Transcript PPT: Measuring Biotic Factors

2.5 Investigating Ecosystems
Practical Work
Environmental Systems & Societies
Significant Ideas
The description and investigation of ecosystems
allows for comparisons to be made between
different ecosystems and for them to be
monitored, modelled and evaluated over time,
measuring both natural changes and human
impacts.
 Ecosystems can be better understood through
the investigation and quantification of their
components.

Knowledge & Understandings
1)
2)
3)
4)
5)
The study of an ecosystem requires that it be named
and located ex: Sundarban’s, Bangladesh, a
Mangrove forest along the South-western coastline of
Bangladesh
Organisms in named and located an ecosystem can
be identified using a variety of tools including
dichotomous keys, comparisons to herbarium/
specimen collections, technologies and scientific
expertise.
Sampling strategies may be used to measure biotic
and abiotic factors and their change in space, along
an environmental gradient, over time, through
succession or before and after a human impact, for
example as part of an EIA.
Measurements should be repeated to increase
reliability of data. The number of repetitions required
depends on the factor being measured.
Methods for estimating the biomass and energy of
trophic levels in a community include measurement of
dry mass, controlled combustion, and extrapolation
from samples. Data from these methods can be used
to construct ecological pyramids.
Knowledge & Understandings
6)
7)
8)
9)
Methods for estimating the abundance of non-motile
organisms include the use of quadrats for making
actual counts, measuring population density,
percentage coverage, and percentage frequency.
Direct and indirect methods for estimating the
abundance of motile organisms can be described and
evaluated. Direct methods include actual counts and
sampling. Indirect methods include the use of capturemark-recapture with the application of the Lincoln
Index.
Species richness is the number of species in a
community and is a useful comparative measure.
Species diversity is a function of the number of species
and their relative abundance and can be compared
using an index. There are many versions of diversity
indices but students are only expected to be able to
apply and evaluate the results of the Simpson Diversity
Index. Using its formula, the higher the result, the
greater the species diversity. This indication of diversity
is only useful when comparing two similar habitats or
the same habitat over time.
Application & Skills
1)
2)
3)
4)
5)
6)
7)
8)
9)
Design and carry out ecological investigations.
Construct simple identification keys for up to eight
species.
Evaluate sampling strategies.
Evaluate methods to measure at least three
abiotic factors in an ecosystem.
Evaluate methods to investigate the change
along an environmental gradient and the effect
of a human impact in an ecosystem.
Evaluate methods for estimating biomass at
different trophic levels in an ecosystem.
Evaluate methods for measuring/estimating
populations of motile and non-motile organisms.
Calculate and interpret data for species richness
and diversity
Draw graphs to illustrate species diversity in a
community over time or between communities.
IB Animal Experimentation Policy

You may not perform an experimentation using
animals that involves:
◦ Pain, undue stress, damage to health of animal
◦ Death of animal
◦ Drug intake or dietary change beyond those easily
tolerated by the animal

Consider:
◦ Using cells, plants or simulations instead
If using humans you MUST have written
permission
 AISD safety contracts apply at ALL times during
ALL labs
 No experiments may be done that have any
risk of transferring blood-borne pathogens

K2:
Dichotomous Keys
Method of identifying an organism
 Dichotomous = divided in two parts
 Numbered series of pairs of descriptors
 One matches the species, the other is clearly
wrong
 Each pair leads to another pair of descriptors
OR to an identification
 Features chosen for descriptors should be
easily visible and observable

K2:
Dichotomous
Keys
http://gottalovebio.wikispaces.com/file/view/candy_class._key.jpg/162207257/candy_class._key.jpg
http://www.field-studies-council.org/publications/resources/ks3/images/Liqorice-key.jpg
K2: Practice
 Salamander
 Shark
Keying
Keying
 Look at identification book
examples and large dichotomous
keys on the front table
A2: Creating Dichotomous Keys
• As a group, create a dichotomous key for your bag
of hardware store items.
• REMEMBER:
• There are always only 2 choices (1a or 1b)
• You may start with a branching diagram but this
must be turned into a outline form for final
draft
• It is easiest to start by grouping all objects into 2
groups, then take one group and divide into 2
again until you get to individual items.
• Traits should be used that ANYONE would be
able to observe and come to the same
conclusion
• When naming your organisms they should have
a Genus species name
A2: HOMEWORK
Complete your own dichotomous key of the
creatures (sent by email)
 Email me a copy of your dichotomous key and
make an answer key on the second page.
 Your key will be assessed by your peers, we will
exchange keys and see if they work.

