Observational and Experimental Studies

Experimental Studies v. Observational Studies In experimental studies, a treatment (the independent variable) is applied. In observational studies, you do not have influence over the independent variables. Experimental studies are preferred but it is often not feasible to experiment. e.g. cannot exchange giraffe’s necks with other animal Behavior is hard to experiment because the experiment often alters natural behavior.

Zonosemata: a fly genus (group of species) Observations? Questions?

Zonosemata: a fly genus with distinct wing markings, as well as wing-waving behavior. Distinct dark bands on wings Holds wings up and waves them Display seems to mimic threat display of jumping spiders Hypotheses?

Experimental Study: to find the function of wing markings and wavings of Zonosemata Scientific Question: Do wing markings and waving behavior of Zonosemata mimic threat displays of jumping spiders and deter predation? Possible hypotheses: Flies do not mimic jumping spiders Display may instead be used in courtship Flies mimic jumping spiders to deter non-spider predators Flies mimic jumping spiders to deter jumping spiders Experimental procedure Created five experimental groups to test hypotheses

Experiment (Test): Created five experimental groups to test hypotheses

Predictions: Expectations for each trial relating to each hypothesis.

Data (Results): Other predators (anole lizards) killed and ate all the test fly types equally. Clipping and gluing did not affect flying or displaying

Analysis and Conclusion: Results consistent with hypothesis 3, but not 1 or 2 Support for hypothesis that Zonosemata deters its predators by acting like one. Important experimental design Testing control groups All treatments handled identically Randomization of order of treatments Replication of treatments Study was successful because many variables were tested, but each was tested independently.

Question: Background Research: Do snakes make adaptive choices of where to sleep at night? Ray Huey implanted garter snakes with thermo-radio transmitters Background Research: Preferred body temperature of garter snakes is 28– 32°C They move to keep body temperature near preferred during day and night Exposed to the sun or under rocks/ground

Data Observations:

Observational Study Night Retreats of Garter Snakes Experimental Question/Problem: How do garter snakes choose good retreats at night? Hypothesis: Garter snakes make retreat decisions based on the thickness of the rocks Background Research: Thickness of rock determines microhabitat temperature Thin rocks heat a lot during day and cool a lot during night Thick rocks heat and cool slowly Medium rocks heat and cool just enough

Observational Study Night Retreats of Garter Snakes Experimental Procedure: Huey placed snake models under rocks of different thickness (thick, medium, thin) and in burrows Tested temperature fluctuations at the sites Data Analysis: Found that snakes choose medium rocks to heat and cool near their preferred temperature range Conclusion: Garter snakes retreating under rocks at night show a strong preference for rocks of medium thickness