The majority of farmers employ a combination of farming techniques. Mixed agriculture, with livestock and crops integrated into a single ecosystem, is very common in Asia, Africa and the Americas. Farmers are often highly dependent on animals as a key component of the farming system. The animals provide meat, milk, fuel, fertilizer, draft power, transportation and can be fed largely with agricultural waste products. Additionally, farmers are frequently engaged in a combination of agricultural and economic pursuits. They can barter for food or labor, sell agricultural products or work for others. The choice of cropping system can be based on several factors; climate, soil types, local economies, markets, availability of labor and land, knowledge base and traditions all influence the decision.