What is the most unusual characteristic of food webs in agroecosystems?

Agroecosystems are man-made ecosystem, utilized and created by humans to grow crops. In agroecosystems only those floral and faunal species are rared which are important to humans other naturally growing wild species are eliminated by choice. A food web is a interconnection of food chains. A food chain is a linear sequence of transfer of food when one organism is consumed by other. Therefore, food webs in these agroecosystems are manipulated according to human needs which allows only the desired plants species to grow, desired insects species to pollinate flowers, makes the crop pest resistant by killing insects, tillage of soil before seeds are sown. Hence, food webs in agroecosystems exhibit unusual characteristics different from natural ecosystem.