Homework Assignment 2

INSTRUCTIONS:  Data sets for each study are in the accompanying Excel data file (Homework 2 data 2022.xls); one worksheet per data set. You should use R to complete this assignment, include pertinent sections from the computer printouts in your answer, and highlight the relevant values on the printouts.  Show all hand calculations.

• This assignment is due on Thursday, March 31^th.
• Please submit your homework through Canvas.
• Please follow the standard homework answer format (see document on Canvas for details).
• UNLESS THE QUESTION INSTRUCTS OTHERWISE, you must check parametric test assumptions and, if violated, determine the best approach for dealing with those violations.

Question 1:

Animals often possess phenomenal navigational capabilities – even without smartphones! The cues they use to navigate vary, among them are: magnetic fields, sun compasses, celestial maps, sound, and olfactory cues. A researcher was interested in whether fiddler crabs that foraged along the water’s edge at low tide used a sun compass, magnetism, or both to help them relocate their burrows high on the beach. So she conducted an experiment in which she collected 48 crabs at random from an area and randomly assigned 12 crabs to each of four conditions: (a) eye-cups were placed over their eyes so that they were blindfolded to disrupt orientation using the sun, (b) a small magnet was glued to their back to disrupt magnetic navigation, (c) both blindfolded and outfitted with a magnet, and (d) a control where the crabs were handled but no eye-cups or magnets applied to them. Each crab was then released near the water’s edge 10m from their burrow and the time it took each of them to find their burrow (in seconds) was recorded.  Does the navigational capability of crabs differ among the experimental treatments? CHECK ASSUMPTIONS.

Question 2:

The pathogenic fungus Cryphonectria parasitica was introduced into North American forests in the early 1900’s from Asia and over the next few decades killed over 4 billion Chestnut trees (Castanea dentata), dramatically changing the ecology of American forests.

One study investigated whether point mutations in an autoimmune gene within Chestnut trees might influence their susceptibility to infection by the fungus, as compared to a non-mutated gene. To do so, researchers took tissue samples from 40 trees total that varied in 3 point mutations plus non-mutated trees (10 S-type, C-type, 10 E-type, 10 non-mutated control) and measured the number of fugus infected tree cells per mm of tissue sample.  Do any of the gene mutation types (S, C, or E) confer more resistance to the fungus compared to the non-mutant control? CHECK ASSUMPTIONS,

Question 3:

A study was conducted to determine if temperature tolerance in an endangered species of coral varied among individual corals sampled from randomly selected locations on reefs in the Florida Keys. If so, one might suspect that this physiological response varied due to genetic isolation of subpopulations exposed to different natural temperature regimes. Therefore, researchers randomly selected six locations (labeled A – F) along the Florida Keys reef tract from which they collected seven live coral samples per location. The coral samples were brought to a marine laboratory where each coral was subjected to a high seawater temperature (30^oC) and their physiological response (measured as % of maximum photosynthetic output) determined using pulsed amplitude flourometry. Does % photosynthetic efficiency in corals vary more among locations or among individual corals within a location? What percentage of the variation in photosynthetic efficiency is attributable to differences among locations versus individual corals?

Question 4:

An experiment was conducted to determine if the growth of three different species of tree snails common in Florida (manatee treesnail, Drymaeus dormani; West Indian Bulimulus, Bulimulus guadalupensis; lined forest snail, Drymaeus multilineatus) changes when exposed to different concentrations (0 = control and 10, 15, 20, 25, and 30ppm) of an herbicide suspected of being a growth inhibitor. Individuals of each snail species were randomly assigned to aquaria containing natural tree bark  and then each aquarium was randomly assigned a concentration of the herbicide to be sprayed on the tree bark in each aquarium. After 60 days, the mean change in snail growth (expressed as % change) in each aquarium was determined.  Does exposure to any of the concentrations of the herbicide effect the growth of any of the snail species?

Question 5:

It is hypothesized that the length of the tibia (leg bone that affects jumping ability) differs among four species of mice (Florida mouse, cotton mouse, oldfield mouse, eastern harvest mouse) that dwell in Florida, but may also be influenced by their location habitat. So researchers collected 10 mice of each species from each of five different randomly selected locations in Florida. The average length of the tibia of the 10 mice from each location was then calculated yielding a single mean tibia length for each species per location. Does tibia length differ among mice species? Does location influence that result?