165 Sustainable food systems require livestock.

Abstract Sustainable food systems can be defined as those that deliver nutritional security to all in a way that economic, social, and environmental bases used to generate food for current and future generations are not compromised. Such systems need to succeed across various climates, soil types, topographies, cultures, and states of economic development. As with ecosystems that depend upon multiple trophic levels of biotic factors (e.g., microorganisms, plants, animals, fungi), agroecosystems that provide food depend upon different trophic levels to enhance provisioning, regulating, cultural, and supporting ecosystem services. Livestock specifically can contribute to ecosystem services and disservices depending upon management decisions, location, and concentration relative to resource (e.g., forage) availability. From a macro perspective, livestock are essential to food systems. Livestock upgrade plant protein quality for human consumption via upcycling plant sourced feedstuffs, and can enhance the availability of essential micronutrients in the food supply via meat, milk, egg, and fish products. Additionally, ruminant livestock production can take place on landscapes unsuitable for cultivated crop systems, providing food production while supporting wildlife habitat, recreational value, soil carbon storage, and water filtration among other goods and services. Livestock production is beneficial in enhancing nutrient cycling through agricultural systems and offsetting the requirement for synthetic fertilizers via connecting manure nutrients to cultivated and other food cropping systems. Economically, livestock production supports the livelihoods of over 1 billion people across the world. Livestock production also contribute to ecosystem disservices, such as greenhouse gas emissions and through water use that exceeds recharge rates in water scarce regions. Ultimately, when assessing the ecosystem services and disservices of livestock systems, globally, livestock are a clear net benefit to humanity. However, further improvements in production systems via management, genetics, herd/flock health, and nutrition can be made to minimize negative impacts and enhance positive contributions of livestock.