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Unformatted text preview: LAB #9 Predator-Prey Problems Goal : Investigate the interaction of species via a particular predator-prey problem. Required tools : Matlab routines pplane , dfield and fplot . Discussion You will examine a predator-prey problem that has historical roots as noted in the following excerpt of an article. Predator-Prey Problem: Why the Percentage of Sharks Caught in the Mediterranean Sea Rose Dramatically During World War I In the mid 1920s the Italian biologist Umberto DAncona was studying the pop- ulation variations of various species of fish that interact with each other. During his research he came across some data on percentages-of-total-catch of several species of fish that were brought into different Mediterranean ports in the years that spanned WWI. The data gave the percentage-of-total-catch of selachians (sharks, skates, rays, etc) which are not very desirable as food fish. The data for the port of Fiume, Italy, during 1914-1923 was as follows: 1914 1915 1916 1917 1918 1919 1920 1921 1922 1923 11.9% 21.4% 22.1% 21.2% 36.4% 27.3% 16.0% 15.9% 14.8% 10.7% DAncona was puzzled by the very large increase in the percentage of selachians during the period of the war. Obviously, he reasoned, the increase in the percentage of selachians was due to the greatly reduced level of fishing during this period. But how does the intensity of fishing affect the fish population ? The answer to this question was of great concern to DAncona in his research on the struggle for existence between competing species. It was also of concern to the fishing industry, since it would have obvious implications for the way fishing should be done. What distinguishes the selachians from the food fish is that the selachians are preda- tors , while the food fish are their prey ; the selachians depend on the food fish for their survival. At first, DAncona thought that this accounted for the large increase of selachi- ans during the war. Since the level of fishing was greatly reduced during this period, there were more prey available to the selachians, who therefore thrived and multiplied rapidly. However, this explanation does not hold any water since there were also more food fish during this period. DAnconas theory only shows that there are more selachi- ans when the level of fishing is reduced; it does not explain why a reduced level of fishing is more...
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- Spring '08