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KEYWORDS FOR DATASET: Insect, Biology, Foraging
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ACCOMPANYING DATA PROVIDED BY: Peter Nonacs, PhD
                               UCLA, Department of OBEE
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GENERAL EXPLANATION OF THE STUDY
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The two accompanying data files are from a study on the foraging habits
of two species of ants: thatch ants (Formica planipilis) and seed 
harvester ants (Pogonomyrmex salinus). The study was concerned
with the ant colonies' different "strategies" for optimizing the balance 
between collecting food and exposure to risk. The idea, in its simplest
form, is that sending more ants to look for food farther away from the 
colony is more likely to increase the colony's food supply; traveling 
away from the colony, however, exposes ants to the risk of death by 
starvation and predation. Natural selection suggests that colonies will
develop foraging strategies that maximize the colony's net gain, defined as
how much the colony grows--this depends primarily on its food supply--minus 
how many ants die. A variety of different maximizing strategies exist, and
different species often have different strategies. Some colonies develop
"worker-conservative" foraging strategies, in which ants foraging at 
greater distances consume relatively more food: this minimizes the risk of
starvation and leads to fewer deaths. Other colonies use strategies that
conserve energy (the colonies overall supply of food). In this case long
distance foragers, who are more likely to die, will consume less food so
that their deaths will not be as much of a strain on the colony's food 
supply. 

More specifically, this study investigated the relationship between the 
size of the ants and the distance at which they foraged. Other studies have 
shown that larger ants use energy more efficiently than smaller ones, and 
this suggests that larger ants would be more likely to forage at greater 
distances. Thus ants were collected at various distances from the colony, 
weighed, and measured. Because an ant's weight provides a measure 
of how much food, or energy, it carries, and because headwidth measurements 
allow the ants to be classified by size, the data provides detailed 
information on the correlations among ant size, foraging distance, and 
energy supply. This information, in turn, gives insight into foraging 
strategies: we can, for example, determine whether a colony's strategy is
"worker-conservative" or "energy-conservative," or a more complex 
combination of the two. We might find, for example--by analyzing the 
relationships among size, foraging distance, and energy supply both for the
colony as a whole and within the separate size classes--that a colony's 
overall strategy is "worker-conservative," but that within size classes the
strategy is "energy-conservative." These analyses, finally, illuminate the 
colony's survival strategies and provide evidence for or against competing 
evolutionary theories. 

This study has not yet been published (11/29/99). 
    
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BRIEF DESCRIPTION OF THE DATA          
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The data for both files was collected at the Sierra Nevada Aquatic 
Research Laboratory (SNARL) in the Great Basin Desert Province. Collection 
trays were placed into the ground at different distances from the entrance 
to the ant colonies' mounds, and any ants walking into them were trapped. 
Thus the data may be considered as random samples of ants at various 
distances. 

The data on the thatch ants contains a total of 1199 samples, taken from a 
total of 11 different colonies. 

The data on the seed harvester ants contains a total of 577 samples, taken 
from 8 different colonies. 

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HOW TO USE THE DATA FILES
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The actual data files are comma delimited text files. The first rows contain
the abbreviations for the information recorded for each sample. The 
remaining rows each represent a single ant's corresponding information. 

There are five variables in both files. The variables are the same in both
files, although the values they may assume are not always the same. 
Here is a brief explanation of each one:
 

COLONY: ............This is a number or letter that identifies which colony
                    the sample was taken from. It is important only for 
                    distinguishing between ants from the same colony and ants 
                    from different colonies. 

DISTANCE: ..........Tells how far from the mound's entrance the sample
		    was taken. Given in meters. 

MASS or WT. (MG): ..How much the sample weighed in milligrams. This 
		    variable is used as a measure of how much food
		    (energy) each sample had. 

HEADWIDTH: .........A measure of the sample's maximum headwidth. The units
                    here are basically arbitrary, and correspond to ruled
                    increments that can be seen in the microscope with which
                    the sample is measured. Headwidth is a good indicator 
                    of an ant's size, and can be used to classify the ants 
                    by size.    

HEADWIDTH (MM): ....Same as "headwidth," only given in millimeters. 

WORKER CLASS: ......A size classification. In the thatch ant data there are 
                    five possible classes: "<30", "30-34", "35-39", "40-43", 
                    and ">43". In the seed harvester data there are four size
		    classes: "<37", "37-38", "39-40", and ">40". 

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STATISTICAL TESTS AND ANALYSES USED IN THE STUDY
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1) ANOVA (two-way layout)
2) Scheffe-S post hoc test
3) Residuals analysis
4) Linear Regression
5) One sample t-test



Go To Raw Data: 
Thatch Ant 
Seed Harvester Ant 
Download the Stata File: 
Thatch Ant 
Seed Harvester Ant 
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