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Predator-Prey Interactions Predation is a density-dependent limiting factor; it is affected by the number of individuals in a given area. For example, the population of a predator can be limited by the amount of prey available. The opposite is true as well. The population of a prey species can be affected by changes in its predator population. If the predator population declines, the population of the prey may increase as a result of less pressure from predators. Scientists have been studying predator-prey interactions for many years, collecting data about both the predator and prey populations over time. In some cases, a cyclical pattern of rising and falling population numbers emerges between a predator and its prey. Scientists have found that this pattern exists in as many as 30 percent of predator-prey populations studied. In some cases, the cycle may occur over a long period, such as ten years. In other cases, one cycle of both populations rising and falling may take only months. In this lab, you will graph and analyze population data for a predator and its prey that was collected previously under laboratory conditions. You will also graph and analyze data collected for a prey population in which the predator was removed. Problem How do predator-prey interactions affect population numbers of both the predator and the prey? Scenario Two species of mites, one which preys on the other, were housed together in a laboratory experiment, along with a realistic amount of food for the prey. The numbers of both populations were monitored. Table 1 contains population data for both Eotertranychus sexmaculatus (prey) and Typhlodromus occidentalis (predator). Procedure 1. Use the data in Table 1 to construct a line graph with two y-axes that shows the changes in the Eotertranychus and Typhlodromus populations. Be sure to correctly label both the x-axis and each y axis. Label x-axis as “Days” and the left y-axis as “Prey”; the right y-axis as “Predator”. Use the following intervals to set up your graph. “Prey” y-axis = 100 mites “Predator” y-axis = 2 mites “Days” x-axis = 5 days 2. Use a BLUE color pencil to draw a line on the graph representing the Eotertranychus population. 3. Use a GREEN color pencil to draw a line on the graph representing the Typhlodromus population. 4. Table 2 contains data about a population of Kaibab mule deer in Arizona in which all predators were removed. Use the data in Table 2 to construct a new graph that shows the changes in the population. Label the x-axis “Year” and the y-axis “# of mule deer (thousands)”. Use the following intervals to set up your graph. x-axis = 2.5 years y-axis = 5,000 mule deer Table 1. MITE POPULATIONS Table 2. KAIBAB MULE DEER Day Eotertranychus (prey) Typhlodromus (predator) 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 105 110 115 120 125 130 135 140 145 150 155 160 165 170 175 180 185 190 195 200 205 210 100 200 600 1100 1400 800 600 280 200 200 220 225 250 300 410 500 875 1590 1800 1900 2100 1750 1350 850 500 500 600 750 700 800 1200 1800 1900 1770 1700 1800 1675 1320 610 200 50 0 0 2 4 12 28 38 29 18 15 9 8 7 3 2 2 4 6 6 17 19 21 29 25 36 22 6 5 12 5 1 1 1 1 2 3 8 19 30 47 31 9 0 Year # of mule deer 1900 1905 1910 1915 1920 1923 1930 1935 1940 2,900 8,000 20,000 42,500 79,000 100,000 10,000 6,200 5,000 Name: __________________________________________________________ Date: ____________________________ Period: _______ Predator-Prey Interactions 1. Mites Graph 2. Kaibab Deer Graph 3. How did the population of Typhlodromus change in relation to the population of Eotertranychus? Approximately how long is one cycle of rising, failing, and rising again (a) in population number and (b) in this predator-prey interaction? ______________________________________________________________________________________________________________________ ______________________________________________________________________________________________________________________ ______________________________________________________________________________________________________________________ 4. How would the following changes affect the population numbers in the TyphlodromusEotertranychus system: (a) the addition of another predator species that also preys on Eotertranychus (b) the addition of another species that Typhlodromus will also eat (c) cutting the Eotertranychus food source in half ______________________________________________________________________________________________________________________ ______________________________________________________________________________________________________________________ ______________________________________________________________________________________________________________________ ______________________________________________________________________________________________________________________ ______________________________________________________________________________________________________________________ 5. What type of graph does the graph for Kaibab deer show? Why did the population crash? ______________________________________________________________________________________________________________________ ______________________________________________________________________________________________________________________ ______________________________________________________________________________________________________________________