Host diversity, vector diversity, as well as pathogen diversity, play a quintessential role in determining the biodiversity of disease ecology and the dynamic of disease. Animals, crops, and humans are adversely influenced by the presence of disease and its impact on the population, which can trigger the extinction of hosts thereby initiating evolution. Disease ecology entails the “ecological study of host-pathogen interactions within the context of their environment and evolution, has grown out of this awareness of the pervasive role of pathogens in ecosystems” (Altizer & Kilpatrick 55). The framework underlying the ecology of disease signifies understanding the transmission of pathogens and its impact on hosts and vectors as it relates to disease control.
Host diversity controls the risk of dynamic diseases within complex communities. Disease is considered a pathogenic condition of a host; however, disease is not transmitted from one host to another host instead the pathogen that causes the disease is transmitted from host to host (Holt et al. 487). Hosts typically transmit pathogens via air, soil, surfaces, or water. Hence, the combination of ecology and evolution exemplifies pathogenic change as they move from host to host. As pathogens are transmitted from one host to another host, environmental factors and evolution tend to alter conditions within the host as demonstrated in Daphnia (freshwater crustaceans) (Holt et al. 487). Analysis of the host species tends to “decrease host stress, which could increase the efficacy of immune response” thereby resulting in a diminished probability of transmission (Holt et al. 487). Research studies have shown that host diversity affects the rate of pathogenic infection.
A vector born disease system entails the transmission of a pathogen from one host to another host by a vector. Vectors are quite diverse and could include an aphid, flea, mite, mosquito, or a tick that transmits Lyme Disease (Holt et al. 489). The disease dynamic consists of two constituents including “the loading of the pathogen onto the vector, and the loading of the pathogen from vector to host” (Holt et al. 489). Encounter reduction decreased the transmission of pathogens due to the reduction of contact between the vector and host in addition to its effect on vector behavior (Holt et al. 490). If an added species serves as a host for a vector species but not the pathogen, the presence of the vectors will not accompany the host thereby decreasing pathogen transmission. A study of livestock near a human dwelling reveals the diminishing of mosquito meals (Holt et al. 490). Now that more mosquitos are deflected from the human dwelling the possibility of disease transmission from malarial mosquitos due to a reduction in contact with malarial mosquitos.
The diversity of pathogens significantly impacts host populations. The impact of pathogens is affected by the virulence of the pathogen in addition to the reduction of fitness within the host. Host fitness is measured in accordance with reproduction and survival (Altizer & Kilpatrick 55). Although pathogens with a low host survival rate due to “intermediate virulence tend to have the largest negative impacts on host populations,” host populations that are affected by pathogens of high virulence die rather quickly so the infectious period of transmission is drastically shortened (Altizer & Kilpatrick 55). Moreover, pathogens that decrease the rate of fecundity tend to have a larger impact on the size of host populations as compared to pathogens that reduce survival rates.
Pathogens with density-dependent transmission can potentially reduce host populations to a lower density as long as the rate of mortality is higher than the value attributed to the loss of immunity, recovery, reproduction, and survival rate of the host. According to a theory based on density-dependent specialist pathogens which tend to infect only one host, density-dependent specialist pathogens will seldom be able to initiate host extinction. However, pathogens that demonstrate frequency-dependent transmission, a long period of infection, or are comprised of multi-host pathogens that are transmitted from reservoir hosts to target species increase the incidence of host extinctions (Altizer & Kilpatrick 55). The genetic diversity of pathogens is directly affected by the hosts’ resistance to pathogens which are demonstrated through trade-offs between resistance traits, the evolution of pathogens to help counter traits that are resistance, as well as trade-offs targeting strain variations (Rohani & Wearing 11803). From an ecological perspective, the diversity of pathogens profoundly influences the reproductive rate and survivability of a population.
Based on the ecology and epidemiology of dynamic disease, disease risk is analyzed. An examination of the density and prevalence of disease in reservoir hosts and infected vectors is analyzed in accordance to host diversity, vector diversity, and pathogen diversity. An ecological approach to biodiversity within our ecosystem enables the utilization, provision, and restoration of resources and limits the dynamics of disease. Over time, scientific studies have enabled researchers to better understand the reason why certain species experienced drastic declines within their population. Biodiversity is accountable for the risk of disease. Contrarily, the loss of biodiversity yields an increase in the risk of disease. It is therefore important to incorporate biodiversity into the study of infectious disease. Although our ecosystem is a portrayal of ecology and biodiversity, the management and sustainability of biodiversity continue to present an ongoing challenge. In a dire effort to maintain biodiversity, it is imperative to create a paradigm shift geared toward minimizing the incidence of disease within a given species and their population.
Altizer, S., & Kilpatrick, A. M. “Disease Ecology.” Nature Education Knowledge 3(10): 55. (2012). Retrieved on March 10, 2014, from http://www.nature.com/scitable/knowledge/ library/disease-ecology-15947677
Holt, R. D., Keesing, F., & Ostfeld R. S. “Effects of Species Diversity on Disease Risk.” Ecology Letters, vol. 9, pp. 485-498. (2006). Retrieved on March 10, 2014, from http://www.caryinstitute. org/sites/default/files/public/reprints/Keesing_Holt_Ostfeld_2006_ecology_Letters.pdf
Rohani, P. & Wearing, H. J. 2006. “Ecological and Immunological Determinants of Dengue Epidemics.” PNAS, vol. 103, pp. 11802-11807.
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