BSCI 106 Fall 2009 Dr. Sara Via Study Questions #2: Competition & Predation 1. How could you show experimentally that intraspecific competition affects survival or reproduction in a real population? Grow populations of different sizes (densities) under controlled conditions.. See if age-specific fecundity [m(x)], and/ or age-specific survival [l(x)] are the same across densities (no competition), or different across densities (intraspecific competition). With competition, fecundity will decline with density and/or mortality will increase. 2. How could you show experimentally that interspecific competition affects survival or reproduction in a real population? Grow and maintain the two species both separately and together. If the number of one or both species is reduced when species are together, this is evidence for interspecific competition. Also, showing that survival, growth or reproduction is decreased by the presence of the other species would work. 3. Now apply what you know. You obtain an internship for the summer in the Biology Department, working with a plant population biologist that studies prairie plants. She is interested in knowing whether a particular species of plant is subject to intraspecific competition. For your summer project, she has asked you to design an experiment to test the hypothesis that intraspecific competition could limit the growth of this prairie grass population. What kind of experiment would you suggest to her? (no need to tell me details like how many observations you will make, just tell me the kinds of treatments [and controls, if necessary] that you will perform. Hint: think about the experiments I described in class) To test for the possibility of intraspecific competition, you need to show that lx(age specific survival) and mx(age specific fecundity, including age at which reproduction begins), survivorship to some date, and/or total number of offspring are altered by density in the direction that will curb population growth. To do this, grow your plant in a set of different densities, from sparse to crowded, and measure lx, mx. survivorship to some key age or total number of offspring. 4. Same as #1, but instead of intraspecific competition, design an experiment to test whether this population is subject to interspecific competition. To test for interspecific competition, you could grow your plant with different densities of another species (like the wheat/Bromus example), or you could grow the two species together and also separately (like the ant/rodent example). A change in the survival or reproduction of your target species in the presence of the other one in the direction that would lower the rate of population growth is evidence for interspecific competition. 5. Why don't predators always drive their prey extinct? Describe the hide-and-seek behavior that can permit predators and prey to coexist in complex environments.
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