is important as different genes give rise to important traits, such as nutrient composition, hardiness to different environments, resistance to pests, or ample harvests. Genetic diversity is decreasing due to agricultural modernization, changing land use and climate change, among other factors. (It is even possible that breeding narrowly for the pest- and disease-resistance necessary to deal with climate change will, itself, reduce agrobiodiversity.) Genetic diversity is not static but is constantly evolving in response to changes in the environment and according to human intervention, whether farmers or breeders. Species diversity Species diversity refers to the number and abundance of different species used for food and agriculture. The number of species considered to contribute to food alone ranges from 5,538 to 75,000 depending on definitions. A conservative estimate is that about 6,000 species are commonly used for food. Species diversity includes "the domesticated plants and animals that are part of crop, livestock, forest or aquaculture systems, harvested forest and aquatic species, the wild relatives of domesticated species, and other wild species harvested for food and other products. It also encompasses what is known as “associated biodiversity”, the vast range of organisms that live in and around food and agricultural production systems, sustaining them and contributing to their output." Agriculture is understood to include crop and livestock production, forestry, fisheries and aquaculture. Aquatic diversity is an important component of agricultural biodiversity. The conservation and sustainable use of local aquatic ecosystems, ponds, rivers, coastal commons by artisanal fisherfolk and smallholder farmers is important to the survival of both humans and the environment. Since aquatic organisms, including fish, provide much of our food supply as well as underpinning the income of coastal peoples, it is critical that fisherfolk and smallholder farmers have genetic reserves and sustainable ecosystems to draw upon as aquaculture and marine fisheries management continue to evolve. Ecosystem diversity Ecosystem diversity refers to the variety and variability of different components in a given geographical area (e.g. landscape, country). In the context of agrobiodiversity ecosystem diversity refers to the diversity within and between agroecosystems: e.g. pastures, ponds and rivers, planted fields, hedges, trees and so on. Landscape-level biodiversity has received less research attention than the other levels of biodiversity. Contributions of agrobiodiversity to food and agriculture Introduction Contributions from agrobiodiversity to food and agriculture are usually categorized by their contribution to ecosystem services. Ecosystem services are the services provided by well functioning ecosystems