"Running Head: SAMPLE FINAL LAB REPORT1Sample Lab Report (The Optimal Foraging Theory)NameSCI 207 Dependence of Man on the EnvironmentInstructor Date SAMPLE FINAL LAB REPORT2Sample Lab ReportAbstractThe theory of optimal foraging and its relation to central foraging was examined by usingthe beaver as a model. Beaver food choice was examined by noting the species of woodyvegetation, status (chewed vs. not-chewed), distance from the water, and circumference of treesnear a beaver pond in North Carolina. Beavers avoided certain species of trees and preferredtrees that were close to the water. No preference for tree circumference was noted. These datasuggest that beaver food choice concurs with the optimal foraging theory. Introduction In this lab, we explore the theory of optimal foraging and the theory of central placeforaging using beavers as the model animal. Foraging refers to the mammalian behaviorassociated with searching for food. The optimal foraging theory assumes that animals feed in away that maximizes their net rate of energy intake per unit time (Pyke et al., 1977). An animalmay either maximize its daily energy intake (energy maximizer) or minimize the time spentfeeding (time minimizer) in order to meet minimum requirements. Herbivores commonly behaveas energy maximizers (Belovsky, 1986) and accomplish this maximizing behavior by choosingfood that is of high quality and has low-search and low-handling time (Pyke et al., 1977). The central place theory is used to describe animals that collect food and store it in afixed location in their home range, the central place (Jenkins, 1980). The factors associated withthe optimal foraging theory also apply to the central place theory. The central place theorypredicts that retrieval costs increase linearly with distance of the resource from the central place SAMPLE FINAL LAB REPORT3(Rockwood and Hubbell, 1987). Central place feeders are very selective when choosing foodthat is far from the central place since they have to spend time and energy hauling it back to thestorage site (Schoener, 1979). The main objective of this lab was to determine beaver (Castor canadensis) food selectionbased on tree species, size, and distance. Since beavers are energy maximizers (Jenkins, 1980;Belovsky, 1984) and central place feeders (McGinley & Whitam, 1985), they make an excellenttest animal for the optimal foraging theory. Beavers eat several kinds of herbaceous plants aswell as the leaves, twigs, and bark of most species of woody plants that grow near water (Jenkins& Busher, 1979). By examining the trees that are chewed or not-chewed in the beavers' homerange, an accurate assessment of food preferences among tree species may be gained (Jenkins,1975). The purpose of this lab was to learn about the optimal foraging theory. We wanted toknow if beavers put the optimal foraging theory into action when selecting food. We hypothesized that the beavers in this study will choose trees that are small incircumference and closest to the water. Since the energy yield of tree species may varysignificantly, we also hypothesized that beavers will show a preference for some species of treesover others regardless of circumference size or distance from the central area. The optimalforaging theory and central place theory lead us to predict that beavers, like most herbivores,will maximize their net rate of energy intake per unit time. In order to maximize energy, beaverswill choose trees that are closest to their central place (the water) and require the least retrievalcost. Since beavers are trying to maximize energy, we hypothesized that they will tend to selectsome species of trees over others on the basis of nutritional value.Methods This study was conducted at Yates Mill Pond, a research area owned by the North SAMPLE FINAL LAB REPORT4th Carolina State University, on October 25 , 1996. Our research area was located along the edgeof the pond and was approximately 100 m in length and 28 m in width. There was no beaveractivity observed beyond this width. The circumference, the species, status (chewed or not-chewed), and distance from the water were recorded for each tree in the study area. Due to thelarge number of trees sampled, the work was evenly divided among four groups of studentsworking in quadrants. Each group contributed to the overall data collected. We conducted a chi-squared test to analyze the data with respect to beaver selection ofcertain tree species. We conducted t-tests to determine (1) if avoided trees were significantlyfarther from the water than selected trees, and (2) if chewed trees were significantly larger orsmaller than not chewed trees. Mean tree distance from the water and mean tree circumferencewere also recorded.ResultsSAMPLE FINAL LAB REPORT5Overall, beavers showed a preference for certain species of trees, and their preferencewas based on distance from the central place. Measurements taken at the study site show that SAMPLE FINAL LAB REPORT6beavers avoided oaks and musclewood (Fig. 1) and show a significant food preference.Noavoidance or particular preference was observed for the other tree species. The mean distance of8.42 m away from the water for not-chewed trees was significantly greater than the meandistance of 6.13 m for chewed trees (Fig. 2). The tree species that were avoided were notsignificantly farther from the water than selected trees. For the selected tree species, nosignificant difference in circumference was found between trees that were not chewed(mean=16.03 cm) and chewed (mean=12.80 cm) (Fig. 3).Discussion Although beavers are described as generalized herbivores, the finding in this studyrelated to species selection suggests that beavers are selective in their food choice. This findingagrees with our hypothesis that beavers are likely to show a preference for certain tree species.Although beaver selection of certain species of trees may be related to the nutritional value,additional information is needed to determine why beavers select some tree species over others.Other studies suggested that beavers avoid trees that have chemical defenses that make the treeunpalatable to beavers (Muller-Schawarze et al., 1994). These studies also suggested thatbeavers prefer trees with soft wood, which could possibly explain the observed avoidance ofmusclewood and oak in our study. The result that chewed trees were closer to the water accounts for the time and energyspent gathering and hauling. This is in accordance with the optimal foraging theory and agreeswith our hypothesis that beavers will choose trees that are close to the water. As distance fromthe water increases, a tree's net energy yield decreases because food that is farther away is morelikely to increase search and retrieval time. This finding is similar to Belovskyís finding of an SAMPLE FINAL LAB REPORT7inverse relationship between distance from the water and percentage of plants cut. The lack of any observed difference in mean circumference between chewed and notchewed trees does not agree with our hypothesis that beavers will prefer smaller trees to largerones. Our hypothesis was based on the idea that branches from smaller trees will require lessenergy to cut and haul than those from larger trees. Our finding is in accordance with otherstudies (Schoener, 1979), which have suggested that the value of all trees should decrease withdistance from the water but that beavers would benefit from choosing large branches from largetrees at all distances. This would explain why there was no significant difference incircumference between chewed and not-chewed trees. This lab gave us the opportunity to observe how a specific mammal selects foods thatmaximize energy gains in accordance with the optimal foraging theory. Although beavers adhereto the optimal foraging theory, without additional information on relative nutritional value oftree species and the time and energy costs of cutting certain tree species, no optimal dietpredictions may be made. Other information is also needed about predatory risk and its role infood selection. Also, due to the large number of students taking samples in the field, there mayhave been errors which may have affected the accuracy and precision of our measurements. Inorder to corroborate our findings, we suggest that this study be repeated by others. Conclusion The purpose of this lab was to learn about the optimal foraging theory by measuring treeselection in beavers. We now know that the optimal foraging theory allows us to predict food- seeking behavior in beavers with respect to distance from their central place and, to a certainextent, to variations in tree species. We also learned that foraging behaviors and food selection is SAMPLE FINAL LAB REPORT8not always straightforward. For instance, beavers selected large branches at any distance fromthe water even though cutting large branches may increase energy requirements. There seems tobe a fine line between energy intake and energy expenditure in beavers that is not so easilypredicted by any given theory."