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.