Researchers studying the number of electric fish species living in various parts of the Amazon basin were interested in whether the presence of tributaries affected the local number of electric fish species in the main rivers. They counted the number of electric fish species above and below the entrance point of a major tributary at 12 different river locations. Here's what they found: Tributary Upstream number of species Downstream number of species
Ica 14 19
Jutai 11 18
Japura 8 8
Coari 5 7
Purus 10 16
Manacapuru 5 6
Negro 23 24
Madeira 29 30
Trombetas 19 16
Tapajos 16 20
Xingu 25 21
Tocantins 10 12
A) What is the mean difference in the number of species between areas upstream and downstream of the tributary? What is the 95% confidence interval of this mean difference?
B) Test the hypothesis that the tributaries have no effect on the number of species of electric fish.
C) State the assumptions that you had to make to complete parts (a) and (b).