Is Variety More than the Spice of Life? Diversity, Stability and Sustainable Agriculture by David A. Cleveland Center for People, Food and Environment Tucson, Arizona Who does not delight in the multitude of different kinds of beetles or wildflow- ers, in heaps of many colored potatoes, beans or com cobs at harvest, or in the costumes, rituals or fanning techniques of different ethnic groups? Many of us find the rich variety of life on this planet, the result of biological and cultural evo- lution over aeons, emotionally and intel- lectually exciting. However, at this point in time, when we face potentially cata- strophic environmental degradation, a huge and growing human population, and widespread human conflict and mal- nutrition, is diversity really useful? A consensus seems to be emerging which recognizes that biological diver- sity is essential for the continued func- tioning of the planet as we know it (i.e., in maintaining the composition of the atmosphere or the generation and main- tenance of soils [e.g., Ehrlich and Wilson 1991; NRC 1992:12-18]). Ethical and aesthetic reasons and direct economic benefits are also widely accepted as argu- ments for conserving biodiversity. In many cases, such concerns underlie the alarm over the increasing rate of destruc- tion of biodiversity (Ehrlich and Wilson 1991;NRC 1992:31-34). Theyalsosug- gest that there is a direct relationship between diversity and stability. Put sim- ply from a human-centered perspective, we don't want the world to change too much, or we won'tbe able tolivehere any longer. Many ecologically- and socially-ori- ented scientists also claim that a direct relationship exists between stability and diversity in agriculture, and they contend that the conservation of this diversity is essential for our future(e.g., Cooper etal. 1992;Pimenteletal. 1992). Small-scale, low-input, indigenously-based agricul- ture is usually more ecologically, biologi- cally and culturally diverse than large- scale, high-input industrial agriculture (Cleveland and Soleri 1991:286-293). The diversity present in indigenous agri- culture at crop, field and regional levels offers greater yield stability than does the less diverse industrial-style agriculture. While it may offer higher levels of pro- "What role do biologi- cal and cultural diversity play in agricultural stability and in the development of sustain- able agriculture?" duction under certain conditions, the lat- ter has only been in existence for one century. Indeed, an inverse relationship may exist between diversity and stability on theonehand, andproductionmaximi- zation on the other. This means that optimal diversity, not maximum produc- tion, is the key to sustainable agriculture. More conventional, production-oriented agricultural scientists, however, disagree with this assertion. Although they recog- nize trade-offs among diversity, stability and production, they argue that the in- creasedproductionmadepossiblethrough industrial agriculture, even with the sub- sequent loss of diversity, is the only pos- sible route to agricultural development (e.g., Anderson and Hazell 1989a). In this article I examine the following questions. What role do biological and cultural diversity play in agricultural sta- bility and in the development of sustain- able agriculture? Is the conservation of this diversity really essential for our fu- ture? Diversity and Stability in Ecology and Agriculture Because both social and natural agri- cultural scientists often borrow ecologi- cal concepts, I begin with a brief consid- eration of the relevance of ecology for understanding the relationship between stability and diversity in agriculture. The idea that diversity begets stability became widespread in ecology in the 1950s. In addition, "the notion that greater community diversity is associ- ated with increased stability was among the most influential beliefs in ecology from the 1960s until the mid 1970s, reaching the status, in some cases, of a 'coreprinciple' (McNaughton 1988:204; also see Pimm 1991:6-9)." This belief came under attack in the early 1970s. May'smathematicalmodels showed that growing complexity augments fluctua- tion and hence increases community in- stability (see McNaughton 1988; Pimm 1991). However, May made the point that his models applied to random com- plexity. He suggested that real-world natural ecosystems might be mathemati- cally atypical, an assertion which has stimulated much subsequent research supporting a direct relationship between diversity and stability (McNaughton 1988:204; Pimm 1991:9-11). The discussion of stability and diver- sity in ecology is often confusing. This confusion stems in part from the diffi- culty of comparing results on different temporal and spatial scales, and in part because there are many possible defini- tions of the concepts involved. For ex- ample, Pimm has identified five defini- tions of stability, threedefinitions ofcom- plexity (diversity) and three definitions of levels of organization used by ecolo- gists—for a total of 45 "possible ques- tions about the relationships between