Testing Ideal Free Distribution in Animals & Humans. By: The Majestic Jaguars

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1 Testing Ideal Free Distribution in Animals & Humans By: The Majestic Jaguars Natalie Borrego Glenda Fernandez Genevieve Macia Victoria Marin Jordan Powell Shayla Wells ABSTRACT Ideal Free Distribution Theory predicts that organisms will distribute themselves between food sources in such a way that would maximize each individual s intake of food. We conducted a series of experiments at several locations in Dade County to verify the validity of this theory. At each location either two or four stations were randomly established with varying amounts of food sources. Periodically the number of feeding animals at each station was recorded. In addition we tested for the IFD when we went to the Publix grocery store, observing how customers distribute themselves among moving lines at the cashiers. The results of the experiments were not all the same. At some of the

2 sites the evidence supported the Ideal Free Distribution Theory, whereas at other sites the theory was not supported. INTRODUCTION An organism will behave in a way to maximize its chances of survival. This is evident in the ways organisms choose their habitats and food sources. Models of this behavior predict that individual organisms should distribute themselves among habitats and sources of food in a way that maximizes the energy intake of their foraging efforts. If an area within the habitat provides more food resources at a higher rate than other areas then more organisms should move into that area. The areas within the habitat receiving less food should receive fewer organisms. Over all, the organisms should distribute themselves proportionally to the amount of food. In this model, the Ideal Free Distribution (IFD) model, it is assumed that competing individuals distribute themselves in a way that each individual receives equal amounts of food (Fretwell and Lucas, 197). As an example, if there are eight dogs and two bowls of dog food, bowl A has two pounds of food and bowl B has six pounds of food, the dogs would distribute themselves proportionately, two dogs to Bowl A and six dogs to bowl B. This would insure that no dog would improve its food intake by moving to another bowl and each dog would get the same amount of food. The IFD Theory allows one to make predictions regarding foraging behavior. The IFD Theory incorporates several assumptions. These include the following: 1) that all organisms are free to choose the resource, ) that all the organisms have

3 knowledge of the availability of resources, 3) that organisms are free from competition and ) the resource intake decreases with organism density. The purpose of these experiments is to see how different animals distribute themselves using the IFD theory as a way to examine their behavior. Several experiments were conducted at various sites, including Pinecrest Gardens, Monkey Jungle, and Publix. It was hypothesized that at each site the organisms would demonstrate behavior that would match the Ideal Free Distribution Theory. MATERIALS AND METHODS Pinecrest Gardens We went to Turtle Pond at Pinecrest Gardens, where we organized into four groups about a meter from one another. We randomly distributed cups filled with fish food pellets and one of four spoons (15ml, 5ml,.5ml, and 1.5ml). Then every 5 seconds, for 17 trials, we threw food into Turtle Pond. We waited for 1 seconds after throwing the food and then counted the number of fishes and turtles within a meter of each group. We repeated this for four trials, every day for two days, alternating between two parts of Turtle Pond, South and North, each time switching positions and spoon sizes randomly. The species of turtles were the western painted turtle (Chrysemys picta belli), red eared turtle (Trachemys scripta elegans), and eastern spiny softshells (Apalone s. spinifera). We also saw different species of fishes called koi (Cyprinus carpio), tarpon (Megalops atlanticus), gar (Lepisoteus platyrhincus), and the spotted tilapia (Tilapia mariae).

