The study of diseases in humans and animals is the field of microbiology. Epidemiologists working in the field of microbiology monitor the prevalence of disease in populations. Scientists study how the immune system protects the body in the field of . In the field of , however, a variety of approaches are used to describe microbial diversity in terms of relationships between organisms and their environments. Merging both medical and microbial ecology, the field of microbiology concerns the role of microbes in crop production and as pesticides. Another area that parallels agricultural microbiology is the study of microbial spoilage, which is part of the field of microbiology. Researchers in the field of microbiology develop ways to exploit the metabolic abilities of microbes to generate valuable products.