Ecosystems have many trophic levels of organisms including primary producers, herbivores, omnivores, carnivores; parasites, and decomposers. Agroecosystems are ecosystems managed for food and fiber production that have less diversity and typically fewer trophic interactions than natural ecosystems. But diverse organisms and their trophic interactions provide important functions in agroecosystems including for instance, decomposition and nutrient cycling; plant pollination, and pest suppression. Organisms that reduce agricultural productivity and quality and are referred to as agricultural pests; these include weeds pathogens, insects and other herbivorous organisms. Mammals that graze or browse crops (ex. deer and rodents), and other arthropod species such as mites and slugs (mollusks), can also reduce crop yields through grazing and seed predation.