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Species Abundance and Diversity
Chapter 16
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Outline
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Introduction
Species Abundance
 Lognormal Distribution
Species Diversity
Environmental Complexity
 Niches
Disturbance and Diversity
 Intermediate Disturbance Hypothesis
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Introduction
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Community: Association of interacting
species inhabiting some defined area.
 Community Structure includes attributes
such as number of species, relative
species abundance, and species diversity.
Guild: Group of organisms that all make their
living in the same fashion.
 Seed eating animals in the desert.
Life Form: Combination of structure and
growth dynamics.
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Species Abundance
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There are regularities in the relative
abundance of species in communities that
hold regardless of the ecosystem.
Preston developed concept of distribution of
commonness and rarity.
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Lognormal Distribution
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Preston graphed abundance of species in
collections as frequency distributions.
 Lognormal Distributions
 Bell-shaped curves.
 In most lognormal distributions, only
portion of bell-shaped curve is
apparent.
– Sample size has large effect.
– Significant effort to capture rare
species.
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Lognormal Distribution
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Lognormal Distribution
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May proposed lognormal distribution is a
statistical expectation.
Sugihara suggested lognormal distribution is
a consequence of the species within a
community subdividing niche space.
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Species Diversity
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Two factors define species diversity:
 Species Richness
 Number of species in the community.
 Species Evenness
 Relative abundance of species.
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Species Diversity
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Quantitative Index of Species Diversity
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Shannon Wiener Index:
s
H’ = -Σpi logepi
i=l
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H’
Pi
Loge
S
= Value of SW diversity index.
= proportion of the ith species.
= natural logarithm of pi.
= Number of species in community.
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H’ example
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Community:
AAAAAAAAAA
AAAAAAAAAA
AAAAAAAAAA
AAAAAAAAAA
AAAABCDEFG
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Sum values across all species
pi = 44/50 = 0.88, pi = 1/50 = 0.02
Calculate ln for each (ln 0.88 = - 0.128)
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S=7
Molles: Ecology 2nd Ed.
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H’
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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.
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Another example:
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Community:
ABCDEABCDE
ABCDEABCDE
ABCDEABCDE
ABCDEABCDE
ABCDEABCDE
S=5
H’ = 1.61
Molles: Ecology 2nd Ed.
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What’s the purpose of H’?
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Includes both species richness and
evenness
Molles: Ecology 2nd Ed.
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Rank Abundance Curves
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Can also portray relative abundance and
species diversity within a community by
plotting relative abundance of species
against their rank in abundance.
 Greater evenness indicated by lower
slope.
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Rank Abundance Curves
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Environmental Complexity
In general, species diversity increases with
environmental complexity or heterogeneity
MacArthur found warbler diversity increased as
vegetation stature increased
Measured env. complexity as foliage height
Many studies find positive relationship between
env. complexity and species diversity
Molles: Ecology 2nd Ed.
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Environmental Complexity
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Fig 16.9
Molles: Ecology 2nd Ed.
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Diversity of Algae and Plants
Hutchinson:
Phytoplankton communities present
paradox – they live in relatively simple
environments and compete for the same
nutrients, yet many species coexist
without competitive exclusion
Env. complexity may account for diversity
Molles: Ecology 2nd Ed.
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•Diversity of Algae and Plants
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Algal niches appear to be defined by nutrient
requirements
 Tilman (1977)
 found coexistence of freshwater diatoms
depended upon ratio of silicate and
phosphate
Molles: Ecology 2nd Ed.
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Tilman (1977) found conditions allowing
coexistence
Diatoms held different trophic niches
Thus different diatoms would dominate
different areas
Trophic niches =
nutrient requirements
Molles: Ecology 2nd Ed.
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Heterogeneity and Diversity of Tropical Forests
• Jordan – Amazon tropical forest diversity
organized in two ways:
 1. Large number of species live within
most tropical forest communities
Fig 16.14
Molles: Ecology 2nd Ed.
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2. Large number of plant communities in a
given area, each with distinctive species
composition
Fig 16.14
Molles: Ecology 2nd Ed.
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Algal and Plant Species Diversity And
Increased Nutrient Availability
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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.
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Disturbance and Diversity
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Disturbance difficult to define because it
involves departure from “average conditions.”
 Average conditions may involve substantial
variation
Molles: Ecology 2nd Ed.
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Sousa defined disturbance:
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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.
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Disturbance and Diversity
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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.
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Two major characteristics of disturbance:
Frequency
Intensity
Molles: Ecology 2nd Ed.
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�Intermediate Disturbance Hypothesis
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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.
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Sufficient time between disturbances allows
wide variety of species to colonize, but not
long enough to allow competitive exclusion
Molles: Ecology 2nd Ed.
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Disturbance and Diversity in The Intertidal Zone
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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.
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Large boulders move less = heavier
Boulders with highest diversity of species
had intermediate levels of disturbance
Fig 16.18
Molles: Ecology 2nd Ed.
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Disturbance and Diversity in
Temperate Grasslands - burrowing as a
disturbance
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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.
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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.
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Review
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Introduction
Species Abundance
 Lognormal Distribution
Species Diversity
Environmental Complexity
 Niches
Disturbance and Diversity
 Intermediate Disturbance Hypothesis
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