TESTING THE IDEAL FREE DISTRIBUTION: FEEDING EXPIREMENTS WITH TURTLES

BY: Submerged Scales in Hiding Isabella Castillo

Emilee Aguerrebere, Shelby Weber, Jesus Contreras

and Julian Moreyra ABSTRACT

The purpose of our work was to test the theory of the Ideal Free Distribution (IFD) on turtles. We used a pond at Florida International University (FIU) and we fed turtles different amounts of food at three different feeding stations. Some of the results confirmed our hypothesis, that the turtles distribute themselves ideally among feeding stations. Unfortunately, some of our results for turtles were not useful because interference of the turtles by ducks. We also tried to combine numbers of turtles and ducks to see if the total number followed the IFD, but the data were very noisy, so the results were not clear. INTRODUCTION The topic of our research was the Ideal Free Distribution, and the objective of our study was to determine if turtles use the Ideal Free Distribution when feeding or being fed. The Ideal Free Distribution, in ecology, often occurs when animals distribute themselves among different resources like food, shelter, or water. The term “Ideal Free Distribution” contains three words. The word “Ideal” means what is best for an individual. The word “Free” means that the animals follow their own will; they can go wherever they want without being interfered with. The word “Distribution” is how the animals are arranged in space (Darling 2000, Nicanor 2007).

For example, if there is a group of six birds feeding in a field that has seeds distributed in two patches, and one patch has twice as many seeds as the other patch, how should the birds distribute themselves so that each gets the most food? According to the IFD theory, it would be expected that there would be two birds in the poor patch and four birds in the rich patch, the same proportion as the seeds. So, if one area contains more food than the other area, the animals would distribute themselves in proportion to the food. The purpose of the experiment was to see if the turtles would distribute themselves according to this theory. In this experiment the turtles were fed at three different rates, high, medium, and low. We asked if the turtles go to the station with the least food, most food, or the medium amount of food. If all the turtles go to the station with the most food, they would get less than if they distributed themselves among the three stations in proportion to the food supply. But if the turtles distribute themselves in proportion to the amount of food at the three stations, all turtles will get approximately the same amount of food and no turtle would do better by moving to another station. Our Null Hypothesis was that there would be no significant difference in the numbers of turtles feeding on stations of different amounts of food. The Alternative Hypothesis was that there would be significant differences in the numbers of turtles feeding on stations with different amounts of food.

METHODS We visited Florida International University (FIU) on June 18, 21, 23 and 30. We used two ponds at FIU for our experiments. The main pond that we used is located close to the FIU library (Figure 1). The size of the pond is about 2600 square meters or about 1 quarter of a hectare. The shore of the pond was clear of vegetation. We noticed fish and ducks, as well as turtles were in the pond. The turtles were mostly red sliders, but there were also some large Florida soft-shelled turtles.

Figure 1. Photograph of study sites, Florida International University, showing the ponds used (see arrows), where the main pond is lower and to the left of the other pond. Our materials were the following. We used a cup to hold the food that we feed the turtles. The food we used is called Koi’s Choice premium fish food. These are small pellets that turtles also like. We threw the food in the pond using three different spoons: teaspoon, table spoon, and ½ of a table spoon. The data were taken using a pen or a number 2 pencil and our steno notebook with 80 pages and from Office Max. Our undergraduate facilitator called out the time with his timer on his Motorola phone. We used the following procedure. First we were divided into three teams spaced out two meters apart each along the shore. Then food and spoons were given out to the teams. The timekeeper would say when to throw the food and when to count how many turtles there were. Every 30 seconds the timekeeper would say “throw”. We threw the food into the pond about 1 meter in front of us so the turtles could come to the food. Ten seconds after he said “throw” he said “count”. We counted how many turtles there were in front of us and wrote it in our steno notebook. We would do that for 15 minutes or less. Last but not least we come back into the computer lab and wrote the data in the Excel spread sheet. Then we made graphs and chart about the work we did. These are called “time series” of the numbers of turtles (or turtles and ducks) at each feeding station every 30 seconds.

