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Announcements – IB 105 26 January 2011 Discussion sections started this week! Please register iClickers using your NetID www.iclicker.com/
What is environmental science? Environmental Science – An interdisciplinary area of study that includes applied and theoretical aspects of human impact on the world Environment – everything that affects an organism in its lifetime Ecology – the study of the interrelationship between organisms and their environment Env. Science Ecology
Basic Scientific Principles Lecture Objectives: 2. Discuss how to form and test hypotheses. 1. Outline the scientific method.
Learn the differences between a scientific hypothesis, theory and law.
4. Understand the limitations of science.
Scientific Thinking Science — A process used to solve problems or develop an understanding of nature that involves testing possible answers. Scientific Method — Gaining information about the world by forming possible solutions to questions, followed by rigorous testing to determine if the proposed solutions are valid.
Specific causes for observed events.
Causes can be identified.
General rules can describe observations.
Repeated events have same cause.
Perceptions are not individualistic.
Fundamental rules of nature are universal.
Question — Usually a “what”, “how” or “why” question about the cause of the event. Observation — recording of an event that could be made by anyone with the proper equipment.
be testable and falsifiable A good hypothesis will: take into account all known facts be as simple as possible Hypothesis — Logical statement that potentially explains an event, or answers a question. Blaustein and Johnson 2003
Types of experiments: - Observational experiment - Manipulative experiment
Devise an experiment.
Predict the outcome of the experiment if the hypothesis is correct .
Manipulative experiment — experimental factors are varied to test hypothesis. Observational experiment — subjects are observed to test the hypothesis. Replication — Need to take multiple measurements.
Control – Separate variables and divide experiment into experimental and control groups. One difference between the experimental and control groups. Important features of manipulative experiments: Replication — Experiment is repeated to eliminate unconscious bias or a spurious correlation.
Conclusion — statement if the hypothesis has been supported or not by the results of the test. Scientific Method Hypotheses are never “proven” to be true!! If results match predictions, then hypothesis supported. If results do not match predictions, then hypothesis not supported.
Development of Theories and Laws Theory — A widely accepted, plausible generalization about fundamental scientific concepts that explain why things happen. Law — A uniform or constant fact of nature that describes what happens in nature. Hypothesis — Logical statement that potentially explains an event, or answers a question.
Statistics A branch of applied mathematics concerned with the collection and interpretation of quantitative data.
Probability The likelihood that a situation, condition or event will occur. How likely is it that your results are true? http://www.uregina.ca/drought
Our ability to accept or reject a hypothesis will be based on the accuracy and precision of our measurements. Accuracy - an estimate of nearness to the true value Precision - the repeatability or reproducibility of a measurement
Scientific Method Observation — Amphibian deformities are increasing world-wide Deformities in Pennsylvania wood frogs Deformed American toads What is the question? Kiesecker, J. M. 2002. Proc. National Academy of Sciences 99:9900-9904
Hypothesis 3 : The deformities are caused by a naturally occurring parasite (a disease) 3 main hypotheses: Hypothesis 2 : The deformities are caused by some chemical contaminant in the environment Hypothesis 1 : The deformities are caused by increased UV radiation
Types of Experiments: Laboratory Field Pro: Highly controlled Con: Limited reality Pro: Highly realistic Con: Many uncontrolled factors
Hypothesis 1: The deformities are caused by increased UV radiation Prediction: If deformities are caused by UV radiation, then amphibians grown in a high UV environment will have more deformities than amphibians grown in a low UV environment.
Experimental test of prediction: In the lab or field, expose one group of amphibians to high levels of UV radiation, grow the other others under normal light. Record deformities. Remember to replicate!! High UV Low UV
Results : Amphibians exposed to high levels of UV developed several types of deformities. Conclusions : High levels of UV are capable of causing deformities in amphibians Problems : Several lab tests used UV levels that were much higher than natural levels. The types of deformities were different than those found in nature.
Hypothesis 2: The deformities are caused by a chemical contaminant in the environment Prediction : If deformities are caused by a chemical in the environment, then amphibians exposed to the chemical will have more deformities than amphibians grown without the chemical.
Experimental test of prediction: In the lab or field, expose one group of amphibians to high levels of chemicals, grow the other without. Record deformities. + Chemical - Chemical
Results : Some chemicals resulted in malformations, others did not. Conclusions : Some chemicals may be responsible for some deformities in some amphibians. Problems : Hypothesis is too vague. Too difficult to isolate particular chemicals in nature.
Field survey showed no strong connection between pesticide contamination and amphibian deformities
http://berkeley.edu/news/media/releases/2002/04/15_frogs.html Popular weed killer demasculinizes frogs, disrupts their sexual development. 04 April 2002 Allowable levels of atrazine in drinking water stand today at 3 parts per billion (ppb). Hayes found hermaphroditism in frogs at levels as low as 0.1 ppb. Even with today's limits, levels of 40 ppb atrazine have been measured in rain and spring water in parts of the Midwest, while atrazine in agricultural runoff can be present at several parts per million.
Trematode cercariae , the infective stage that would attack frogs Hypothesis 3: The deformities are caused by a naturally occurring parasite (a disease) Predictions: If deformities are caused by a parasite, then amphibians grown with the parasite will have more deformities than amphibians grown without the parasite.
Experimental test of predictions: In the lab and field, expose one group of amphibians to parasites, grow the other without. Record deformities. Remember replication!! Results : Malformations were more common in the group exposed to the parasite.
ALSO: Field surveys indicate a correlation between infection and abnormalities Conclusions : Parasites are likely an important and widespread cause of amphibian abnormalities Problems : Deformities have been observed where this parasite doesn ’t occur
Does chemical exposure interact with parasite exposure? Percentage of deformities in adult frogs: Pond Parasite No Parasite 1 23% 0% 2 34% 0% 3 27% 0% 4 3% 0% 5 7% 0% 6 4% 0% Conclusion: The combination of parasites and chemicals increases the development of deformities Chemicals No Chemicals
Why do pesticide chemicals increase occurrence of developmental deformities when tadpoles exposed to parasites? Hypothesis : chemicals weaken the immune system and the tadpole ’s ability to fight off infection. Results : for 3 chemical treatments, tadpoles had higher levels of infection and lower numbers of leukocytes in blood.
Environmental issues are often complicated
No one factor explains all deformities in all amphibians
Chemicals and UV may be contributing to the overall increase in abnormalities, by allowing infection to occur more easily
Research on this issue continues
Parasites are likely a major cause of malformations
Limitations of Science
Restricted to those things that can be logically tested and falsified.
Often, multiple hypotheses can explain the observed results.
Results can be interpreted in different ways, leading to different conclusions.
- Hypotheses constantly being reevaluated and modified as more results and information are gained.
By the end of this lecture you should be able to:
Define “science” and list the assumptions it has.
Apply the Scientific Method to a sample problem.
Recognize the features of a good hypothesis and a controlled manipulative experiment.
Explain why hypotheses are never proven to be true.
Distinguish between a scientific theory, law and hypothesis.
Discuss the limitations of science.
Define statistics and explain why they are important.
Practice exam question
True or False: When designing a manipulative experiment, there should be at least two differences between your experimental and control groups.
Question comes from #3 on list. “Recognize the features of a good hypothesis and a controlled manipulative experiment”.