Background Information s8

Biology Student Enduring Understanding EQ: Is predation a bad thing? Interactions in nature determine the balance of ecosystems. Broad Brush Knowledge Pop Goes the limiting factors, conservation Concepts Important to Know and Understand Weasel Limited Resources, Interaction Among Organisms Core Objectives 1. Students will use scientific methods and safe lab practices Targeted Skills while conducting field and laboratory investigations. models/diagrams, relationships, making generalizations, analyze, predict, cause & effect, concept mapping 3. Investigate and explain the flow of energy through an ecosystem including food chains, food webs, and trophic levels within food pyramids.

PURPOSE Illustrate a predator-prey relationship and analyze the affect this relationship has on the dynamics of a population.

BACKGROUND INFORMATION A population is all the individuals of the same species within a community. The maximum rate of reproduction of a population is its biotic potential. This is the rate at which a population would produce offspring if every new individual lived and reproduced at maximum capacity. Populations never achieve their biotic potential because the environment can only support a limited number of organisms. The maximum number of individuals of a species that can be supported by the environment is called the carrying capacity. Populations tend to stabilize, or stop growing in size, when the carrying capacity of the environment is reached. The environmental factors that limit the size of populations are called limiting factors. Predators are considered limiting factors because they can limit the size of the prey populations. Conversely, the availability of prey is a limiting factor on the populations of predators.

Populations in nature are often controlled by predation. The regulation of a population by predation takes place within a predator-prey relationship, one of the best-known mechanisms of population control. The relationship between mice and weasels is one example of a predator-prey interaction that affects population growth. In this lab, a new meadow develops in a forest as a result of a fire. Mice migrate into the meadow and begin to reproduce. As the mouse population increases, a weasel is also attracted to the meadow. In the following exercise the meadow (habitat) is represented by a dish, the mouse population (prey) is represented by popcorn kernels, and the weasel population (predator) is represented by a spoon.

MATERIALS (by group) Small plastic bowl (habitat) 100 popcorn kernels (mice/prey) plastic spoon (weasel/predator) calculator

PROCEDURE Rules 1. The surviving mice of a generation always double their numbers. 2. In each generation, at least 10 mice are initially present (by immigration if necessary). 3. The carrying capacity is 100 mice (there cannot be more than 100 mice). 4. In each generation at least one weasel is initially present (by immigration if necessary). 5. In order for a weasel to survive, it must capture at least 5 mice. For each 5 mice that a weasel captures, it will produce one offspring.

Pop Goes the Weasel - Student (Revised June 8, 2004) (printed 4/8/2018) p. 1 Generation 1 : Begin with 10 mice and one weasel (place ten kernels in the dish). Scooping the spoon once through the dish for each weasel simulates the capture of mice. During the first generation, the weasel does not capture any mice and therefore he dies. The 10 surviving mice double their numbers, therefore, the second generation will begin with 20 mice.

Generation 2 : Since there were no surviving predators, we must assume that a weasel immigrated into the meadow. Scoop once through the dish, picking up 4 kernels. This is not enough mice for the predator to live and reproduce. The 16 surviving mice double their numbers, therefore, the third generation will begin with 32 mice.

Generation 3: Again, we must assume that a weasel immigrated in to the meadow. Scoop once through the dish, picking up 7 kernels. This is enough for the weasel to survive and produce one offspring. Double the mouse population; the fourth generation will begin with 50 mice.

Generation 4 : There are two predators to begin generation four. Scoop once through the dish for the first predator (picking up 13 kernels) and once through the dish for the second predator (picking up 7 kernels). The first predator survives and produces two offspring and the second weasel survives and produces one offspring. Double the mouse population; the fifth generation will begin with 60 mice

Completing the Exercise : Continue until you have completed 12 generations. When simulating the capture of mice by the predator, scoop the spoon through the dish and do NOT look at the dish while you are doing this and do NOT try to scoop up all the kernels. Remember that the initial prey must never fall below 10 and the initial predators must never fall below one. Complete the generations in the chart on your student lab sheet.

(Hint: it would be helpful if you placed all the prey captured by each predator in its own pile so that you can easily determine which predator survived and which reproduced.)

DATA TABLE

Generation Number 1 2 3 4 5 6 7 8 9 10 11 12 Initial 10 Prey Total Prey 0 Captured Prey 10 Survivors Initial 1 Predators Surviving 0 Predators Predator 0 Offspring

DATA ANALYSIS Graphing Create a graph of the “Initial Prey” and “Initial Predators” for all 12 generations. Reference the “Making a Graph” skills worksheet to ensure that you follow all graphing guidelines.

Pop Goes the Weasel - Student (Revised June 8, 2004) (printed 4/8/2018) p. 2 Questions 1. What is biotic potential?______2. Does a population ever reach its biotic potential? Why or why not?______3. What is carrying capacity?______4. What are limiting factors? ______5. What limiting factor seems to determine the size of the weasel population in the meadow in any given generation?______6. What limiting factor seems to determine the size of the mouse population in the meadow in any given generation?______7. Predict what would happen to the mice population if the weasel population were to be permanently removed from this meadow as a result of extinction. ______8. Infer how each of these factors in the concept map below increase the death rate in a population.______

Density-dependent factors

Density-independent factors

Population HUMAN COMPETITION Size DISTURBANCES

DROUGHT AND OTHER PREDATION CLIMATE EXTREMES PARASITISM AND DISEASE

Pop Goes the Weasel - Student (Revised June 8, 2004) (printed 4/8/2018) p. 3