ANSC 455: Animal Behavior
Laboratory Exercise 6
"Birds of a feather"



Many animals, particularly herbivores, spend a large portion of their day searching for food. These animals must balance their need for nutrients with their avoidance of predators. In order to maximize both of these aspects of survival, many animals congregate together in herds, flocks, or schools. The principle behind this phenomena is called optimum foraging theory.

This theory assumes that animals will try to optimally search for food. That is, they will find the best balance between energy expenditure to find food and other energy costs. One cost is predator defense, that is the amount of energy an animal uses to look out for predators. By grouping in herds (flocks/schools), animals can reduce this cost by sharing the "duty" with other animals.

Within a group of animals, there are behaviors observed that are not seen in individual animals. It is believed by some researchers that groups of animals display a collective behavior. That is to say, that a herd of animals often behaves as if it were a single animals. This is only one of the several emergent behaviors found in groups of animals.

A few of the other behaviors that emerge from a group of animals are a dilution effect, a confusion effect, an odd prey effect and a selfish herd effect. The dilution effect is the idea that the chance of an individual being captured by a predator decreases as group size increases. This is because the predator only takes a single or a limited amount of prey in each attack.

The confusion effect is based on the fact that it is difficult to focus on multiple stimuli at the same time. Predators have a hard time focusing on a specific individual, when many other animals are escaping from them at the same time. This effect can be attributed to the fact that students have a difficult time of retaining what they study when there is a television on.

The third type of effect that emerges from animals in a group is the odd prey effect. The idea behind this effect is that if an individual differs from the rest of the group, it is more likely to be attacked and captured by the predator. The odd prey effect may negate the confusion effect. This is where the adage, "Birds of a feather flock together" may have come from.

Another type of effect that often emerges from animals in a group is the selfish herd effect. The selfish herd principle was conceived by Hamilton (1971) and is based on the idea that each individual in the herd will try to be at the group center to avoid predation. Hamilton conceptualized this principle with frogs attempting to avoid being on the perimeter (See figure 1).

Figure 1. Hamilton's Jumping Frogs.

In today's lab we will explore the phenomena of herding (flocking/schooling) behavior during foraging, as well as the dilution and confusion effects through several simulations.
Feeding Facilitation Simulation
Part 1

Each person will be given a small plastic bag. During the allotted amount of time, each individual will be allowed to pick up as many toothpicks as he/she can. Multiple toothpicks may be picked up at one time. There is no talking allowed during this activity.
Part 2

Each person will be given a small container with a small hole in the top. During the allotted amount of time, each individual is allowed to pick up as many toothpicks as he/she can. Only one toothpick at a time may be picked up. Any individual caught picking up more than one toothpick at a time will be declared dead and removed from the population. Again there is no talking allowed during this activity.
Part 3

Same as part 2, but in addition there will be a predator walking around. Any individual touched by the predator is considered dead and removed from the population. At the end of the third part record the number of toothpicks collected for each part of this simulation on your data sheet.
Dilution and Confusion Effects Simulation Procedure

The class will be divided into three groups. Working in pairs within those groups, students will toss golf balls to their partners in a manner that is not impossible to follow, but requires concentration to catch. The golf balls must be caught in the hands only to count as a captured prey. The catcher and the tosser should stand approximately eight (8) feet apart. Each student will get the chance to act as tosser and catcher for a total of 12 balls for group sizes 1, 2, 3, 4, and 6 (i.e., toss 12 single balls, 6 pairs, 4 trios, 3 sets of four, and 2 sets of six). Record the amount of catches made for each group size for each individual in the class on your data sheet.

Bibliography

Bejda, Vickie. 1995. Feeding facilitation: A lesson in evolution and sociobiology. Online URL: http://www.gene.com/ae/AE/AEC/AEF/1995/bejda.html

Burk, Theodore. Simulation the dilution, confusion, and odd prey effects. An Animal Behavior Exercise from the Nebraska Behavioral Biology Group and Biology Department, Creighton University, Omaha, Nebraska

Hamilton, W. D. 1971. Geometry for the selfish herd. Journal of Theoretical Biology, 31, 295-311.

Assignment
Hand in your data sheet along with the answers to the following questions.
 

1) After watching the video tape of the Feeding Facilitation Simulation, which part of the simulation do you think showed the most herding (flocking/schooling) behavior? What selection pressures do think caused this behavior to emerge in this part of the simulation?

2) From the Dilution and Confusion Effects Simulation, calculate the percent of prey captured for each group size. Based on the class data, do you think a dilution effect was seen in our population? Why or why not? (Hint: If the percentage of prey captured decreases as group size increase, a dilution effect was in operation.)

3) From the Dilution and Confusion Effects Simulation, calculate the percent of successful hunts (any time at least one ball was caught) for each group size. Based on the class data, do you think a confusion effect was seen in our population? Why or why not? (Hint: If the percentage decreases as group size increases, a confusion effect was in operation.)
Name_____________________

Data Sheet
Feeding Facilitation Simulation
Number of toothpicks collected part 1 Number of toothpicks collected part 2 Number of toothpicks collected part 3
__________ __________ __________

Dilution and Confusion Effects Simulation
Predator N Prey Caught With Group Size N Successful Hunts With Group Size*
 
1 2 3 4 6 1 2 3 4 6
_______________ _____ _____ _____ _____ _____ _____ _____ _____ _____ _____
_______________ _____ _____ _____ _____ _____ _____ _____ _____ _____ _____
_______________ _____ _____ _____ _____ _____ _____ _____ _____ _____ _____
_______________ _____ _____ _____ _____ _____ _____ _____ _____ _____ _____
_______________ _____ _____ _____ _____ _____ _____ _____ _____ _____ _____
_______________ _____ _____ _____ _____ _____ _____ _____ _____ _____ _____
_______________ _____ _____ _____ _____ _____ _____ _____ _____ _____ _____
_______________ _____ _____ _____ _____ _____ _____ _____ _____ _____ _____
Total _____ _____ _____ _____ _____ _____ _____ _____ _____ _____
% _____ _____ _____ _____ _____ _____ _____ _____ _____ _____

 

Sample data set for dilution and confusion effects simulation


Predator N Prey Caught With Group Size N Successful Hunts With Group Size*
 
1 2 3 4 6 1 2 3 4 6
Jamie 11 11 9 4 2 11 6 4 2 2
Tobin 12 10 7 6 1 12 5 4 3 1
Mark B. 12 12 10 9 3 12 6 4 3 2
Max 11 8 8 5 1 11 4 4 3 1
Kate 12 10 8 6 0 12 5 4 3 0
Mark V. 12 11 6 7 1 12 6 3 3 1
Christine 10 12 9 3 0 10 6 4 2 0
Phillip 12 9 7 7 0 12 5 4 3 0
Total 90/96 91/96 64/96 47/96 8/96 90/96 43/48 31/32 22/24 7/16
% 94% 84% 67% 50% 8% 94% 90% 97% 92% 44%

 

* A successful hunt is any time at least one golf ball is caught. To calculate the number of potential successful hunts for each group size, multiply the numbers of tosses for the group size by the number in the population. (The number of potential successful hunts for our class at group size six would be 2 [number of tosses for this group size] x 14 [number of people in the population]=28.)


This handout is copyright 1996 by Marina Haynes and Cassandra Moore-Crawford
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