Questions 1. Describe the response variable that was measured in each of the gra
ID: 68030 • Letter: Q
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Questions
1. Describe the response variable that was measured in each of the graphs of stickleback data. Why do you think these variables were chosen, as opposed to something else (i.e. what do these measurements tell you?)?
2a. what differences in resource use (here, what they eat) and in trophic morphology (traits related to feeding) do you notice among the solitary population (Cranby Lake) and the lake with two species present (Paxton Lake)?
b. Why do you think those differences are present? Explain the how natural selection could have caused these differences.
3. What mode of natural selection is operating in each graph (directional, disruptive, or stabilizing)? Do benthic and limnetic sticklebacks occupy different niches?
4. Use the last graph (Fig. 1 on page 4) to answer the following questions:
a. Why do you think the researcher wanted to start with fish with a range of phenotypes from the solitary population in Cranby Lake?
b. Why did the researcher have a treatment where some ponds only contained the fish from the solitary population in Cranby Lake?
c. Why did the researcher have a treatment where fish from the solitary population in Cranby Lake were placed in a pond with limnetic fish from Paxton Lake?
d. Which fish (benthic or limnetic body types) from the solitary population in Cranby Lake grew the fastest in the presence of the Paxton Lake limnetics? Why?
e. Which fish (benthic or limnetic body types) from the solitary population in Cranby Lake grew the slowest in the presence of the Paxton Lake limnetics? Why?
f. Do your answers (to d. and e.) tell you anything about why benthic and limnetic sticklebacks in Paxton Lake might be as different as they are in the first graph, which shows gill raker length in Paxton Lake fish? Explain your answer.
5. a. Fill out the table below for each of the three types of natural selection. The figure on the first page of this activity should help with this question. In each cell of this table, answer the following:
Does the variable (frequencies) or statistic (mean, SD) change? (yes/no)
If the variable or statistic changes, explain how it changes (e.g. increase (+), decrease (-), no change (0)). A description may be necessary for some of these.
Variable or statistic
Type of natural selection
Directional
Disruptive
Stabilizing
Allele frequencies
Genotype frequencies
Phenotype frequencies
Mean phenotype
Variability in phenotype (e.g. SD)
b. Turn what you put into the “Mean” and “Variability in phenotype” cells above into a graph. Use the initial population as the starting point for a mean and standard deviation (SD), and add a bar with an error bar for each of the three types of natural selection. If, for example, you said the mean would increase and the SD would stay the same under a particular type of natural selection, you’d draw a bar that was higher than the initial population mean, with an error bar that’s the same size as the one on the initial population.
Variable or statistic
Type of natural selection
Directional
Disruptive
Stabilizing
Allele frequencies
Genotype frequencies
Phenotype frequencies
Mean phenotype
Variability in phenotype (e.g. SD)
Explanation / Answer
1. Response variables are also known as dependent variables. These are variables of interest, which tell us that the task has been accomplished in positive or negative direction.
Here the response variables are body size. It has been taken because the researcher wants to check whether the size of sticklebacks is being affected by adding limnetics in the pond or not adding any species or not.
In the second graph, response variable is morphological index. It will indicate the growth rate in presence and absence of limnetic species. In presence of limnetic species growth rate decreases with increase in morphological index and vice -versa.
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