Do you bend or break? System Dynamics in resilience planning for food security

This paper discusses our experience in using system dynamics to facilitate resilience planning for food security in rural communities that are exposed to ever‐increasing climatic pressures in Guatemala. The social–ecological systems literature is rich in examples where policies to enhance resilience are deduced from factors generally accepted to be present in resilient systems (e.g. redundancy, connectivity and polycentrism). This deductive approach risks being overly simplistic. As an alternative, this paper explores how insights from analysing the structure–behaviour relationship of complex dynamic systems can be used to generate tailored policies. The results show that stability in food systems is mainly driven by key strategic resources that moderate the effects of environmental changes on food availability and affordability. Moreover, our experience highlights the importance of analysing mechanisms that determine a system's behaviour while and after the system is affected by a disturbance to formulate effective resilience policies

Organic agriculture promotes evenness and natural pest control

Human activity can degrade ecosystem function by reducing species number (richness) and by skewing the relative abundance of species (evenness). Conservation efforts often focus on restoring or maintaining species number reflecting the well-known impacts of richness on many ecological processes. In contrast, the ecological effects of disrupted evenness have received far less attention, and developing strategies for restoring evenness remains a conceptual challenge. In farmlands, agricultural pest-management practices often lead to altered food web structure and communities dominated by a few common species, which together contribute to pest outbreaks. Here we show that organic farming methods mitigate this ecological damage by promoting evenness among natural enemies. In field enclosures, very even communities of predator and pathogen biological control agents, typical of organic farms, exerted the strongest pest control and yielded the largest plants. In contrast, pest densities were high and plant biomass was low when enemy evenness was disrupted, as is typical under conventional management. Our results were independent of the numerically dominant predator or pathogen species, and so resulted from evenness itself. Moreover, evenness effects among natural enemy groups were independent and complementary. Our results strengthen the argument that rejuvenation of ecosystem function requires restoration of species evenness, rather than just richness. Organic farming potentially offers a means of returning functional evenness to ecosystems