Browsing by Author "Moulton, Timothy P."

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    Epidemic malaria dynamics in Ethiopia: the role of self-limiting, poverty, HIV, climate change and human population growth
    (2022) Krsulovic, Felipe Augusto; Moulton, Timothy P.; Lima Arce, Mauricio; Jaksic Andrade, Fabián; Pontificia Universidad Católica de Chile. Facultad de Ciencias Biológicas; Center of Applied Ecology and Sustainability (CAPES)
    Background: During the last two decades, researchers have suggested that the changes of malaria cases in African highlands were driven by climate change. Recently, a study claimed that the malaria cases (Plasmodium falciparum) in Oromia (Ethiopia) were related to minimum temperature. Critics highlighted that other variables could be involved in the dynamics of the malaria. The literature mentions that beyond climate change, trends in malaria cases could be involved with HIV, human population size, poverty, investments in health control programmes, among others. Methods: Population ecologists have developed a simple framework, which helps to explore the contributions of endogenous (density-dependent) and exogenous processes on population dynamics. Both processes may operate to determine the dynamic behaviour of a particular population through time. Briefly, density-dependent (endogenous process) occurs when the per capita population growth rate (R) is determined by the previous population size. An exogenous process occurs when some variable affects another but is not affected by the changes it causes. This study explores the dynamics of malaria cases (Plasmodium falciparum and Plasmodium vivax) in Oromia region in Ethiopia and explores the interaction between minimum temperature, HIV, poverty, human population size and social instability. Results: The results support that malaria dynamics showed signs of a negative endogenous process between R and malaria infectious class, and a weak evidence to support the climate change hypothesis. Conclusion: Poverty, HIV, population size could interact to force malaria models parameters explaining the dynamics malaria observed at Ethiopia from 1985 to 2007.
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    High importance of autochthonous basal food source for the food web of a Brazilian tropical stream regardless of shading
    (2016) Neres-Lima, Vinicius; Brito, Ernesto F.; Krsulovic, Felipe A. M.; Detweiler, Angela M.; Hershey, Anne E.; Moulton, Timothy P.
    According to the prevalent paradigm, the major source of carbon and energy for food webs of small forested streams in temperate regions is allochthonous material from the surrounding forest. Tropical streams have not been as well studied and there has been some speculation that their food webs are more aligned with in-stream, algal production (autochthonous carbon). We studied food sources and consumers in four sites in a coastal tropical stream with gradients of 36-254m elevation, 8-73% canopy cover and 11.9-7.1km(2) watershed area, with the expectation that the food web would incorporate proportionately more allochthonous material as shading increased with smaller stream size. We analysed stable isotope ratios of carbon and nitrogen in basal resources and fauna and compared the values of consumers to the potential sources using a mixing model to estimate the proportion of allochthonous and autochthonous material in their diets. The predominant source of carbon in the food web was from algal production at all sites. There was no distinct increase in the proportion of allochthonous contribution to the diets of primary consumers and predators with increasing shading, and they did not generally change their diet with shading. Thus the food web was based more on autochthonous resources than would be expected from the paradigm for temperate streams.
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    Patterns of periphyton chlorophyll and dry mass in a neotropical stream: a cheap and rapid analysis using a hand-held fluorometer
    (2009) Moulton, Timothy P.; Souza, Marcelo L.; Walter, Taldi L.; Krsulovic, Felipe A. M.
    Periphyton distribution is affected by various physical, chemical and biological factors at different scales. In the present study, a cheap and rapid method of measurement was used to obtain the many samples necessary for spatial analysis of periphyton along an altitudinal gradient in a low-order stream in south-east Brazilian Atlantic rainforest. Fluorescence and turbidity were measured using a hand-held fluorometer and calibrated to the chlorophyll and dry mass of periphyton. Periphyton on the horizontal and vertical surfaces of different boulders was examined and shading and water current were measured as covariables. The three upstream sites with higher abundances of potentially grazing and bioturbing shrimps and mayflies had significantly less periphyton dry mass than the three downstream sites. Chlorophyll was positively related to water current, but not to shading. Variabilities in the dry mass and chlorophyll among boulders within sites were not associated with the distribution of shrimps and mayflies. The in vivo measurement was cheap, rapid, sensitive and reasonably precise compared with standard methods. The necessary sacrifice of detail of pigments (different chlorophylls and pheophytin) and dry mass (organic and inorganic constituents) and probably precision was compensated for by the insights gained from the ability to obtain a large number of samples in a hierarchical design.