4 Monkey Jungle We went to the Java macaque compound, which was in Monkey Jungle, where we randomly set up into two different groups. We got two buckets and filled one with 75.5g of grapes and 3.7g of marshmallows and the other twice as much of each food type. Then we placed the food from the bucket onto the ground. Then we waited for 15 seconds and then started counting the number of monkeys that came to feed. After four minutes we changed to 3 second intervals. Then we went to the squirrel monkey compound where we collected a second set of data. Again we randomly set up into two different groups one for the large pile of food which was 15g of grapes and g of marshmallows, one for the small pile which was 75.5g of grapes and 3.7g of marshmallows. We repeated the experiment 3 second intervals throughout. Publix Three team members went into Publix. Two of the members reported when someone would leave a checkout line via cell phone to another team member outside the store. Only one person reported when someone entered the line to the other team member on that phone line. So in total four phones were used. We did not take into account the express line because this would violate the assumption of free distribution of the IFD, because the express limits you to ten items or less, which is not a free choice. RESULTS

5 Pinecrest Gardens As we added fish food more fishes and turtles came to the area, increasing the total of number of animals (Fig 1). The largest number of animals went to the sites with the largest spoon size and the second largest number of animals went to the sites with the second largest spoon size (Fig ). There was very little difference in the number of animals between the two smallest spoon sizes. Based on a chi-square test the pattern did not match the IFD (χ =9.3, 3df, p>.5), because the smallest spoon size (1.5 ml) had a few more animals than the (.5 ml) spoon size. When only the turtles were considered in the analysis, they did follow the IFD (χ =1.39, 3df, p>.1; Fig 3). Most of the turtles went to the largest spoon size rather than the smaller spoon sizes. Ignoring the smallest spoon size, the turtles followed the IFD; the turtles were distributed proportionately among the spoon sizes. The number of turtles with the smallest spoon size was equal to the.5 ml spoon size, so it did not follow the IFD. The fish, when considered alone, did not follow the IFD (Fig ). The larger spoon sizes had more fishes than the smaller spoon sizes, but the 15 ml spoon size and the 5 ml spoon size were nearly equal, just like the.5 ml spoon size and the 1.5 ml spoon size. Monkey Jungle The squirrel monkeys did not show an IFD consistently throughout the experiment (Fig. 5). Over time it seemed that more squirrel monkeys distributed themselves to the larger pile of food. There were intervals when the squirrel monkeys suddenly decreased. This occurred at 5 sec, 135 sec, 5 sec, 85 sec, and at 5 sec.

6 Frequently capuchin monkeys and howler monkeys would appear at the food site and would chase off the squirrel monkeys. The Java macaques also did not show IFD consistently throughout the experiment (Fig. ). IFD seems apparent at 5 sec., 15 sec., and 5sec. The Java macaques chose the smaller piles more often. It was noticed that the dominant Java macaques chased the non-dominant macaques away. In general, most of the squirrel monkeys were at the larger food pile; however they did not meet the IFD criteria in that to 1 proportion was not seen in the distribution (Fig. 7). The Java macaques distributed themselves evenly between both piles. An IFD was not observed for the average number of monkeys (Fig. 7). In both cases the distribution did not differ from IFD (squirrel monkey: χ =.1, 1df, p>.5; java macaques: χ =.89, 1df, p>.5), but that was because there were two few monkeys overall. Publix The majority of the people at Publix went to the larger lines (Fig. 8). IFD was not shown because we expected more customers to have chosen the smallest lines rather than the larger lines. It was noticed that people would often change from line to line. DISCUSSION Pinecrest An IFD was not observed in Turtle Pond because the fishes and the turtles as a group did not distribute themselves proportionately to food input. Over time the amount

7 of fishes and turtles that appeared increased. This might have occurred because the fish and turtles had realized that the food was being distributed in the pond. It was evident that the positions with the larger spoon sizes had more animals than the others. Fish and turtles may not have been able to tell the difference between the.5 ml and the 1.5 ml. It was noticed that, at the 1 second lag time between throwing time and counting time, food in the smaller spoon size positions had already been eaten by the fishes and turtles. This may have influenced the results. The fish did not show an IFD. It was possibly not ideal because the fish might not have been able to differentiate between the spoon sizes. The fishes were probably not free to move during the experiment because there were differences in size between the fishes being counted in the different feeding sites. The koi fish and the tarpon were much larger than the cichlids and may have been able to exclude the smaller ones. This might have biased some of the results in the experiment. The turtle population followed the IFD. It was potentially not ideal because the turtles might not have been able to differentiate between the spoon sizes. However, it was likely a free situation, because the turtles were more or less the same size. Monkey Jungle In general the squirrel monkeys tended to go to the larger pile of food, illustrating the IFD, but it was not exactly as predicted by the IFD. This might have been caused by despotic behavior by larger non-squirrel monkeys species (i.e., capuchins and howlers) chasing the much smaller squirrel monkeys away. Squirrel monkeys would forage in big groups in the absence of dominants.

