Transcript Species richness - Michigan State University

Species richness
The number of species is an important biological
variable that scientists try to quantify
Species diversity
The number of species weighted by their
abundance.
For example, a forest with 10 tree species, each
with ten individuals, is generally considered
more diverse than a forest with 10 tree
species, one of which is represented by 91
individuals with the other 9 species only
represented by one individual each.
To estimate species richness one must first
sample an area(s)
Sampling is measuring a small part of an entity
assuming that this small part is representative
of the larger entity
Ways to diminish biases in sampling
Use multiple sampling techniques
Sample at random locations (each location has
an equal opportunity of being sampled--in
other words, sampling should not be biased in
favor of some locations and against other
locations)
Sample repeatedly
In addition to sampling correctly, it is important
to recognize that not all species are equally
detectable
In addition, species may vary in their
detectability across habitat types
Generally, the number of species detected
(observed) through sampling, is not the best
estimate of the species richness of an area
Ways to look at patterns and estimate
diversity after sampling is completed
Diversity indices
Accumulation curves/Rarefaction curves
Using species abundance distribution data
Shannon Diversity Index
Also known as the Shannon-Wiener or ShannonWeaver. This index uses species abundances
to calculate an index of diversity
H = -Σ pi ln(pi)
pi= proportion of the ith species
Imagine the following are the abundances of
individuals in a community of frogs detected
by a biologist
Species 1 = 15
Species 2 = 10
Species 3 = 3
Species 4 = 1
H = -Σ pi ln(pi)
15+10+3+1 = number of individuals in the
community
p1 = 15/29, p2 = 10/29, p3=3/29, p4=1/29
H = -Σ (0.52(ln0.52)+(0.34(ln0.34)+(0.10(ln0.10) +
0.03(ln0.03) = 1.05
1.05 = diversity index, which we compare to other,
similarly calculated diversity indices if we want to
compare the diversities of different communities
Assumption of Shannon Index
All species are equally detectable
This assumption may be more true for some
taxonomic groups than others. In general, for
mobile organisms, the Shannon Index is not a
strong way to estimate diversity
Accumulation curve—”records the total number
of species revealed, during the process of data
collection, as additional individuals (or sample
units) are added to the pool of all previously
observed or collected individuals or samples”
Gotelli, N.J. and R. K. Colwell. 2001. Ecology Letters 4:379-391.
Braulio Carillo
Tabanid fly
Tabanid fly species accumulation curves for La Selva and 1070 m in Braulio Carillo
A Report on the Tabanidae of La Selva Biological Station and 1070m in Braulio Carrillo National Park
Taxonomic Collaborator: John F. Burger, Department of Zoology, Spaulding Hall University of New Hampshire, Durham, New Hampshire 03824 USA.
Page author: John T. Longino, The Evergreen State College, Olympia WA 98505 USA
Accumulation curves show differences in species
richness, given the number of individuals
detected
When these curves reach an asymptote,
sampling may be reasonably complete
Rarefaction curves are produced by “repeatedly
re-sampling the pool of N individuals or N
samples, at random, plotting the average
number of species represented by 1, 2,…N
individuals or samples. Sampling is generally
done without replacement”
Rarefaction curves represent the statistical
expectation for the corresponding
accumulation curve
Black line is accumulation curve, red line is rarefaction curve, dashed lines are confidence
Intervals. Rarefaction curve is based on 100 samples. Data are for bats at site in
Malaysia. http://www.wcsmalaysia.org/analysis/Biod_richness.htm
Williams et al. 2001. Variation in native bee faunas and its implications for detecting community change. Ecology and Society 5:7
If one bases rarefaction curves on numbers of
samples versus individuals, one needs to be
careful
If the density of individuals differs among
samples, results will be misleading
Because each
sample from
second growth
forest has more
individuals than
each sample from
old growth forest,
the samples for the
two types of forest
are not directly
comparable.
Second growth forest
is denser, greater no. of
individuals, so rarefying
with samples gives misleading result that second
growth forest is more
species-rich. Rarefying
with individuals controls
for density differences.
From Gotelli and Colwell 2001.
Another technique for comparing
species richness
Use program Specrich, available at
http://www.mbrpwrc.usgs.gov/software/specrich.html
Patuxent Wildlife Research Center website
Community A Community B
No of spp. detected
with one individual
60
30
No of spp. detected
with two individuals
25
20
No of spp. detected
with three individuals
10
20
No of spp. detected
with four individuals
2
15
No of spp. detected
with five individuals
3
15
Which community do you think has a greater species richness?
Species abundance distribution data (as
presented in the previous slide) are used to
estimate species richness in this method.
Estimated species
richness
Standard error
(interpolated N) of estimate
Range of
estimate
Community A
174.3
14.1
160-188
Community B
130.0
7.7
122-138
Characteristics of particular taxonomic or
ecological groups that are more likely to be
more species-rich than others?
Characteristics of particular environments that
are more likely to be more species-rich than
others?
Planting design-In islands or plantations?
T
6m
18 m
8m
V
T
E
T
I
V
V
V
T
T
V
V
E
T
T
V
V
V
T
V
T
T
E
V
T
T
V
I
V
V
E
T
E
T
V
V
T
T
T
T
V
I
V
T
T
E
T
I
T
V
E
T
E
V
T
I
V
T
T
V
T
V
V
Control
Island
V
E
V
V
V
E
V
T
V
T
T
V
I
V
T
V
Plantation
T
V
V
T
E
T
E
T
V
I
I
I
T
E
E
T
T
E
I
I
E
V
V
V
V
T
E
T
E
I
I
V
T
T
I
I
E
E
E
E
T
V
V
T
I
V
T
V
V
I
I
I
I
V
T
T
E
T
E
E
E
T
T
E
E
E
E
T
V
V
I
V
I
I
I
I
E
I
V
V
I
V
V
V
T
E
T
T
T
T
T
I
E
E
E
T
V
V
T
I
I
T
E
E
T
T
E
I
I
E
V
V
V
V
V
E
I
I
I
I
V
V
I
I
I
I
E
T
T
T
E
T
T
T
T
T
I
E
E
E
T
V
V
T
T
E
T
T
E
E
E
E
I
I
V
I
V
V
V
V
V
E
I
I
I
I
V
V
I
I
I
E
E
T
T
T
T
E
T
T
T
E
T
T
E
E
E
E
I
I
V
I
V
V
V
V
V
E
I
I
I
I
I
V
T
V
T
V
T
T
E
T
T
E
E
E
T
I
I
V
I
V
V
V
V
E
E
T
E
I
I
V
V
V
T
T
I
I
T
T
E
T
T
E
E
E
T
I
I
V
I
V
V
V
V
V
E
I
T
E
T
T
E
E
E
E
T
V
I
I
I
V
T
T
E
E
V
I
I
E
V
T
V
V
I
V
V
V
T
T
E
I
I
T
E
T
I
I
I
V
I
V
E
T
E
8m
6m
V
I
V
I
E
T
T
E
I
V
12 m
V
I
V
T
San Gabriel, April 2007
San Gabriel March 2006
Loma Linda March 2006