RESULTS On the first day of our study, June 18, we started at about 9:30 a.m. and counted turtles

in the main pond at three feeding stations for three spoon sizes. There was some interference of the turtles by ducks. The number of turtles, plotted every 30 seconds, are shown in Figure 2.

Figure 2. Results of experiment on Day 1

On June 21, 2010, we went back to the same pond and took data starting at 9:38 a.m. Our group

noticed that there were already fish feeding on the pellets at 30 seconds. We noticed the ducks interfered with the feeding of the turtles, so we counted both ducks and turtles. (We also noticed that there were patches of oil, maybe from the construction they were doing across the lake.) The data are shown in Figure 3.

Figure 3. Results of experiment on Day 2

The next set of data was taken June 23, 2010. At 10:45 a.m. at the main FIU pond. Again there seemed to be patches of oil, probably from the construction site across the pond. Also the ducks interfered with the feeding of turtles so we counted both ducks and turtles. The results are shown in Figure 4.

Figure 4. Results of experiment on Day 3

These final set of data was taken on June 30, 2010. At 10:23 Am at the second FIU pond. This

pond had fewer turtles than the first one, but had no ducks to interfere with the turtles. We only started counting turtles after 400 seconds, because it took time to attract enough turtles two all three stations. The results are shown in Figure

Figure 5. Results of experiment on Day 4

DISCUSSION AND CONCLUSIONS

The purpose of the experiment was to determine if animals (turtles) followed the ideal free distribution (IFD) in their feeding. When we finished our experiment we realized there were

many problems in our experiment. The FIU pond was a great place to conduct the experiment because of all the turtles. When we conducted the experiment there were not only turtles, but also fish and ducks, which created a problem. The ducks came and were interfering by eating all the available food which was for the turtles. Basically, we tried to mislead the ducks to the other side of the pond but, they did not fall for it and they probably influenced our first experiment (Figure 2), though the results are not too unreasonable. On average, the turtles were in rough proportion to the spoon sizes. When, we tried again in the second experiment we changed the experiment to include ducks and turtles. The experiment was not too successful, because the data were very noisy (Figure 3). We tried again to get the turtles alone; we went out again and our perseverance paid off. This time we managed to frighten away most of the ducks, because we realized that if you open and close an umbrella fast it scares the ducks away and not the turtles. Our data, in Figure 4, showed some tendency for the turtles, plus a few ducks, to follow the IFD. Finally, in our last experiment, in the second pond, we managed to totally avoid ducks. In this case, although there were few turtles, they tended to follow the IFD (Figure 5).

We conclude that our hypothesis supported our data with the turtles because they had an IFD and went to different food stations roughly in proportion to the food available. With the ducks our hypothesis did not support our data because they came in just devouring all the food without really having an IFD.

Our null hypothesis was that the turtles will not have an ideal free distribution and will all just go to the biggest patch of food instead of spreading themselves. The alternative hypothesis is that the turtles will have an Ideal free distribution and even themselves out in all of the food patches. The results contradicted the null hypothesis because the turtles distributed themselves among the food patches and did not just all go to the food station with most food. Results supported the alternative hypothesis with the turtles.

AKNOWLEDGMENTS

We would like to thank Jiang Jiang, Don Deangelis, Dr.Robster, HHMI, FIU, Dana Kremples, Lee Alverez and Jen Roman. These people helped us on the journey to find the Ideal Free Distribution. Without these people our experiment would be nothing. THANK YOU! REFERENCES Nicanor Quijano. 2007. The Ideal Free Distribution: Theory and Engineering Application, IEEE Transactions on Systems, Man, and Cybernetics—Part B: Cybernetics 37:154-165. Ruth A. Darling. 2000. Habitat Quality and the Distribution of Fish: Are Fish ‘Ideal Free’? Bioscience, 26: 27-30.