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ya�A��%�06>�����Z�5�4:4PU�����!>骳5�wR��GDl In this example, the first sample would be considered more diverse.
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We also acknowledge previous National Science Foundation support under grant numbers 1246120, 1525057, and 1413739. &k�6u�d�[� Evenness is a measure of the relative abundance of the different species making up the richness of an area.
Diversity is variety and at its simplest level it involves counting or listing species. When all species in the data set are equally common, all pi values = 1/R and the Shannon-Weiner index equals ln(R). h�bbd``b`�$�C�`a@��H�� ���0 ��ҡ $���y��%&F�3 %����0 �"
Let’s compute the Shannon-Weiner diversity index for the same hypothetical community in the previous example.
If abundance is primarily concentrated into one species, the index will be close to zero. Creating prescriptions that combine timber and wildlife management objectives are crucial for sustainable, long-term balance in the system. endstream
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We know that N = 65. We are going to examine several common measures of species diversity. %%EOF
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Consider the following example. Simpson’s index is a weighted arithmetic mean of proportional abundance and measures the probability that two individuals randomly selected from a sample will belong to the same species. 1998) was developed from information theory and is based on measuring uncertainty. bJA�$��pk!l��C��l���s�Ha�#!R9�B3����D9�abg@;�v+]f#p�p����x��ϴ���x��V�~�-&阶��������r��K8�5I�x�h��.��iF���~�Y\�����}��f�����_/F�"�>�tFٴȋ�Sz�=��b�|���S�{����� �>��=N$疶;罬��fL���*�b���YiـjIz1N��Ћٴh�f? •ni = # of individuals (or biomass) in the ith species. :��܁�-�ɼ($((֓(l��� y)��|^�.
H��V�n�F}�W�#UD��q/@ ���R�0�>�~�%�V��D%��gf�"�K�mX\��Μ9�{��b2�m7�r��۷��m[.o�\̋�.�Es� Using the inverse, the value of this index starts with 1 as the lowest possible figure.
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It is computed as: $$H' = -\sum^R_{i=1} ln(p_i) = ln (\frac {1}{\prod^R_{i=1} p^{p_i}_i})$$. If we use the compliment to Simpson’s D, the value is: This version of the index has values ranging from 0 to 1, but now, the greater the value, the greater the diversity of your sample. j. Simpson’s Index (8) - i.
8 is a measure of dominance therefore, (1-8) measures species diversity ii.
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In other words, we need to understand the diversity of organisms present in the community and appreciate the impact our management practices will have on this system. The Shannon-Weiner index is most sensitive to the number of species in a sample, so it is usually considered to be biased toward measuring species richness.
The Shannon-Weiner index (Barnes et al. 253 0 obj
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Resource managers must be cognizant of the effect management practices have on plant and wildlife communities.
where N is the total number of species and ni is the number of individuals in species i. The degree of uncertainty of predicting the species of a random sample is related to the diversity of a community. It is very important to clearly state which version of Simpson’s D you are using when comparing diversity. The width of a single strip (that you are estimating the area for arithmetically) for a Simpson approximation (with the same number of sample points) will be TWICE the width of the Riemann strip.
For example, communities with a large number of species that are evenly distributed are the most diverse and communities with few species that are dominated by one species are the least diverse. %PDF-1.5
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The value of will always fall between 0 and 1, where 1 represents complete diversity and 0 represents complete uniformity.
v. Advantages and Disadvantages: (1) Relatively easy to calculate (2) Fairly sensitive to actual site differences (3) There are several instances where H’ is similar between sites even though sites are different. endstream
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As forest and natural resource managers, we must be aware of how our timber management practices impact the biological communities in which they occur.
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Species richness, as a measure on its own, does not take into account the number of individuals of each species present.
Example \(\PageIndex{3}\):Calculating Shannon-Weiner Index.
The value of Simpson’s D ranges from 0 to 1, with 0 representing infinite diversity and 1 representing no diversity, so the larger the value of \(D\), the lower the diversity. ��b`����7�=�YQ������=�������쨎��7�)M��$�p�@\����H3q�1��@��* �A.~
We want to compute Simpson’s \(D\) for this hypothetical community with three species. •D= Value of Simpson’s diversity index. n�ـ6UC�f�/�m�+�6�6����(s�(��j�o. Biological communities vary in the number of species they contain (richness) and relative abundance of these species (evenness).
