How to Calculate Biodiversity
 The question of how many different species exist in a particular environment is central to the
understanding of why it is important to promote and preserve species diversity.
 A uniform population of a single species is more at risk if environmental changes occur in an
area.
 A more diverse community consisting of many different species has a better chance of
containing individuals that are able to adapt if environmental changes occur in an area.
METHOD #1: BIODIVERSITY INDEX
 Scientists use a formula called the biodiversity index to represent the species diversity in a given
area.
 A simple biodiversity index is calculated using the following formula:
biodiversity index (B.I.) =
number of species in the square area (numerator)
total number of individuals in the area (denominator )
 Biodiversity index ranges from 0 – 1.
 The closer the biodiversity index is to 1 the higher the biodiversity.
 The closer the biodiversity index is to 0 the lower the biodiversity.
Examples - Calculation of Biodiversity Index
#1. A 4 X 4 square meter area in a carrot patch has 300 carrot plants, all the same species.
1 species, 300 organisms
B.I. = ?
B.I. = # of species
# of organisms
B.I. = 1_ = 0.00333
300
The answer is closer to zero than one so it has a low biodiversity.
#2. A 4 X 4 meter square area in the forest has 1 pine tree, 1 fern, 1 conifer tree, 1 moss, and 1 lichen.
5 species, 5 organisms
B.I. = ?
B.I. = # of species
# of organisms
B.I. = 5_ = 1
5
The answer is closer to one than zero so it has a high biodiversity.
METHOD #2: SPECIES RICHNESS
 One way to measure biodiversity is to simply count the number of different species at a site.
 This number gives a scientist the measurement of “species richness.” By comparing species
richness at two different sites, scientists learn something about biodiversity.
 However, a simple count of species richness does not necessarily give scientists a complete
picture of the biodiversity in an ecosystem.
 This does not mean that the number of species in an ecosystem is not important, but it is only
one part of the equation.
 When measuring biodiversity in an ecosystem, other patterns must be taken into account........
METHOD #3: RELATIVE ABUNDANCE
 The term “relative abundance” is used by ecologists to describe the number of individuals of a
species relative to the total number of individuals in an area.
 Identifies the percentage (or proportion) of each species represented in the area.
Example - Species Richness and Relative Abundance
Calculate the following for data gathered from the schoolyard:
i)
relative abundance
ii)
species richness tree census
Table 1: Tree Census Data for the Oakville Trafalgar Schoolyard Ecosystem
Tree Species
# of
individuals
sp #1
sp #2
sp #3
sp #4
sp #5
Total
26
32
45
18
39
160
i) relative
abundance
26/160
32/160
45/160
18/160
39/160
160/160
= 0.16
16%
ii) species
richness
or
= 0.20
20%
or
=0.28 or
= 0.11
28%
11%
5
or
= 0.24
24%
or
=1
or
100%