ECOL203/403 Assignment 2 Niche Breadth and Resource Partitioning
Introduction to Niche Breadth and Overlap
Before you begin this exercise (or read any further) you should:
1. Read Chapter 22 of Attiwill and Wilson (2006), â€˜The Nicheâ€™ page 349 â€“ 360.
2. Make sure you have the â€˜Pre-formatted Spreadsheet for Data Analysisâ€™ niche_spreadsheet.xls file from the Assignment 2 folder
3. It is also advisable to read through this exercise completely before starting on the spreadsheet in excel.
Background to the Data
Pademelons of Northeastern New South Wales
There are two pademelon species that inhabit rainforest in Northeastern NSW. The rednecked pademelon (Thylogale thetis) and the red-legged pademelon (T. stigmatica). In this exercise, you are asked to examine the niche breadth of each of these rainforest species, and determine the degree to which each species diet overlaps with the other. You will then present and briefly discuss your results. The data-set is a fictitious one, but is based loosely on what we know of the ecology of these species â€“ so for the purpose of the exercise, assume these data were collected from pademelons inhabiting rainforest at Dorrigo National Park in northeastern New South Wales (see below for more details).
Calculating Niche Breadth and Overlap Download and open the excel spreadsheet exercise called â€˜niche_spreadsheet.xlsâ€™ from the Assignment 2 folder on the unit website. Spend a minute looking around this spreadsheet. You will notice there are
columns for each of our two pademelons species, then a whole lot of blank columns that you need to calculate (p, p2 etc) for each species. First, look at the columns labelled â€˜T. thetisâ€™ and â€˜T. stigmaticaâ€™. These correspond to dietary data gathered from 10 individual pademelons of each species from the rainforest at Dorrigo National Park, in NE NSW. For each individual animal collected, 50 randomly selected plant fragments were taken from the sacciform forestomach (the first part of the stomach), giving a total of 500 fragments (50 fragments x 10 animals) per species (see the tally at the bottom of each column, which equals 500). Next, look at the other columns that follow each species. Unlike Assignment 1, where I walked you through the calculations, this time you are going to write these simple formula from scratch and do the sub-calculations that are needed to work out the breadth and overlap values that appear in the yellow cells below the data rows (but these should calculate automatically as you fill the empty cells above). For each species, the column labelled â€˜pâ€™ is the proportion that each food type contributes to overall diet (for example, there were 78 Trifolium fragments, from a total 500 fragments of all food types, so under pthetis for the food item â€˜Trifoliumâ€™ you would divide 78 by 500 to give a value of 0.156 (or in that cell, you would write the formula â€˜=D2/D$17â€™). The column pthetis2 is simply the proportion squared, and further along (after the calculations for T. stigmatica) you are asked to calculate pthetis* pstigmatica â€“ which is simply one value multiplied by the other. If you do these as excel formulas (i.e. D2/D$17 instead of 78/500), you can easily copy down the cells to give the corresponding value for each food type and pademelon species combination. [HINT: remember that a â€˜$â€™ between the â€˜Dâ€™ and â€˜17â€™ in the example given tells excel to keep the â€˜17â€™ constant for each successive row as you copy the formula down the rowsâ€¦] Once you have completed these calculations, the cells in pale yellow should automatically fill with the results you are looking for. If you have done this correctly, the value for Levin's Measure of Niche Breadth should be 6.280 for T. thetis, and 7.352 for T. stigmatica. Correct? If yes, well done! (in which case, you can assume all your other calculated values are also correct). If no, then re-read the instructions above and recalculate the cells. If you get really stuck, post a message to Moodle, or try to contact me. The next thing you should do is read up on Niche Breadth and Overlap â€“ the extract of the chapter on these calculations by Charles Krebs that appears under the Assignment 2 area will help you to understand what these measures are, and how they were calculated. This is essential reading.
Writing the Assignment Once youâ€™ve calculated the niche breadth and overlap values for your two species of pademelon (and understand what they mean by reading the supplied literature) you are in a position to start writing the assignment. Similar to Assignment 1, this assignment is to be completed via answers to questions, posed below. The difference, however, between this assignment and Assignment 1 is that some of your answers will require you to have researched the ecology of the two species that are the focus of the assignment (and you should cite sources and give references according to the APA style guide in your answers). Answer the following questions: Question 1: What values did you calculate for Levinâ€™s measure of standardized niche breadth for each of the pademelons species? What do these results mean in terms of the diet of the two pademelons species? Do these results fit with what you know of the dietary ecology of these species from the literature? Elaborate with a brief discussion, citing a minimum of two peer-reviewed papers [max. 350 words, not including references] Question 2: What was your calculated value for Percentage overlap between T. thetis and T. stigmatica? Is this considered a large overlap in the context of other studies that you know of where the diet of two mammals has been compared? Discuss, with appropriate citation to at least one peer-reviewed paper. [max. 350 words, not including references]
Uploading of Assignment Upload your completed assignment as a pdf. There is no need to upload your spreadsheet calculations as part of this assignment.