Since the mean of the proportional abundance of the species increases with decreasing number of species and increasing abundance of the most abundant species, the value of D obtains small values in data sets of high diversity and large values in data sets with low diversity.
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The higher the value of this inverse index the greater the diversity. However, the first sample has more evenness than the second.
For Location A: = 1 - 608 = 1 - 608 = 1 – 0.337 = 0.663 43 x 42 1806 .
STEP Prep Thread 2021 MAT Prep Thread 2020 The Current Year 11 Chat Thread (2020-2021) A-level Autumn Resits 2020 MEGATHREAD! Unless otherwise noted, LibreTexts content is licensed by CC BY-NC-SA 3.0. So how do we develop a plan that will encompass multiple land use objectives? The key component to habitat for most wildlife is vegetation, which provides food and structural cover. �TFK1v40w4�D����qw
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Landowners, both public an(18)}{d private, often require management of non-timber components, such as wildlife, along with meeting the financial objectives achieved through timber management.
h��Xێ�6}�W�Q.֬xӥ(��l�hqЇ�Z�vؒW��n�#�ޞ! In the second sample, most of the individuals are sugar maples with fewer beech and yellow birch trees.
Then compute the index using the number of individuals for each species: $$D = \sum^R_{i=1} (\dfrac {n_i(n_i-1)}{N(N-1)}) = (\frac {35(34)}{65(64)} +\frac {19(18)}{65(64)} + \frac {11(10)}{65(64)}) = 0.3947$$. endstream
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This is because the Simpson rule essentially requires twice as many test points since it needs a mid point as WELL as the two end points (for each strip). 76 0 obj
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If a community has low diversity (dominated by one species), the uncertainty of prediction is low; a randomly sampled species is most likely going to be the dominant species. Thus a single yellow birch has as much influence on the richness of an area as 100 sugar maple trees. The number of individuals is more evenly distributed between the three species. The LibreTexts libraries are Powered by MindTouch® and are supported by the Department of Education Open Textbook Pilot Project, the UC Davis Office of the Provost, the UC Davis Library, the California State University Affordable Learning Solutions Program, and Merlot. ?�c�ކ��M7�e�@�}%�4��]@��B�FjۨIގ��f�X^�F���1�P �R@��Q#�>�4Z��� t�Ё�cNJ}�)�� �:���x�,+�� ��m�H�=B�@Q@��0`��a@�@� This compliment represents the probability that two individuals randomly selected from a sample will belong to different species. A silvicultural prescription is going to influence not only the timber we are growing but also the plant and wildlife communities that inhabit these stands. Let’s look at an example.
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An equivalent and computationally easier formula is: $$H' = \frac {N ln \ N -\sum (n_i ln \ n_i)}{N}$$.
The more unequal the abundance of species, the larger the weighted geometric mean of the pi values, the smaller the index. Alpha (α) diversity is local diversity, the diversity of a forest stand, a grassland, or a stream. 0
If we use the compliment to Simpson’s D, the value is: $$1-0.3947 = 0.6053$$ This version of the index has values ranging from 0 to 1, but now, the greater the value, the greater the diversity of your sample.
Simpson (1949) developed an index of diversity that is computed as: $$D = \sum^R_{i=1} (\dfrac {n_i(n_i-1)}{N(N-1)})$$.
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alpha, beta, and gamma diversity.
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{4�k�b����p��-�S��N������a�F{E6�N�*�����"���;�J�K�}B�]cI���3�1�@����g���n:����������A�>����_����*=z;�N��IĐ;�V�1m�Pp��#1��pxv6�k���e�F)�,��VaB_�����:A�J�b�?�k��QF+{T��^�%F��f7�&� Diversity Indices - Simpson's Index - Shannon-Weiner Index - Brillouin Index Species Abundance Models Describing Communities There are two important descriptors of a community: 1) its physiognomy (physical structure), as described in the previous lecture, and 2) the number of species present and their relative abundances (species richness and diversity).
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