marine ecology lab summer 2009 please be on time please turn off cell phones please read labs before...
TRANSCRIPT
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 Ho
Refute hypothesisand model
MODELSExplanations or Theories
OBSERVATIONSPattern in Space or Time
HYPOTHESISPredictions based on model
NULL HYPOTHESISLogical Opposite to Hypothesis
EXPERIMENTCritical test of Null Hypothesis
INTERPRETATION Reject Ho
Support hypothesisand model
Components of a Research Program
Types of EvidenceNon-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 EvidenceNon-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 EvidenceNon-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 EvidenceNon-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 EvidenceNon-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 ExperimentalApproaches to Testing Hypotheses
Types of Experiments
Factors Lab Field Natural
Variable Control
Site Matching
Tracking Change
Duration
Spatial Variability
Realism
Generality
High
High
Yes
Short
Least
None/ Low
None
High
High
Yes
Short
Medium
Medium
Low
Yes
None
Low
Long
Highest
Highest
Highest