8 In the Java macaque population the dominant macaques did not allow a free distribution either. These species of monkeys have a social hierarchy in which the dominant males and higher level females exclude lower ranked individuals in feeding (S. Evans, pers. com.). A second factor that might have influenced the results was motivation. Both squirrel monkeys and Java macaques might have been fed before the experiment, which decreased their desire to feed. A final factor that might have influenced the results was a possible incorrect choice of food resources used by the researchers in the experimental design. For instance, it seemed that the monkeys preferred marshmallows over grapes. It is not known by the researchers if the monkeys might have preferred other kinds of food resources than the ones we provided. Publix An IFD was not shown at Publix supermarket. It was not an IFD because most people chose the larger lines instead of the smallest available line. Eight lines were used in the study; express lines were not used because they had a criterion of ten items or less, not allowing for free distribution. One factor that might explain why this did not fit an IFD was because time was not used as a measurement and the length of a line did not indicate time spent in a line. Factors that influenced time were periodic price checks, amount of groceries a person may have, and method of payment. It was also observed that many people noticed that their line was not moving quickly and they decided to change to a line that seemed to be moving faster.

9 In conclusion, animals and humans did not always follow the IFD. As mentioned above, there are many factors that did not allow Ideal and Free Distribution to occur. ACKNOWLEDGEMENTS We say thank you to the Howard Hughes Research Institution and the University of Miami for allowing us this opportunity to learn. We would also like to thank Dr. Sian Evans from Monkey Jungle for taking time out of her schedule to inform and be with us during our visit to Monkey Jungle. Mr. Robinson and Dr. DeAngelis for everything; we wouldn t have been able to do all of this without you both. We thank Christy Wolovich and Dennis Wasko for helping us with the monkeys. Ms. Pearson, thank you for being the best undergraduate facilitator. Thank you to Dr. Krempels for helping us gain a better understanding of science. We would also like to thank our knowledgeable teachers Mr. Negrelli and Mrs. Barreto for assisting us this summer. Lastly, we would like to acknowledge Pinecrest Gardens, Publix, and Monkey Jungle for allowing us to collect data. LITERATURE CITED Fretwell, S.D and Lucas, H.L. Jr. (197). On territorial behavior and other factors influencing habitat distribution in birds. Acta Biotheoretica, 19: 1-3

10 number of animals time (seconds) Figure 1. Total number of animals (fishes and turtles) at different amounts of food at different intervals time number of animals spoon volume (ml) Figure. Total number of animals (fishes and turtles) at different spoon sizes, averaged from 35 seconds on.

11 5 number of turtles spoon volume (ml) Figure 3. Total number of turtles at different spoon sizes averaged from 35seconds on. 7 number of fishes spoon volume (ml) Figure.The average total of fishes at different spoon sizes averaged from 35seconds on.

12 number of squirrel monkeys small pile big pile time ( Seconds) Figure 5. Total number of squirrel monkeys at different amounts of food at different intervals. 8 number of Java macaques big pile small pile time (seconds) Figure. The average total of java macaques at different amounts of food at different intervals.

13 number of monkeys big pile small pile java species squirrel Figure 7. Total number of monkeys in different piles averaged Number of Choices chose smallest Line Choices chose larger Figure 8. Total number of line choices made at Publix. The chose smallest lines means that they chose one of the shortest lines and choosing the larger line meant that they went to the other lines.