Download Simpson*s Diversity Index

G4: Conservation of Biodiversity…
G.4.1: ‘Explain the use of biotic indices
and indicator species in monitoring
environmental change’
Biological monitoring and indicator
species
What is an indicator species?
Any biological species that defines a trait or
characteristic of the environment:
– May indicatethe ‘viability’ of a particular ecosystem
– May indicate a disease outbreak
– May indicate pollution
– May indicate species competition
– May indicate climate change
Well-known indicator species…
• Plants – mosses and lichens
• Macroinvertebrates: Stoneflies
• Mollusca: mussels
Advantages of Biological Monitoring
1. We can detect intermittent pollution
2. A specific change in the Biotic index can
indicate a specific type of pollutant
3. Food chains can accumulate pollutants
(biomagnification) – particularly in higher
trophic levels
Disadvantages of Biological Monitoring
• Distribution of organisms may be patchy so
sampling must be done carefully
• Invertebrate organisms tend to be seasonal
• Some indicator species show tolerance to
different pollutants
Biological Monitoring is frequently
used to evaluate marine or aquatic
pollution
• Oysters and mussels are used as indicator
species (‘bio-monitors’) to assess
environmental pollution of coastal waters
• Mussel Watch!
Indicator species can be monitored to
indicate an increase OR decline in
biodiversity
• ‘Sentinel Species’
• ‘Keystone species’
Keystone species
• These are species which
have a disproportionately
significant effect on their
environment
• Sometimes they are
predators
• Sometimes they are
‘ecological engineers’
• Examples: Grizzly Bear,
Sea Otters, Sea Stars
Biological Monitoring is frequently
used to identify pollution or presence
of toxins on land
• On land, lichens are often used as indicator
species since they are sensitive to sulphur
dioxide
• ‘Bushy’ lichens need pristine air
• Leafy lichens can survive a small amount of
pollution
• ‘Crusty’ lichens can survive in heavily polluted
air
• Regions devoid of lichens may indicate a high
concentration of sulphur dioxide
A Reminder from G3: Simpson’s
Diversity Index…
G.3.1: Calculate the Simpson diversity index
for two local communities
G.3.2: Analyze the biodiversity of the two
local communities using the Simpson index
Simpson’s Diversity Index
Is an estimate of DIVERSITY
It estimates RICHNESS and
‘EVEN-NESS’ of an ecosystem
What is the usefulness of a Diversity
Index?
 It provides information about
‘rarity’ and ‘common-ness’ of
species in a community
 Diversity indices allow us to
monitor diversity over time in
changing ecosystems – for
example, to monitor effects of
pollution or climate change
 Diversity indices allow us to
compare communities
 Diversity indices convert many
species into a single number
Limitations!
Simpson’s Diversity Index
is more sensitive for
common species
(abundant) and LESS
sensitive for RARE
species…
So what is ‘species richness’
• Indicates species diversity…but
• Estimating ‘richness’ alone would provide only a
limited description of a community: it would not tell
us anything about relative abundance of the species
identified…
For example…
Why is it important to evaluate
‘species even-ness’?
Even-ness: A measure of the relative abundance
of species making up the community
The relevance of ‘species even-ness’
Examples of Simpson’s Reciprocal Index
1. Equal diversity of species
Examples of Simpson’s Reciprocal Index
2. Low species diversity: Domination of a single particular
species…
Example 3 of Simpson’s Reciprocal Index
Only one species is present
Example 3 of Simpson’s Reciprocal Index
Very few individuals of certain species are present