Many people are probably familiar with the idea of foraging. Whether you see a squirrel rummaging around a park or a hungry college student scanning the local dining hall for something edible, most of us have witnessed it. An optimal forager is defined as an animal that maximizes its net energy gain while foraging. In the wild it is important than animals maximize their net energy gain because it is hypothesized that natural selection acts on animals based on how they maximize it. It is up to each individual forager as to how they forage. The forager could leave the patch when there are no more resources left, or they could stay for a short while and then move on to the next patch. In this week’s lab that’s exactly what we did- maximized our net energy gain while “foraging” on Chamberlain Field on campus. To forage on our college campus we had buckets filled with dried rice and beans. The rice represented patches where we would find prey and the beans represented the prey we were looking for. Each bucket had a different prey density (amount of beans per bucket).
In our lab we split into groups of three. Within each group we rotated three positions: forager, timer, and recorder . The forager was given a styrofoam cup and went to three random “patches” (aka buckets of rice and beans). Each patch was the same distance away from each other. At each patch the forager had a set of rules to follow: you could only use one hand to forage, do not run to the beans, when you are done at each patch mix the beans back into the rice for the next forager. When the forager found a bean, they put it into their styrofoam cup and swirled it around three times. While the forager was looking for the beans, the timer was keeping track of the time the forager arrived at the patch, at what time they found each bean, and when they left the patch. The timer didn’t stop until all three patches had been visited. The recorder wrote down the times that the timer called out when the forager arrived, left, and found beans. Each member of the group took turns being the forager, recorder, and timer.
After every member of the group had a turn, we headed back inside to work on graphing the data we collected. The first graph shown below:
shows the amount of beans found in relation to patch density. Two of the patches I visited when I was the forager had a patch density of forty beans in the patch, the third patch had a density of eighty beans. At the first patch I found a total of 14 beans out of 40. The second patch I found 25 out of 40. The last patch I found 50 out of 80.
The next graph depicts time spent in each patch.
Again, two of my three patches had the same density which is why there are two dots over the same space on the x-axis. At the first patch I spent 39 seconds, the second patch 63 seconds, and at the last patch I spent 103 seconds.
In the next graph, it shows the capture rate.
This show the percent of prey captured in relation to prey density. At the first patch I had a 35% capture rate. At the second patch I had a 38% capture rate. In the last patch I had a 49% capture rate.
In the next graph it shows the Giving Up Time (GUT) or the time in which it took me to leave each patch.
In the patches with a density fo 40, my GUT was the same. To maximize energy gain each forager is supposed to leave the patch when you’ve reached the same optimal energy intake as the other patches. In the first two patches the GUT matched the Marginal Value Theorem, which is the model associated with GUT analysis.
The final graph depicts the Cumulative Gain Curve for all three patches.
The Cumulative Gain Curve is used to show the rate of energy gain between all the patches visited. Patch 1 had a density of 40 and a capture rate of 35%, Patch 2 had a density of 40 and a capture rate of 38%, and Patch 3 had a density of 40 and a capture rate of 49%.
Animals may behave in a similar fashion to the humans in this foraging experiment when there is a lot of competition in the area. In our lab, we were timing ourselves but we had to share patches with other groups so there was a pressure to not take too long per patch. If there is a case of high competition, animals may not have as many resources available or adequate time to forager, so you may see similar data in that situation.
Optimal foraging strategies are important because they help ecologists understand how organisms are selected against with natural selection. An example- besides college students in the dining hall- for how humans exhibit optimal foraging strategies would be in memories. According to Thomas Hills, “We found evidence for local structure (i.e., patches) in memory search and patch depletion preceding dynamic local-to-global transitions between patches”. Hills research shows that humans “forage” for memories with optimal memory recovery in a similar fashion that animals forage for food.
Fast food is becoming a problem for the weight of adults and children in the United States. According to Henry Fountain, it is now a problem for black bears as well. The bears that live near urban and residential areas are less active than bears in the wild. Instead of foraging for more natural food sources, they often forage through garbage. The lack of activity and their diet makes them heavier than bears in a more natural setting. I believe the bears have changed their foraging habits because it requires less energy for them to dig through nearby garbages than to venture out farther away from towns and cities to forage there. Some solutions to encourage bears to stop foraging through garbage and go back to a better, more natural diet, would be to make it harder for them to get into garbage cans and dumpsters and for land developers to work harder to make more green spaces and leave more land untouched so that animals can live in their natural habitat.
References:
Fountain, Henry. “Fast-Food Nation Is Taking Its Toll on Black Bears, Too.” The New York Times, The New York Times, 25 Nov. 2003, http://www.nytimes.com/2003/11/25/science/fast-food-nation-is-taking-its-toll-on-black-bears-too.html.
Hills, Thomas T., et al. “Optimal Foraging in Semantic Memory.” Psychological Review, vol. 119, no. 2, American Psychological Association. Journals Department, 750 First Street NE, Washington, DC 20002-4242. Tel: 800-374-2721; Tel: 202-336-5510; Fax: 202-336-5502; e-mail: order@apa.org; Web site: http://www.apa.org/publications, pp. 431–40, doi:10.1037/a0027373.
Aurora Ecology 