The effects of ecosystems on disease and of disease on ecosystems

This is due to the fact that many pathogens are specific to one or a few crop species or genotypes. As a result, when susceptible genotypes of a particular species are present at higher frequency, covering a higher proportion of agricultural land, losses to disease for that species will tend to be higher. Agricultural production is dominated by extensive monocultures, which is partly due to artifacts of agricultural policy and decision-making, but also partly due to the real challenges of understanding and manipulating the ecological genomics of a single crop genotype. There are trade-offs in investing agricultural research in many versus only a few agricultural species. Agricultural diseases may emerge or re-emerge for a number of reasons, including new pathogen introductions, new adaptation of pathogens to previously effective resistance genes, and changes in the abiotic environment. Technological abilities in ecological genomics that are needed to support management of emerging and long-term disease include the ability to manipulate disease resistance genes in crops, the ability to devise crop plant communities at multiple spatial scales that are optimal for a range of agronomic traits, and the ability to manipulate microbial communities for disease suppressive characteristics. The construction of crop variety mixtures is an example of a technology that draws heavily on ecological ideas and has also contributed greatly to our understanding of disease ecology through experiments examining the effects of patterns of host variability on disease through time and space. New forms of agricultural systems, such as perennial grains, may also offer environmental benefits such as reduced erosion and nutrient leaching, but will also challenge ecological genomics to provide effective methods of disease management since pathogens may more easily accumulate in long-term agricultural stands. While agricultural systems have typically grown less diverse over the past century, advances in ecological genomics are likely to make it feasible for systems to incorporate higher levels of diversity in the future as agricultural scientists are better able to influence and manage complex agricultural communities for reduced disease. Agricultural genotypes and individuals can, in theory, be completely replaced in order to increase disease resistance, with the main ethical concern being preservation of traditional varieties. Agricultural scientists have emphasized manipulating the genetic composition of agricultural species for disease management, often trying to perfect a single crop genotype. Improving even a single crop species has, in fact, often been a substantial challenge. Ecologists have long been intrigued by the relative fitness of specialist and generalist organisms, and the question of how to partition agricultural research effort can be framed similarly: are agricultural specialists or agricultural generalists better adapted?