COLLECTING DATA - Where?
When collecting environmental data, it is
almost impossible to collect every possible data
point
 We use sampling methods to make estimations
 These methods enable us to get a random
sample from an entire ecosystem and then use
extrapolation to make estimates and
predictions
 In order to avoid bias it is important that these
methods are truly random.
 Two methods used in ecology to determine
where to collect a sample are quadrats and
transects.

Assumptions Made When Sampling
 The
sample is representative of the
whole system
 It is necessary to take enough samples
so that an accurate representation is
obtained
 It is important to avoid bias when
sampling
Common Sampling Methods
 Abundance
of Non-motile Organisms
◦ Transects and Quadrants
 Abundance of Motile Organism
◦ Actual Count (very difficult if large system)
◦ Lincoln Index
 Capture – Mark - Recapture
 Species Diversity
◦ Simpson Diversity Index
 For comparing 2 habitats or the change in
one habitat over time
TRANSECTS
 Samples
taken at fixed intervals
 Set up along an environmental gradient
(e.g. high to low on a mountain, from
shoreline)
Line Transects
A measured line is randomly placed across the area
in the direction of an environmental gradient
 All species touching the line are recorded along
the whole length of the line or at specific points
along the line
 Measures presence or absence of species

Belt Transects
Transect line is laid out and a quadrant is placed at
each survey interval
 Samples are identified and abundance is estimated
◦ Slow moving animals (limpets, barnacles, snails)
are collected, identified then released
◦ For plants an percent coverage is estimated
 Data collection should be completed by one
individual as estimates can vary person to person

Measuring Non-motile Organisms
 Square
Quadrat – for population density
 Size of quadrat determined by size of
organism being sampled
(10 x 10 cm = 0.01 m2; 0.5 x 0.5m = 0.25 m2,
1.0 x1.0 m = 1 m2 or 5.0 x5.0 m = 25 m2)
 Count all individuals within a randomly
placed quadrat
 Population density is expressed as
number of individuals per square meter
 The larger the size and larger the sample
the more accurate the results
Quadrats
Species Distribution: Population Density
SQUARE QUADRAT
10 cm
10 cm
Find the population density
 Determine the size of the
quadrat (in m2)
◦ 10 cm x 10 cm = 100 cm2 = 0.01 m2
 Count
all individuals IN quadrat
◦ 22
 Calculate
population density
number of individuals per square
meter
22 𝑓𝑙𝑜𝑤𝑒𝑟𝑠

0.01 𝑚2
= 2200 𝑓𝑙𝑜𝑤𝑒𝑟𝑠 𝑝𝑒𝑟 𝑠𝑞. 𝑚.
Grid Quadrat
 Grid
Quadrat
◦ Measures percent frequency – the
% of quadrats in which the species
is found
OR
◦ Measures percent coverage –the
% of area within a quadrat
covered by a single species
◦ NOTE: When you are looking at
one species at a time
 If not using a 10 x 10, you must turn
into a percentage (squares
covered/total # of squares)
Percent Frequency
 Find
the percent frequency
 Count number of squares with
flowers
◦ 15 (note one square has 2 flowers)
 Count
total number of squares
◦ 36
 Calculate
15

36
percentage
× 100 = 42%
http://www.slideshare.net/nirmalajosephine1/biology-form-4-chapter-8dynamic-ecosystem-part-3-42839437
Percent Coverage
 Find
𝑐𝑜𝑣𝑒𝑟𝑒𝑑
%=
× 100
𝑡𝑜𝑡𝑎𝑙 𝑠𝑞𝑢𝑎𝑟𝑒𝑠
24
=
× 100 = 24%
100
1m
18
1m
the percent coverage
 Count full squares
 Now combine pieces to
make full squares
 Calculate percentage
coverage
14 22
24 24 1 2 14
15 3 4 15
17 21 23
19 20 12
13 13 17 18
5 6 12
16 7 8 9 10 11 22
16 19 21 23 20 12
How choose quadrat size?
Think about the size of the organism.
 Think about the area of the system.
 The smaller the quadrat the more accurate,
however the smaller the sample size
 Larger quadrats increase inaccuracy but allow
for broader sample of an area

