Marine Ecology Lab Summer 2009 Please be on time Please turn off cell phones Please read labs BEFORE coming to class Do not hesitate to ask questions-you’re the customer

Retain H o Refute hypothesis and model MODELS Explanations or Theories OBSERVATIONS Pattern in Space or Time HYPOTHESIS Predictions based on model NULL HYPOTHESIS Logical Opposite to Hypothesis EXPERIMENT Critical test of Null Hypothesis INTERPRETATION Reject H o Support hypothesis and model Components of a Research Program

Types of Evidence Non-Experimental Research Sampling (Recon, pilot study, sample size placement and number) Data dredging Experimental Research Natural experiments Mensurative experiments Manipulative experiments -Pulse and press

Principles for Environmental Studies Be able to state the question you are asking concisely. Your results will be as coherent as your initial conception of the problem Take replicate samples within each combination of time, location and other controlled variable. Differences among can only be demonstrated by comparisons to differences within. Take an equal number of randomly allocated samples for each combination of controlled variables. Taking samples in “representative” or “typical” areas is not random sampling.

Principles for Environmental Studies -2 To test whether a condition has an effect, collect samples both where the condition is present and where it is absent but all else is the same. An effect can only be demonstrated by comparison with a control. Verify that your sampling method is sampling the population you think your are, with equal and adequate efficiency over the entire range of conditions to be encountered. Variation in efficiency among areas biases comparisons.

Principles for Environmental Studies-3 If the study area has large heterogeneities, break the area into homogeneous sub areas and allocate samples to each in proportion to the size of the sub area. Verify that your sample unit size is appropriate to the sizes, densities and spatial distributions of the organisms you are sampling. Then estimate the number of replicate samples required to obtain the precision you want.

Types of Evidence Non-Experimental Research Sampling (Recon, pilot study, sample size placement and number) Data dredging Experimental Research Natural experiments Mensurative experiments Manipulative experiments -Pulse and press

Data Dredging Hypotheses must be specified in advance of searching the available literature. Using only the data sets that agree with your hypothesis or that look “interesting” are biased approaches and should not be used.

Types of Evidence Non-Experimental Research Data dredging (Meta-analysis) Sampling (Recon, pilot study, sample size placement and number) Experimental Research Natural experiments Mensurative experiments Manipulative experiments -Pulse and press

A Natural Experiment

Types of Evidence Non-Experimental Research Data dredging (Meta-analysis) Sampling (Recon, pilot study, sample size placement and number) Experimental Research Natural experiments Mensurative experiments Manipulative experiments -Pulse and press

Mensurative Experiment

Types of Evidence Non-Experimental Research Data dredging (Meta-analysis) Sampling (Recon, pilot study, sample size placement and number) Experimental Research Natural experiments Mensurative experiments Manipulative experiments -Pulse and press

Manipulative Experiment

Pitfalls in Manipulative Ecological Experimentation Artifacts (cage effects)- e.g., increased larval settlement inside predator exclusion cages Pseudoreplication- occurs when replicates are not independent or when no replication exists Changes in controls- can occur due to natural variability

Trade Offs Among Experimental Approaches to Testing Hypotheses Types of Experiments Factors LabFieldNatural Variable Control Site Matching Tracking Change Duration Spatial Variability Realism Generality High Yes Short Least None/ Low None High Yes Short Medium Low Yes None Low Long Highest