routine biomonitoring data with interaction data derived from the literature, complemented with ground-truthed data from direct observations where feasible, allows us to begin to characterise large numbers of ecological networks across environmental gradients. This process can be accelerated by adopting emerging technologies and novel analytical approaches, enabling biomonitoring to move beyond simple pass/fail schemes and to address the many ecological responses that can only be understood from a network-based perspective.

22When we subsequently perturbed the webs by simulating species loss in silico, the rewired drought 23 webs were as robust as the larger, undisturbed webs. Our research unearths previously unknown 24 compensatory dynamics arising from within the core that could underpin food web stability in the 25 face of environmental perturbations. 26Many areas of the world are becoming increasingly prone to drought 1,2 and declining precipitation 27 coupled with rising demand for water could threaten the integrity of freshwater ecosystems across the 28 globe 3,4 . In rivers and streams, the elimination of sensitive species could potentially undermine community 29 structure and ecosystem functioning 7-9 , yet how this affects food web stability -at both substructural and 30 whole-network levels 10 -has yet to be fully elucidated. Responses to climate change are frequently 31 interpreted autecologically, through analysis of individual species traits 11 , but these ignore the role of 32 species interactions, foraging dynamics and potential compensatory mechanisms such as resource 33 switching, that determine food web stability. Synecological approaches that can address changing species 34 interactions in the context of the whole food web [12][13][14] , and hence the potential trophic mechanisms behind 35 community-level responses 15,16 , remain scarce. In addition, there are non-random substructures in food 36 webs which could underpin their responses to perturbations 17 . Recent advances in network science have 37 linked the presence of a cohesive "core" of closely interacting nodes and a loosely connected 38 "periphery" 5,[18][19][20] to the stability of complex (non-ecological) networks 21,22 . The significance of this for 39 food web responses to an environmental perturbation -drought -is reported here for the first time. 40The network "core" is a cohesive group of highly connected nodes that governs the functional 41 attributes of a wide range of complex systems 18 . It determines system robustness because densely 67To test our hypotheses, we applied a novel graph profiling technique 5 to characterise the cores of our 68 eight highly-resolved replicate food webs 10,26 . To generate a graph profile for a web, nodes were ranked by 69 their degree (number of links). Starting from the highest degree node, we examined the interconnectedness 70 among the high degree nodes as those of a lower rank were included sequentially. A point is reached 71 4 whereby the connectivity among the high degree nodes peaks, reflecting the cohesiveness in the core and 72 defining the core boundary, and which is followed by generally decreasing connectedness thereafter. The 73 rest of the nodes form the periphery, which is only loosely connected to the core, and contains few or no 74 links among its constituents. After characterising the core/periphery structure, we then measured the 75 density of interactions within the core and across the web using the "rich-club" coefficient 27 . To gauge the 76 level of organisation in the core/periphery s...

Sustainable management of ecosystems and growth in agricultural productivity is at the heart of the United Nations' Millennium Development Goals for 2030. New management regimes could revolutionise agricultural production, but require a full evaluation of potential risks and opportunities. Replacing existing conventional weed management with genetically modified, herbicide-tolerant crops (GMHT), for example, might reduce herbicide applications and increase crop yields, but remains controversial owing to concerns about potential impacts on biodiversity. To date, such new regimes have been assessed at the species or assemblage level, whereas higher-level ecological network effects remain largely unconsidered. Here, we conduct a large-scale network analysis of invertebrate communities across 502 UK farm sites to GMHT management in different crop types. We find that network-level properties were overwhelmingly shaped by crop type, whereas network structure and robustness were apparently unaltered by GMHT management. This suggests that taxon-specific effects reported previously did not escalate into higherlevel systemic structural change in the wider agricultural ecosystem. Our study highlights current limitations of autecological assessments of effect in agriculture in which species interactions and potential compensatory effects are overlooked. We advocate adopting the more holistic system-level evaluations we pioneer here, which complement existing assessments for meeting our future agricultural needs.