How many samples?
Obviously the more samples you collect, the
more accurate your estimates for the entire
ecosystem.
 Generally collect enough quadrats that the
number of species collected levels out

Time to Practice

Using Quadrats in Lab find the:
◦ Population Density
◦ Percent Frequency
◦ Percent Coverage
Estimating Percentage Coverage with
Quadrats Wkst
 Random Sampling Lab

Measuring Biomass
Get a sample of the organisms, dry them out
completely in a dehydrating oven (to remove
all water!), find the mass and extrapolate :
 If you collect 10 plants, dry them out and find
their average dry biomass to be 20g, what
would the biomass of a population of 2500
plants be?
 50,000g
 Remember – biomass can be used to create
pyramids of biomass when looking at energy
transfers and is needed for many productivity
calculations!

Measuring abundance of Mobile
Organisms
If the organism is mobile we use a method
called the capture-mark-recapture method
 We then use this data to calculate the Lincoln
Index

𝑛1 × 𝑛2
𝐿𝑖𝑛𝑐𝑜𝑙𝑛 𝐼𝑛𝑑𝑒𝑥 =
𝑛𝑚
𝑛1 = 𝑛𝑢𝑚𝑏𝑒𝑟 𝑐𝑎𝑢𝑔ℎ𝑡 𝑓𝑖𝑟𝑠𝑡 𝑠𝑎𝑚𝑝𝑙𝑒
𝑛2 = 𝑛𝑢𝑚𝑏𝑒𝑟 𝑐𝑎𝑢𝑔ℎ𝑡 𝑠𝑒𝑐𝑜𝑛𝑑 𝑠𝑎𝑚𝑝𝑙𝑒
𝑛𝑚 = 𝑛𝑢𝑚𝑏𝑒𝑟 𝑚𝑎𝑟𝑘𝑒𝑑 𝑜𝑛 𝑠𝑒𝑐𝑜𝑛𝑑 𝑠𝑎𝑚𝑝𝑙𝑒
How to Capture Motile Organisms
REMEMBER: IB Animal Experimentation Policy
 Pitfall Traps
 Small Mammal Traps
 Tullgren Funnels (invertebrates)
 Kick Net
Capture – Mark – Recapture
Capture organisms and count
 Mark organisms with non-toxic, semipermanent, substance that will not increase
the likelihood of harm to the organism
 Release organism back into environment
 The time before you do another capture will
depend on; the mobility of the organism, r or K
strategists

Assumptions
The population of organisms must be closed,
no immigration or emigration.
 The time between samples must be small
compared to the life span of the organism
 The marked organisms must mix completely
with the rest of the population during the time
between sampling.

Using Lincoln Index

In a woodland, the undergrowth was sampled
for snails and 430 were found and marked.
They were then released and the population
similarly sampled after a two-week period. This
second sampling produced 410 snails, 100 of
which were marked.
n1 = 430
 n2 = 410
 m2 = 100


N = 430 x 410 = 1763 snails
100
Using Lincoln Index

While studying field voles, an ecologist
caught 500 and ringed a foot of each before
releasing them. Every day for the next two
weeks he examined the waste material
found in the nests of their predators. He
collected a total of 300 field vole skulls and
15 rings.
How many field voles were
probably in the area examined?


