A major area of study within the impacts of global warming is range shifting. Over the remainder of the century, climate change is expected to cause many species' habitats to expand, collapse, or change (5). This is the main concern involving the impacts of climate change on Malaria, as the suitable habitat for mosquitoes is likely to increase in size due to warming and changes in precipitation. Climate change will most prominently impact the spread of Malaria by its influence on the Anopheles mosquito, which is the vector by which Malaria is passed from human to human. As shown below, Malarial transmission is highly tied to changes in temperature, implying that increasing temperatures with warming climate will cause increasing transmission rates.
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| Original Figure - using data from Alonso et. al. (2011) (1) Shows changes in temperature and Malaria cases as reported from a single hospital in Kenya and demonstrates strong relationship between changing temperature and rate of infection |
Thermal Response
Climate change is expected to differentially favor species with wide thermal windows and short generation times (7). Mosquitoes have short generation times and require a wide variety of temperatures for survival, as demonstrated by the figure below (12). This figure shows performance curves for all stages of life of the Anopheles Mosquito. For instance, the egg to adult survivorship curve (middle, right) shows at what temperatures the most eggs grow to full adulthood. Mordecei et. al. state that the synthesis of all of these performance curves gives an optimal thermal temperature of the Anopheles mosquito that is much lower than previously believed (12). Therefore, the Anopholes is expected to survive in environments that were previously believed too temperate. This will allow Malaria, via mosquitoes, to spread beyond its previous boundaries.
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| Mordecei et. al. 2012 (12) - Thermal performance curves for mosquito and parasite life-history traits |
Changes in the patterns of rainfall is another large factor contributing to the range shifting of the Anopheles. Currently, mosquitoes have high survival and reproductive rates in savannah habitats. The savannah is characterized by a distinct dry season in winter and a rainy season in the summer (9). During the dry season, rivers and streams dry up to create pools or other forms of stagnant water. Anopheles reproduce in stagnant water, so increased drought or standing water will cause an increase in the number of mosquitoes present and therefore increase malarial transmission rates (14).
Rainfall has been measured to increase, but stay seasonal. During drought months, man-made drums and cisterns are put out to hold water, which also serve as breeding ground for mosquitoes. During wet seasons, increased rainfall will develop marshlands and bogs that also provide breeding territory for the mosquitoes in the rainy seasons (14,20).
Overall,
Changes in rainfall patterns and increases in temperature are predicted to allow mosquitoes a wider range of breeding habitat. This will allow more transmission of Malaria via its mosquito vector. For instance, many highland areas in Burundi, Kenya and Uganda that have been historically classed as Malaria-free are now experiencing epidemics (2).
Another solid page. You introduced two of the topics in class by discussing thermal specialists and range shifts. The graphs were helpful and informative.
ReplyDeleteGreat use of your figures on this page in order to help explain about range shifts and thermal specialists.
ReplyDeleteRange shift and physiological responses are two of the class topics. I feel like most people missed including topics from class into their blogs. It's great that you were able to find so much information on these two topics. -Patrick
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