Climate change consists of changing rainfall and humidity, increasing average global temperature and rising sea levels. Climate change is become a concerned issue that has direct negative effects on environment, diversity of animals and plants and humans. Furthermore, changing climate also induces indirect effects on global biodiversity by increase detrimental effect on wildlife health.
How climate changes impact on wildlife health?
Many scientific evidences support that climate changes as an environmental drivers of wildlife infectious diseases that include vector-borne diseases and emerging diseases. This phenomena have significant effects on wildlife’s health in many different ways.
According to epidemiological triangle (Figure 1) that is a model illustrates the relationship among host, agent and environmental components, climate is a part of environmental factors that has an interaction with agent or pathogen and host. Firstly, climate can influence on host susceptibility. This is due to the fact that dramatic climate change leads to extreme conditions that become stressors on wildlife, such as, thermal stress and hydric stress. Consequently, these stressors can lead to impaired immune response or immunosuppression in wildlife. These can imply that environmental stress increases the risk to acquire disease or increases susceptibility of wildlife. Although wildlife have many mechanisms to mitigate environmental stress, rapid or unpredictable stress may exceed this processes. For example, increased average temperature in northwest Minnesota, USA, resulted in declined of moose population, this is because of heat stress contributed to immunosuppression and more susceptible of moose to infectious diseases or parasites such as brain worm and liver fluke (1). In addition, severe drought in Tanzania as a consequence of climate change also has an effect on wildlife health. Researchers found that unusual mortality of elephant particularly in young male elephants is associated with this extreme climate event (2).
Secondly, climate changes have been involved to disease pattern modification by change in abundance, development and distribution of vectors and agents. Many pathogens can growth rapidly and become a main drivers of host extinction under certain conditions. As mentioned above, not only high temperature that has impacts on moose’s susceptibility but increase rainfall in Northwest, Minnesota can also lead to increase survival of snails, intermediate host of brain worm, and resulted in more exposure of moose to infected snails (1) (Figure 2).
Furthermore, climate changes have consequences on geographic range of diseases by extending the expansion range of disease or shifting the range of pathogen. Many researches on the shift of geographic range of pathogen illustrate the northward movement of pathogen’s distribution. For instance, expansion and shift of avian malaria to higher elevation in the Hawaiian Islands as a result of climate warming has threated to endangered native birds. This is because of warmer climate contributes to increase mosquito abundance due to metabolisms of mosquito are also increase with increasing temperature. As a consequence of this, feeding must be increased to maintain energy balance. Increasing in biting rate leads to increase the chance of parasite (Plasmodium relictum) transmission that cause avian malaria. In addition, reduction of the time for parasite development in vector as a result of temperature change is a key factor for more disease expansion (3). It can imply that distribution of avian malaria will increased with rising in average global temperature that can increase temperature in higher elevation.
Global biodiversity crisis?
As a consequence of climate change, infectious disease in wildlife is more severe and spread in many geographical area. Due to that fact that most pathogens can infect multiple species of host (board range host), climate warming contributes to more distribution of pathogens to naïve host populations that may be sensitive or have no resistance to these pathogens. This phenomena potentially leads to dramatic depopulation of host species.
In addition, if decline of population has been followed by chronic infection in the wildlife population, the local extinction of host species may occur. For example, chytridiomycosis that caused by Batrachochytrium dendrobatidis or chytrid fungus spread widely in European countries and become a key component of the local extinction of many amphibian species in the areas. Research in amphibians shows that increase average global temperature relates to the outbreak of this fungus, because of warming temperature increase chytrid growth on the amphibian species (4). In addition, increasing temperature has an effect on amphibians’ immune response to chytrid fungus. Some sensitive amphibian species such as Common midwife toad and Fire salamander have been suffered from chytrid fungus infection and contributed to dramatic decrease in local population (Figure 3).
In conclusion, rapid climate changes has an indirect impact on global biodiversity by influencing on wildlife health in individual and population levels. Climate changes have altered interaction among host, pathogen and vector and have a negative effect on host susceptibility by increase risk to acquire the disease. Moreover, change in distribution and dynamic of disease are also as a consequence of climate change. These mechanisms lead to decrease in population of wildlife across many landscape and then can allow wildlife species to become extinct!
- Murray, D. L., Cox, E. W., Ballard, W. B., Whitlaw, H. A., Lenarz, M. S., Custer, T. W., Barnett, T., and Fuller, T. K. (2009). Pathogens, nutritional deficiency, and climate influences on a declining moose population. Wildlife Monographs, 166, pp.1–30.
- Foley, c., Pettorelli, N., and Foley, L. (2008). Severe drought and calf survival in elephants. Biology letters, 4(5), pp.541-544.
- LaPointe, D. A., Atkinson, C. T., and Samuel, M. D. (2012). Ecology of Avian Malaria. Annual of the New York of Academy of Science, 1249, pp.211-226.
- Mitchell, K. M. Churcher, T. S. Garner T. W. J., Fisher, M. C., et al. (2008). Persistence of the emerging pathogen Batrachochytrium dendrobatidis outside the amphibian host greatly increases the probability of host extinction. Proceeding of the Royal Society B-Biological Sciences, 275, pp.329-334.