International Day for Biological Diversity is being observed on Thursday to raise awareness of the importance of biodiversity at a time when over 60 per cent of ecosystem services were being degraded as a result of human activity. One of the most important challenges facing mankind today is to feed a growing population in an increasingly urbanised world confronted with the combined impacts of climate change and the unprecedented loss of biodiversity. During the past 50 years, humans have altered ecosystems more rapidly and extensively than in any other period in human history. Indeed, more land was converted to cropland during the last 50 years than in the previous two centuries. These transformations have an impact on ecosystems and the ecosystem services upon which all life relies, according to United Nations. This year's theme on "Biodiversity and Agriculture' highlights the importance of sustainable agriculture not only to preserve biodiversity, but also to feed the world, maintain sustainable agricultural livelihoods and enhance human well- being in the twenty-first century. According to the FAO, about 7,000 species of plants have been cultivated since humans first began farming. However, today, only 30 crops provide an estimated 90 per cent of the world population's dietary energy requirements, with wheat, rice and maize alone providing about half the dietary energy consumed globally. Of the estimated 15,000 species of mammals and birds, only some 30 to 40 have been domesticated for food production and less than 14 species