Given that resources are not infinite within any ecosystem, a fundamental question in ecology is, “How many species can occur together within a given community?”
You will need to follow the instructions of the excel, fill out the table in word, create the bar graph, and fill out the excel file. READ ALL DOCUMENTS BEFORE TO UNDERSTAND IT CAREFULLY. DO NOT BID IF YOU CANT COMPLETE IT. Should not be too challenging.
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Niche Overlap and Resource Partitioning
Given that resources are not infinite within any ecosystem, a fundamental question in ecology is, “How many species can occur together within a given community?” The Competitive Exclusion Principle states that if two species compete for critical resources in an environment, one of two outcomes results. Either both species coexist, or one species outcompetes the other and drives the other species to extinction (within the community). Coexistence can occur only if the species niches are different enough to limit competition between them. Thus, we often ask, “How do the different species partition the resources in this community?” To answer this question, we need to know how organisms use their environment. One way to do this is to measure niche parameters for one species and then compare it to the niche parameters of another.
One of the niche parameters is niche breadth. This attempts to measure how specialized or generalized a species is within a given environment. A specialist that feeds on only one or two food sources will have a much smaller niche breadth than a generalist that feeds on many kinds of food items. One way of estimating niche breadth is using Levins measure (B) (1968):
Where B is Levins measure of niche breadth, pi is the proportion of individuals found using resource i.
Levins measure of niche breadth is often standardized so that it ranges between 0 and 1. 0 indicates a very narrow niche (specialist) while 1 indicates a wide niche (generalist).
BA is the standardized niche breadth, n is the total number of food items for the species of interest.
A second niche parameter is niche overlap. This measures the degree to which two different species overlap in their use of a particular resource. Estimating niche overlap allows us to determine how different species partition a resource. One approach to measuring niche overlap is MacArthur and Levins (1967) equation:
Where Mjk is the niche overlap of species k on species j.
pij is the proportion of resources i is of the total resources that species j uses.
pik is the proportion that resource i is of the total resources that species k uses.
A second measure of niche overlap is Pianka (1986):
Where Ojk is Pianka’s measure of overlap between species j and species k.
pij is the proportion that resource i is of the total resources used by species j
pik is the proportion that resource i is of the total resources used by species k.
This measure ranges from 0 (no resources used in common) to 1 (complete overlap).
In the following exercise we are going to examine niche breadth and niche overlap between two species that are using the same resources.
Procedures:
To start, let’s look at the what data is initially telling us in the Excel spreadsheet. “Resources” is the range of resource size (think sizes of seeds, 1 is smallest, 10 is biggest). “# users” is telling us the number of organisms in each species that used the resource size.
A. In cell B16 enter =SUM(B6:B15) (you can also use AutoSum tool
B. In cell F16 enter =SUM(F6:F15)
C. In cell C6 enter =B6^2 to square the observed # users. (or = B6*B6)
D. Copy the formula in C6 into C7 through C15.
E. In cell D6 enter = B6/$B$16. Copy this formula into cells D7 through D15. In column D we are calculating the proportion of the total number of resource uses by species 1. (remember $ locks the cell location so when you copy it doesn’t change)
F. In cell E6 enter =D6^2. Copy this formula into cells E7 through E15.
Return to the equations in the introduction. Note that we have calculated some of the values that are part of the equations. We now have to sum the columns.
G. Enter the following:
Cell C16, enter =SUM(C6:C15)
Cell D16, enter =SUM(D6:D15). This should equal 1.
Cell E16, enter =SUM(E6:E15).
Now using the same steps, fill in the calculations in columns G, H, and I for species 2. Remember in column H to change $B$16 to $F$16.
Let’s now calculate the interaction between species 1 and species 2.
H. In Cell J6, enter =D6*H6. Copy the formula in J6 and paste it into cells J7 through J15.
I. In Cell J16, enter =SUM(J6:J15).
Calculating Niche Statistics
With the basic calculations in place, we are now ready to calculate n, B, BA, M12, M21, and O.
A. In cell B18 enter the formula =COUNTIF(B6:B15,”>0″)
B. In cell G18 enter the formula =COUNTIF(F6:F15,”>0″)
Note that this counts the number of cells that contain a value >0.
C. In cell B19, enter =1/E16
D. In cell G19, enter =1/I16
Now let’s standardize B so it measures 0 to 1.
E. In cell B20, enter =(B19-1)/(B18-1)
F. In cell G20, enter =(G19-1)/(G18-1)
To calculate M for species 1 and 2, enter the following:
G. In cell B21, enter =J16/E16
H. In cell G21, enter =J16/I16
To calculate O for species 1 and 2, enter the following:
I. In cells B22 and G22, enter the formula =J16/SQRT(E16*I16)
J. Create a bar graph that shows the M values and O values for species 1 and 2.
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Niche Overlap and Resource Partitioning Answers
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