Exercise 2: Quantifying Community Similarity When ecologists examine the species
ID: 209871 • Letter: E
Question
Exercise 2: Quantifying Community Similarity When ecologists examine the species living in different communities, they often quantify composition and richness. Although such data tell us about the species living in community, they do not provide a measure of comparison. To address this need, ecologists have everal indices of community similarity that can range from zero to one. A value of zero indicates that two communities have no species in common, whereas a value of one indicates that two nities have an identical composition of species. One of the most common ways to quantify similarity is Jaccard's index of similarity, developed by the Swiss botanist Paul Jaceard in 1901. Jaccard's index is calculated using the following equation: A+B+X Where A represents the number of species present in ONLY community A, B represents the mumber of species found ONL.Y in community B, and X represents the number of species found in BOTH in communities A and B. For example, consider the table below that lists the species of fish found in each of three stream communities that are at different stages of succession. We can use Jaccard's index to calculate the similarity between Community A and Community B. Community C Community A Community B Rainbow trout Brook trout Brown trout Mudminnow Common shiner Creek shiner White sucker Johnny darter Smallmouth bass Mottled sculpin 1+4+3 JAB = 0.37 This value indicates that there is relatively low similarity in the species composition of Communities A and B. YOUR TURN Use Jaccard's index to calculate the similarity between Communities A and C and between Communities B and C. Based on these calculations, which communities are the most similar to each other?Explanation / Answer
JAC,
A (Species only in community A) = 3
C (Species only in community C) = 6
X (Species common in A and C) = 1
JAC= X / A + C + X = 1/ 10 = 0.1
JBC,
B (Species only in community B) = 2
C (Species only in community C) = 2
X (Species common in B and C) = 5
JBC= X / B + C + X = 5 / 9 = 0.556
Q.2. Jaccard's index is maximum for BC hence communities B and C are the most similar one.
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