STUDENT INSTRUCTIONS

Background information:

      This is a data set from this paper: D. A. Arrington, K. O. Winemiller, W. F. Loftus, and S. Akin. 2002. How often do fishes 'run on empty'? Ecology 83 (8): 2145:2151.

      This study grew out of a similar one on lizards in which the proportion of animals with empty stomachs was used as an index of "instantaneous energy balance". In that study the researchers wanted to know whether lizards alternate between states of feast or famine in contrast to keeping a positive energy balance (which means they consume more energy than they use) all the time.

      Arrington et al. (2002) wanted to look at the energy balance question with animals with different feeding modes - such as ones that eat insects vs. ones that eat other animals. They used fish in their study because these animals display a wide range of trophic (feeding) specializations. They measured the number of fish with empty stomachs in a very large data set - 36,875 individual fish of 254 species collected from Africa, South America, Central America, and North America. They only included samples with >10 individuals in the study; average sample size was 145.

      The researchers examined the relationship between "trophic status" (what an animal eats) and number of fish with empty stomachs. (Since they were looking at the feast vs, famine question, they were interested in fish with empty stomachs). They classified fish into 4 categories - piscivores (carnivores that eat other fish), omnivores (eat everything), invertivores (eat invertebrate animals), and algivores/detritivores (eat algae and detritus).

      They also looked at reproductive behavior of the fish and found that within the piscivores a disproportionate number provided parental care (e.g. mouth brooding - the fish takes care of baby fish in its mouth! This certainly would limit what the fish could eat).

      Arrington et al. conclude that animals able to put surplus energy into lipids and other storages can tolerate the energy costs associated with high-cost reproduction and also survive stress periods. (Under which of the four feeding strategy would fish more likely be able to store fats? Which fish have "high-cost" feeding strategies). They state that their results "reveal a potential influence of feeding frequency and energy balance on life history evolution."


With the instructions below you will be able to make your own figure (graph) of the empty stomach/feeding strategies data.


Using the Excel file to make a simple figure:

1. Go over the Excel spreadsheet to make sure you understand the headings, the terms, and the question that the scientists were asking.

2. Next, highlight the columns from the words "Trophic Category" and Percent" down to the end of the numbers.

3. To make this bar graph figure, click on "Chart Wizard" and select Column and then Clustered Column with 3-D.

4. Label the x and y axis; increase the font size so that you can read it well. 5. After the figure appears on your sheet, widen it by using the "stretch-out" feature at the top and bottom right side of the graph; also get rid of the "series" box by clicking on it and selecting "delete".

6. Now examine the figure to interpret the data. What are your conclusions? Is there anything more you would like to know? How else could you plot these data to make a "neater" graph.