Algal blooms can have negative effects on an ecosystem by dominating its phytopl
ID: 3157078 • Letter: A
Question
Algal blooms can have negative effects on an ecosystem by dominating its phytoplankton communities. Gonyostomum semen is a nuisance alga infesting many parts of northern Europe. Could the overall biomass of G. semen be controlled by grazing zooplankton species? A research team examined the relationship between the net growth rate of G. semen and the number of Daphnia magna grazers introduced in test tubes. Net growth rate was computed by comparing the initial and final abundance of G. semen in the experiment, with a negative value indicative of a decrease in abundance. Here are the findings:
Using the above information, software tells us that the least-squares slope is b = 0.5286 with standard error SEb = 0.1059.
(a) What is the t statistic for testing H0: = 0? (Round your answer to two decimal places.)
t =
(b) How many degrees of freedom does t have?
df =
Use this table to approximate the P-value of t against the one-sided alternative Ha: > 0 (as the grazers would be expected to reduce algal growth).
0.001 < P < 0.0025
0.0025 < P < 0.005
0.005 < P < 0.010
0.010 < P < 0.020
0.020 < P < 0.025
What do you conclude? (Use = 0.05.)
-There is strong evidence that the population slope is negative.
-There is not enough evidence to conclude that the population slope is negative.
Number of D. magna grazers 1 2 3 4 5 6 Net growth rate of G. semen 1.9 2.5 2.2 3.9 4.1 4.3Explanation / Answer
a)
t = b / SEb = -0.5286/0.1059 = -4.991501416 [ANSWER]
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b)
As n = 6, then
df = n -2 = 4 [ANSWER]
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c)
Using table, at df = 4, we see that
OPTION B: 0.0025 < P < 0.005 [ANSWER]
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d)
As 0.0025 < P < 0.005, then P < 0.05, so
OPTION A: -There is strong evidence that the population slope is negative. [ANSWER, A]
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