These pages were developed and are maintained by Mark Decker.
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The test site
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I am actively involved with developing multimedia content both for use in the courses the General Biology Program teaches as well as materials to complement textbooks. Periodically I will post some of these materials here in order to facilitate feedback from interested parties.
Most of this material will be in either Shockwave or Flash format meaning you will need the appropriate plugin in order to view the material. Both of these plugins are available for free from Macromedia's web site.
If you find any of these materials useful please 1) tell me so! and 2) feel free to use them in the classroom. However, please do not redistribute them in any form.
Finally, please keep in mind that these are materials currently under development and may be only partially effective at what each attempts to accomplish (that's the point of posting them here, right?). I make no guarantees that they will work on your system.
This is a very simple application that allows the user to explore either the exponential population growth model or the logistic population growth model with discrete generations. The latter is interesting in that as "r" (the per capita rate of increase) increases, population growth moves from a stable approach to "K" (carrying capacity), to damped oscillations, to stable oscillations, to chaos.
This little application provides the user the opportunity to examine the effects of three agents of evolution -- natural selection, gene flow, and genetic drift -- on the frequency of an allele at an arbitrary locus. The user can set values that affect the strength of each of these forces to examine how each works independently or how they can interact. Output is the ferquency of the alelle across the number of generations set for each simulation.
"Hungry Little Fish" is meant to accomplish the same general goals as "Tasty Little Ants" -- promoting an understanding of the action of natural selection -- but with no understanding of population genetics required. Here the student is a passive observer of a small (starting out with only four individuals) school of fish that are feeding on small prey items. The fish differ in terms of the shape of their mouthparts and therefore each phenotype can only use only one particular type of prey. The fish feed until half of the prey population is consumed at which time the application determines whether each individual has gathered enough resources to 1) survive or 2) survive and reproduce. The student can change the proportion of the prey base that is each of the four prey types so that (hopefully) they can explore the effects of habitat characteristics on the direction of selection.
This simulation works like "Hungry Little Fish" except the user is the predator feeding on beetles. There are two environments ("tree bark" and "foliage") and the user completes four rounds of predation on one enviroment, the results (allele frequencies per generation) are plotted, and then you move on to the other environment to restart the simualtion.
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"Numerical superiority of asexual reproduction"
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The evolution of sexual reproduction has been a difficult trait for evolutionary biologists primarily because the built-in costs involved with reproducing sexually are very large. This simple simulation is meant to demonstrate the magnitude of these costs by showing that -- all else (especially the survivorship of sexually and asexually produced offspring) an asexually reproducing female should quickly out-reproduce a sexually reproducing female.
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"Selection against altruism: individual-level selection"
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Like the evolution of sexual reproduction (see above), the evolution of altruism has also been a difficult trait for evolutionary biologists to explain. This simulation demonstrates how individual-level selection should quickly eliminate an altruistic phenotype from a population. In the simulaiton, "benefit" and "cost" refer to the benefit to the recipient and the cost to the actor of the altruistic act, respectively, in terms of numbers of offspring. These values can be set only at generation 1 (i.e., after pressing the "Reset" button).
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"Differential reproductive success"
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This simulation demonstrates the simple effect of differential reproduction (natural selection) on relative representation of phenotypes in a population of beetles. When the average number of offspring is equal for the two phenotypes, the composition of the population does not change. However, even a small difference in the average number of offspring produced will lead to the population changing relatively quickly.
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"Reproductive potential of elephants"
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All populations have the innate capacity for tremendous populaiton growth. After reading Malthus, Darwin realized that this created a "strugglefor existence" among individuals of a population and here was a mechanism by which populations could evolve adaptively. To make this point, Darwin discussed the reproductive potential of a population of elephants, using some realistic values for reproductive characteristics (see assumptions on the simulation page). This simulation demonstrates how a startig population of two elephants can within a relatively small number of generations outgrow the Earth itself. (Be patient. Nothing seems to happen at first, but eventually you will see the red dot representing the area covered by the elephant population start to grao quite dramatically.)
This simulation examines the effects on immigration rate of island size and distance of island from a mainland source pool of immigrants. Clicking the "go" button causes red dots representing individuals (or species) to move out randomly from the "mainland." When these indivdiuals/species land on an island they remain there. You can have up to four islands that can differ in terms of size (use radio buttons) and isolation (drag islands into desired position). Add/delete islands through use of the radio buttons for each of the four islands at the bottom of the animation. The numbers of immigrants on each island are provided in the boxes at the bottom.
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