BIOL 4240Field Ecology

Data, data everywhere

“Modern science proceeds by conjecture and refutation, by hypothesis and test, by ideas and data, and it also proceeds by obtaining

good descriptions of ecological events”.

Krebs 1999 p.1

• What data should be collected?

• What is useful and useless?

Data, data everywhere

• Krebs rules…1. Not everything that CAN be measured SHOULD be

measured

2. Find a problem and state your objectives clearly

3. Collect data that will achieve your objectives and make a statistician happy.

4. Some ecological questions are impossible to answer at the present time

Data, data everywhere

• Hierarchical review…

•Biosphere

•Region

•Landscape

•Ecosystem

•Community

•Population

•Individual (organism)

http://antwrp.gsfc.nasa.gov/apod/ap971026.html

http://www.mdafederal.com/geocover/geocoverortho/

gcorthoregional/africa_mosaic.jpg/viewhttp://en.wikipedia.org/wiki/Lake_Malawi

http://www.vagabonding.com/gallery_app/view_photo.php

?set_albumName=malawi&id=DSC01998_lake_malawi_fish

http://www.lazyjames.co.uk/hotrock/malawi.html

http://www.deepseaworld.com/attractions/lake_malawi.asp?css=1

Many ecological questions involve populations…

¿What are the 3 populations that exist?

Controlled vs. uncontrolled events…

¿What is the difference between spatial and temporal scales/studies?

Intervention analysis…

Year

% N

est s

ucce

ss

Other scales of measurement…

¿What is the difference between …

*Nominal

*Ranking

*Interval and ratio

scales?

Continuous OR Discrete…

¿What is the difference?

Continuous-ly worrying about precision and accuracy…

¿What is the difference?

¿How does implied precision vary?

SVL in mm for Idaho Giant Salamanders7373.473.47

Identify the following types of data

• Month when hibernation begins• Mass of salamanders• Number of salamanders > 50mm svl• Temperature of stream water

¿How many significant figures should you measure?

Sokal and Rohlf’s method1) Determine range of your data2) Range/30 AND Range/300

OR

Barford’s method

The rule of 300

5. With continuous data, save time and money by deciding on the number of significant figures needed in the data BEFORE you start an experiment

More of Kreb’s rules

When conducting calculations… your answer is only as good as your weakest link.

¿What is meant by this?

To Describe or to Infer that is the question…

¿What are the limits of inference?

At least 3 problems related to inference…1)Statistical populations2)Confounding/hidden variables3)Bias

Δ Read a sample abstract and then determine the limit of inference…

6. Never report an ecological estimate without some measure of its possible error

More of Kreb’s rules

¿ Black and white… or shades of gray?

The value of a p value…

¡Be sure you know the difference between statistical and biological significance!

7. Be skeptical about the results of statistical tests of significance.

8. Never confuse statistical and biological significance

More of Kreb’s rules

Evaluate the statement “Null hypotheses are irrelevant to ecologists”

9. Make a data form and enter your data into a spreadsheet/database

10. Garbage in, garbage out

More of Kreb’s rules

¿What can you do to minimize “garbage”?