16 - Dr. Mark Pyron
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Transcript 16 - Dr. Mark Pyron
SPECIES ABUNDANCE AND DIVERSITY
Chapter 16
Molles: Ecology 2nd Ed.
TWS
Thu 7:15 pm
CL 230
Turtles, squirrels, and dead birds
Dr. Travis Ryan
Butler University
Molles: Ecology 2nd Ed.
Inqsit exam starts Thu
Short answer version
Multiple choice version
Molles: Ecology 2nd Ed.
Objectives
•
Define “ecological community” and describe
major characteristics.
•
Quantify species abundance and species
diversity.
•
Describe the processes that determine
species diversity of communities.
•
Explain how environmental factors influence
species diversity.
Molles: Ecology 2nd Ed.
Community
•
An association of interacting species
that occurs in defined area.
•
Interactions include competition,
exploitation, and mutualism.
•
Entire community, bird community,
plant community, insect community….
Molles: Ecology 2nd Ed.
Community Characteristics and Processes
Species
Immigration
Species Composition
-
Number of species
Relative abundance
Speciation
Species
Emigration
Extinction
Community Structure
(Height, Layers)
Species Diversity
Quantifying Species Abundance
•
Abundance: The actual number of organisms
of a species per unit of area or volume
(Density).
•
Relative Abundance: The proportion or
percentage of all organisms in a community or
sample that are a particular species.
RA = # of species A / total # organisms
Example:
A representative sample of 500 stream invertebrates is
collected:
Species
Abundance
Relative
Abundance
Clam
24
0.048
(= 24/500)
Snail
18
0.036
(= 18/500)
Mayfly larvae
11
0.022
Caddisfly larvae
41
0.082
Dragonfly Larvae
8
0.016
Midge larvae
203
0.406
Worm
150
0.300
Leech
45
0.090
Total
500
1.000
Species Abundance
•
How common are most species?
•
There are regularities in relative abundance
of species in communities in all ecosystems
•
Preston developed concept of:
Distribution of commonness and rarity
Molles: Ecology 2nd Ed.
Log-Normal Pattern of Species
Abundance In Communities
Very few species have extremely
high relative abundance
Why ?
Very few species have extremely
low relative abundance
Most species are moderately
abundant
Plants
Birds
Low
Abundance
(Log Scale)
High
Species Diversity
Two factors define species diversity:
Species Richness:
Number of species in community
Species Evenness:
Relative abundance of species
Molles: Ecology 2nd Ed.
Both have 5 species = same species richness
Fig 16.5
Molles: Ecology 2nd Ed.
Quantitative Index of Species Diversity
•
Shannon-Wiener Index:
s
H’ = - pi logepi
i=l
H’
pi
loge
s
= Shannon-Wiener diversity index
= proportion of the ith species
= natural logarithm of pi.
= number of species in community
Molles: Ecology 2nd Ed.
H’ example
•
Community:
AAAAAAAAAA
AAAAAAAAAA
AAAAAAAAAA
AAAAAAAAAA
AAAABCDEFG
•
Sum values across all species
pi = 44/50 = 0.88, pi = 1/50 = 0.02
Calculate ln for each (ln 0.88 = - 0.128)
•
•
Molles: Ecology 2nd Ed.
S=7
H’
•
•
•
Sum pi’s
= 0.88 (-0.128) + 0.02 (- 3.91) +0.02 (- 3.91)
+ 0.02 (- 3.91) + 0.02 (- 3.91) + 0.02 (- 3.91)
+ 0.02 (- 3.91) = - 0.58
Change sign; H’ = 0.58
Molles: Ecology 2nd Ed.
Another example:
•
•
Community:
ABCDEABCDE
ABCDEABCDE
ABCDEABCDE
ABCDEABCDE
ABCDEABCDE
H’ = 1.61
Molles: Ecology 2nd Ed.
S=5
What’s the purpose of H’?
•
Includes both species richness and
evenness
Molles: Ecology 2nd Ed.
Rank Abundance Curves
•
Relative abundance and species diversity in
community: plot relative abundance of
species and rank abundance
Fig 16.8
Molles: Ecology 2nd Ed.
Environmental Complexity
Species diversity increases with environmental
complexity
MacArthur: warbler diversity increased =
vegetation stature increased
Env. complexity = foliage height
Many find positive relationship between env.
complexity and species diversity
Molles: Ecology 2nd Ed.
Fig 16.9
Molles: Ecology 2nd Ed.
Algal and Plant Species Diversity And
Increased Nutrient Availability
•
•
Repeatedly observed negative relationship
between nutrient availability and algal and
plant species diversity
Adding nutrients to water or soils reduces
diversity of plants and algae
Reduces number of limiting nutrients
Molles: Ecology 2nd Ed.
Disturbance and Diversity
•
Disturbance difficult to define because it
involves departure from “average conditions.”
Average conditions may involve substantial
variation
Molles: Ecology 2nd Ed.
Sousa defined disturbance:
•
Discrete, punctuated, killing, displacement,
or damaging of one or more individuals that
directly or indirectly creates an opportunity
for new individuals to be established
Molles: Ecology 2nd Ed.
Disturbance and Diversity
•
Another definition of disturbance:
Any relatively discrete event in time that
disrupts ecosystem, community, or
population structure and changes
resources, substrate availability, or the
physical environment
Molles: Ecology 2nd Ed.
Two major characteristics of disturbance:
Frequency
Intensity
Molles: Ecology 2nd Ed.
�Intermediate Disturbance Hypothesis
�
�
Connell
disturbance is a prevalent feature that
significantly influences community diversity
Proposed that both high and low levels of
disturbance reduce diversity
Intermediate levels promote higher
diversity
Molles: Ecology 2nd Ed.
•
Sufficient time between disturbances allows
wide variety of species to colonize, but not
long enough to allow competitive exclusion
Molles: Ecology 2nd Ed.
Disturbance and Diversity in The Intertidal Zone
•
Sousa studied effects of disturbance on
diversity of algae and invertebrates growing on
boulders in the intertidal zone
Predicted level of disturbance depends on
boulder size
Molles: Ecology 2nd Ed.
Large boulders move less = heavier
Boulders with highest diversity of species
had intermediate levels of disturbance
Fig 16.18
Molles: Ecology 2nd Ed.
Disturbance and Diversity in
Temperate Grasslands - burrowing as a
disturbance
•
•
Whicker and Detling
prairie dogs (Cynomys spp.)
source of disturbance on N. A.
prairies
Build extensive burrow
systems
Move 200-225 kg soil from
underground to entrance
Molles: Ecology 2nd Ed.
•
They removed vegetation around burrows
Area opens to colonization
Pest control programs reduced prairie
dog populations 98%
Eliminated dynamic
influences on plant
communities
Molles: Ecology 2nd Ed.
Summary
•
•
•
•
Most species are moderately abundant; few
are very abundant or extremely rare
A combination of the number of species and
their relative abundance defines species
diversity
Species diversity is higher in complex
environments
Intermediate levels of disturbance promote
higher diversity
Molles: Ecology 2nd Ed.
Molles: Ecology 2nd Ed.