SPARROW LAB 2011: FIRST SUBMISSION
Group size, vigilance and foraging in Golden-crowned Sparrows
Animals vary greatly in sociality: some live solitary lives while others live in social groups. Understanding the costs and benefits of group living has been a central problem in behavioral ecology for half a century. In this lab we used time budget analysis to explore the costs and benefits of group foraging golden-crowned sparrows in the UCSC arboretum. These birds are ideal for such a study because they can be alone as well as in groups of varying size.
In theory, the costs and benefits that might change with group size include: (i) increased safety from predators in bigger groups due to the benefits of many eyes watching for predators which can translate into (ii) increased foraging time for individuals in large groups because they are able to spend less time scanning for predators. However, larger group sizes can also (iii) increase in the rate of aggressive interactions, which may or may not overwhelm the other factors. We collected time budget data on the frequency of these three different activities for individuals in different group sizes: feeding, scanning and aggression. We will analyze time budgets (proportion of time, as measured by proportion of ticks in each behavior category) in relation to group size. For this first report, we will just consider one group size (lumping total number of the two species of sparrows and the California towhee).
One difficulty we needed to deal with was ambiguous cases that were difficult to assign as feeding or scan. The way we dealt with this was to collect a fourth category of data: ”feed-scan” I have compiled all of your data, and converted counts to proportions. I did this in two ways: (1) counting feed-scans as feeds and (2) counting feed-scans as scans. You will analyze the time budgets both ways and see if you get the same answer or a different answer. This might help inform us as to whether what we call feed-scan is likely to feeding or scanning.
Your paper should address the following question: Is there evidence to support Caraco's predicted relation between group size, scanning and feeding? If you do not find evidence for the predicted pattern, provide a possible explanation. One option is to consider the ASSUMPTIONS that went into the prediction. Predictions from theory are only expected to hold if the assumptions behind the theory are true.
Key paper: Caraco, T. 1979. Time budgeting and group size: a test of theory. Ecology 60: 618-627. This paper is attached and I will also post it on the class website.
Style of report:
This is a short report (2 pages; double spaced 12 times font; you can make it as long as 3 pages of text if you feel you have to but NO LONGER THAN 3 (two really should do it for this first report). PLEASE READ THE HANDOUT WE GAVE YOU ON WRITING SCIENTIFIC MANUSCRIPTS AND FORMAT THE PAPER ACCORDINGLY. Include 5 references (i.e. cited scientific papers, including Caraco) Cite papers, not websites! We will not present graphs in this first report, but you will have the option of presenting graphs and tables in the second sparrow report. We will also collect more data and we may do additional analyses for the revised sparrow report due later.
Use WEB of Science to find references:
The Web of Science (a database search engine) is a great way to track down useful references. You can find Web of Science on the Science library home page on the web. One easy way to find good papers is to first find Caraco's paper, and then look for papers that cite it (some 250 papers). Most of these will not be useful for your report; try using the titles to guess which ones are most likely to be useful and you should actually read the papers: YOU WILL LOSE POINTS FOR CITING IRRELEVANT PAPERS!
What to analyze:
Your data have been compiled in an Excel file (named Compiled_Sparrow_Data.xls). Because we are dealing with proportions we will use a NON-PARAMETRIC test in this exercise: the Spearman Rank correlation will be used to test if group size is correlated with the different proportions we have estimated. Do this in JMP as we showed you in class. You will do five comparisons (accounting for the two different ways we counted “feed/scan”) for this report: examine the correlation between group size and each of the following: (1) proportion of time feeding, (2) proportion time scanning, (3) proportion time aggressing.
Reminder on how to do a Spearman Rank correlation in JMP:
• go to menu bar at top
• open Analyze
• within Analyze click on multivariate methods tab
• within multivariate methods tab click multivariate
• drag two variables into Y, columns box: group size and proportion aggression
• click OK
• in the analysis result that pops up, click the red tab by multivariate at the top
• go to the nonparametric correlations tab and then choose Spearman’s r
• the program then calculates the Spearman Rho statistic ( ρ ) and the P value associated with this value of the statistic
• make a note of the result or copy and paste the result table as Barry indicated in the general tutorial
• repeat this analysis for the other four proportions
Sample size is not reported here in the JMP output but you can check the data file. In this specific case, sample size is number of rows of data; same for all comparisons)
Here are a couple of examples of proper ways to report a result in the Results section (data are from a different data set so your N will differ):
IMPORTANT: HOW TO REPORT STATISTICAL RESULTS
Here are a couple of made up examples:
The proportion of an individual's time budget spent in aggressive interactions was positively correlated with group size (Rho = 0.47, N = 61, P = 0.0093).
or
The proportion of time an individual spent in aggressive interactions increased significantly with group size (Rho = 0.47, N = 61, P = 0.0093).