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Ecology Final Exam Notes

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Western University
Biology 2483A
Hugh Henry

o Six cages in each pond, three with mesh size that allowed parasite to enter  Hypothesis: pesticides decrease the ability of frogs to resist infection by parasites  Another lab experiment: Tadpoles reared in presence of pesticides had fewer white blood cells (indicating a suppressed immune system) and a higher rate of Ribeiroia cyst formation  Studies have suggested that a range of factors may be responsible for amphibian declines  The relative importance of factors such as habitat loss, parasites, pollution, UV exposure, and others are still being investigated  Synthetic pesticide use began in 1930s; use has increased dramatically.  Amphibian exposure to pesticides has also increased  Any action (increased use of pesticides) can have unanticipated side effects (more frequent deformities in amphibians)  Interaction – non-additive effect – difference between ponds with and without pesticides  Not a fully controlled experiment, so link between pesticide and deformation is not strong  Fertilizer use may also be a factor: o Fertilizer in runoff to ponds increases algal growth o Snails that harbor Ribeiroia parasites eat algae o Greater numbers of snails result in greater numbers of Ribeiroia parasites  Skerrat et al. (2007) argued that some declines may be due to pathogens such as a chytrid fungus that causes a lethal skin disease, and has spread rapidly in recent years  But climate change and altered conditions may be favoring growth and transmission of disease organisms  Hatch and Blaustein (2003) studied the effects of UV light and nitrate on Pacific tree frog tadpoles o At high elevation sites, neither factor alone had any affect. But together, the two factors reduced tadpole survival o At low elevation sites, this effect was not seen  Stuart et al. (2004) analyzed studies on 435 species: o Habitat loss was the primary cause for 183 species; overexploitation for 50 species o The cause for the remaining 207 species was poorly understood LECTURE 2: THE PHYSICAL ENVIRONMENT Case Study: Salmon Decline  Potential causes of salmon declines in the North Pacific Ocean: o Dam construction o Sediment from logging operations o Water pollution o Overharvesting  But the conditions of oceans, where salmon spend most time as adults, have also been implicated.
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