N = 300 x 500 = 10,000
15
Your Turn
Use the Lincoln Index to monitor
this mountain gorilla population
over time:
Year 2003
n1
23
n2
25
nm
18
2004
26
30
22
2005
27
35
21
2006
16
18
15
2007
18
19
16
2008
17
24
17
P
Gorilla hunting is illegal in some regions and carefully controlled
in others, though there is a high demand for illegal bush-meat.
•Deduce between which two years illegal hunters were
active in the forest.
•Explain the long recovery time for the population.
Some Possible Sources of Error with
Capture – Mark – Recapture
Emigration & Immigration
 Natural disaster or disturbance between
captures
 Trap happy or trap shy individuals
 Organisms did not have enough time to
disperse back into ecosystem
 Animals lost marks between recapture

LAB: Capture-Mark-Recapture &
Lincoln Index (Beans & Rice)
Species Diversity
The two main factors taken into account when
measuring species diversity
1. Richness
 A measure of the number of different species
present in a particular area.
 The more species present in a sample, the 'richer'
the sample.
 Takes no account of the number of individuals of
each species present. It gives as much weight to
those species which have very few individuals as
to those which have many individuals.
2. Relative Abundance
 The relative number of individuals of each species
present
http://www.countrysideinfo.co.uk/simpsons.htm
Simpson’s Diversity Index
D= N(N-1)
∑n(n-1)
D = diversity index
 N = total number of organisms of all species found
 n = number of individuals of a particular species

You are not required to memorize this formula but must know
the meaning of the symbols.
Analyzing Simpson’s Index
Used to compare 2 different ecosystems or to
monitor an ecosystem over time
 D values have no units and are used as
comparison to each other
 High D Value Indicates:
◦ Stable and ancient site
◦ More diversity
◦ Healthy habitat
 Low D Value Indicates:
◦ Dominance by one species
◦ Environmental stress
 Pollution, colonization, agriculture

Using Simpson’s Index:
Numbers of individuals (n)
Flower Species
Sample 1
Sample 2
Daisy
300
20
Dandelion
335
49
Buttercup
365
931
Total (N)
1000
1000
Find the diversity index for sample 1:
𝑁(𝑁 − 1)
𝐷=
𝑛(𝑛 − 1)
𝐷=
1000(999)
300∙299 + 335∙334 +(365∙364)
𝐷 = 2.99
Using Simpson’s Index:
Numbers of individuals (n)
Flower Species
Sample 1
Sample 2
Daisy
300
20
Dandelion
335
49
Buttercup
365
931
Total (N)
1000
1000
Now, find the diversity index for sample 2:
𝑁(𝑁 − 1)
𝐷=
𝑛(𝑛 − 1)
𝐷=
1000(999)
20∙19 + 49∙48 +(931∙930)
𝐷 = 1.15
Sample 1 has a higher Simpson’s Biodiversity
index than Sample 2 even though it has the
same number of species present and the
same number of total individuals because
there is more even distribution of the
organisms through the species.
YOUR TURN
The insects in two meadows are being
investigated. The following data was collected.
Compare the diversity of the two meadows
Organism
Orthoptera
(grasshopper)
Orthoptera
(grasshopper)
Lepidoptera
(butterfly)
Lepidoptera
(butterfly)
Coleoptera
(beetle)
Hymenoptera
(wasp)
Hymenoptera
(wasp)
Hymenoptera
(bee)
Description
Green with
red legs
Brown with
yellow stripe.
Large, blue
Small, blue
Red & Blue
Black
Purple
Striped
Meadow 1
Meadow 2
16
5
26
3
12
25
2
17
9
12
4
5
YOUR TURN Solution
Organism
Orthoptera
(grasshopper)
Orthoptera
(grasshopper)
Lepidoptera
(butterfly)
Lepidoptera
(butterfly)
Coleoptera (beetle)
Hymenoptera
(wasp)
Hymenoptera
(wasp)
Hymenoptera (bee)
Description
Green with red
legs
Brown with
yellow stripe.
Large, blue
Meadow 1
16
Meadow 2
25
5
2
26
17
Small, blue
3
9
Red & Blue
Black
12
12
Purple
4
Striped
5
62(61)
3782
𝐷1 =
=
= 3.6
16 ∙ 15 + 5 ∙ 4 + 26 ∙ 25 + 3 ∙ 2 + (12 ∙ 11) 1048
𝐷2 =
74(73)
25 ∙ 24 + 2 ∙ 1 + 17 ∙ 16 + 9 ∙ 8 + 12 ∙ 11 + 4 ∙ 3 + (5 ∙ 4)
5402
=
= 4.9
1110
Simpson’s Index
Lab
activity with playing cards
Simpson’s Diversity Homework
Questions