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Chapter 1

Ecology - chapter 1

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Western University
Biology 2483A
Hugh Henry

Chapter 1 – The Web of Life Case Study: Deformity and Decline in Amphibian Populations  Worldwide, the frequency of amphibian deformities was rising, and the global amphibian populations were declining.  Researchers were worried about amphibians declining for three reasons  The decline appeared to have started recently across wide regions of the world.  Some of the populations in devline were located in protected or pristine regions far from the effects of human activities.  Many scientists view amphibians as good “biological indicators” of environmental conditions for a number of its characteristics:  Permeable skin with no hair/scales/feathers protecting them, and their eggs also lacked protection.  Spends most of their life in the water and partly on land therefore exposed to a wide range of threats such as pollution, changes in temperature, and amount of UV.  Many do not move from their birthplace, therefore a decline in the population indicates the deterioration of the environment. Introduction: Humans have such a large influence on the planet on both land and oceans leading effects such as global climate change, decline in fish stock, “dead zones” in the ocean etc. But we are also part of the environment and we are beginning to realize that we need to understand nature and its systems, hence understand ecology. Connections in Nature  The events in the natural world can be linked or connected to one another, as the organisms interact with one another/with the environment.  They don’t have to directly interact but by sharing an environment they are indirectly interacting with each other. Early observations suggest that parasites cause amphibian deformities  A researcher, Ruth, hypothesized that a parasite (Ribeiroia ondatrae) caused the deformity.  Implanting a glass bead in a developing tadpole by the not yet grown limbs tested the hypothesis.  They reported that the beads caused deformity similar to those found in amphibians with parasites. A laboratory experiment tests the role of parasites  At first when the deformities were found in the amphibians, Ruth believed that they were an isolated local phenomenon.  Although Ruth and others provided indirect evidence of the parasite causing deformities, another researcher, Johnson, set out to provide a more direct test of the hypothesis.  Johnson and other researchers focused on two of the four ponds where they found deformed frogs, and thought that the deformities were caused by pollutants (ex pesticides, and heavy metal) but they were not found in the ponds.  The four ponds they focused on were the only ponds with the frogs and an aquatic snail which was a host required for the Ribeiroia parasite to complete its life cycle and produce offsprings. The dissection of the frogs from these four ponds also contained Ribeiroia cysts.  This again was only indirect evidence; hence an experiment was carried out, where tadpoles from ponds that was not known to have any deformities were put in containers with different amounts of parasites.  Johnson found that as the number of parasites increased fewer tadpoles survived, and the majority of the ones that did survive were deformed. So this supported the hypothesis and also suggested that the parasites could contribute to amphibian declines. A field experiment suggests that multiple factors influence deformities  Kiesecker conducted a field experiment in six ponds that all had Ribeiroia and only three with pesticides like a farm to examine the possible joint effects of parasites and pesticides.  In each pond six cages were put in that contained tadpoles, three of where parasites could pass through, and the other three that could not. Tadpoles couldn’t escape.  The results showed the frogs raised without the parasites had no deformities regardless of whether the lake had pesticides or not. Deformity was found in frogs that were exposed to Ribeiroia. But there was a higher percentage of deformities in the frogs that were in the lake with pesticides.  Kiesecker hypothesized that pesticides may decrease the ability of frogs to resist infection by parasites. This hypothesis was tested in a lab exposing all tadpoles to Ribeiroia and half with pesticides and half without. The results suggest that pesticide exposure may affect the frequency with which parasites cause deformities. Connections in nature can lead to unanticipated side effects  Although we know that the parasites cause deformities why has the frequency of the deformity increased so much compared to the past?  increase in pesticides  Pesticides decrease the ability of amphibians to protect themselves from parasite attacks.  Other environmental changes such as addition of nutrients to natural/artificial ponds can lead to increase in parasites, algae formation lead to an increase in snail population which are hosts to parasites hence increase in deformity. We live in an ecological world  When people alter one aspect of the environment, we change another aspect even if it is not intended.  Changes in our environment not only leads to deformity in amphibians but also risks human health. Ex) spread of may diseases.  No matter how far we are from the natural world in our every day lives, we are part of an interconnected web of life. Ecology  Ecology = the sc
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