Transcript Global Ecology

BIO-201
ECOLOGY
Communities and Ecosystems
H.J.B. Birks
Communities and Ecosystems
1. Species Abundance, Diversity, & Community Ecology
2. Community Ecology and Dynamics
3. Ecosystem Ecology – Energy Flux
4. Ecosystem Ecology – Matter Flux
5. Long-term Ecology (=Ecological Palaeoecology)
6. Broad-scale Ecology – World Vegetation Biomes
7. Broad-scale Ecology – Landscape & Geographical Ecology
8. Broad-scale Ecology – Species Richness Patterns in Time
9. Broad-scale Ecology – Species Richness Patterns in Space
10.Broad-scale Ecology – Global Earth-System Ecology
BIO-201
ECOLOGY
1. Species Abundance,
Diversity, and Community
Ecology
H.J.B. Birks
Species Abundance, Diversity, and
Community Ecology
Sub-divisions of ecology
Scales in ecology
Community level of ecological organisation
Important concepts about community level of organisation
The study of communities
How do we quantify the number & relative abundance of species
in communities? - Species abundances
- Rank-abundance curves
- Species numbers (= richness) and species diversity
- Not all species are equal!
What determines diversity? - Environmental complexity
- Disturbance and diversity
What determines community structure?
Different concepts of the community
How to analyse community-scale data?
Conclusions and summary
Pensum
The lecture, of course,
and
the PowerPoint handouts of this lecture
on the BIO-201 Student Portal
Also ‘Topics to Think About’ on the
Student Portal filed under projects
Topics to Think About
On the Bio-201 Student Portal filed under
Projects, there are several topics to think about
for each lecture. These topics are designed to
help you check that you have understood the
lecture and to identify important topics for
discussion in the Bio-201 colloquia.
In addition, there are two or three more
demanding questions at the sort of level you can
expect in the examination question based on my
10 lectures. These can also be discussed in the
colloquia.
Background Information
There is now a wealth of good or very good ecology
textbooks but perhaps no excellent, complete, or
perfect textbook of ecology.
Not surprising, given just how diverse a subject
ecology is in space and time and all their scales.
This lecture draws on primary research sources, my
own knowledge, experience, observations, and
studies, and several textbooks.
Textbooks that provide useful background
material for this lecture
Begon, M. et al. (2006) Ecology. Blackwell (Chapter 16, parts of
Chapters 19 & 20)
Bush, M. (2003) Ecology of a Changing Planet. Prentice Hall
(Chapter 15)
Krebs, C.J. (2001) Ecology. Benjamin Cummings (Chapters 20,
22, 23)
Miller, G.T. (2004) Living in the Environment. Thomson (Chapter
8)
Molles, M.C. (2007) Ecology Concepts and Applications. McGrawHill (Chapter 16)
Ricklefs, R.E. & Miller, G.L. (2000) Ecology. W.H. Freeman
(Chapters 26, 27, 29)
Smith, R.L. & Smith, T.M. (2007) Ecology and Field Biology.
Benjamin Cummings (Chapter 20)
Townsend, C.R. et al. (2008) Essentials of Ecology. Blackwell
(Chapters 9, 10)
A Reminder
If you try to read Begon, Townsend, and Harper
(2006) Ecology – From Individuals to Ecosystems,
there is a 17-page glossary of the very large (too
large!) number of technical words used in the book
on the Bio-201 Student Portal. It can be
downloaded from the File Storage folder.
Good luck!
Sub-Divisions of Ecology
1. Functional ecology and evolutionary ecology
2. Modern ecology and long-term ecology (=palaeoecology) (the
Fourth dimension of ecology)
3. Autecology – study of ecological relationships of a single
species
4. Synecology – study of all the species living together as a
community (group of plants and animals in a given place
forming ecological units of various sizes and degrees of
interrelation and integration)
5. Pure and applied ecology
"Pure"– understand, for understanding's sake, the processes
responsible for determining the structure and composition of
particular assemblages or communities
"Applied"– ecology relevant to food gathering and production,
conservation, control of pests and pathogens, pollution,
preservation of biodiversity, etc. Includes conservation ecology
and restoration ecology.
6. Descriptive ecology – basic patterns of what grows where, what
are the environmental variables, and what is the inherent
variation in space and time
Explanatory ecology - underlying processes behind observed
patterns. Processes may be proximal (near) or ultimate (final)
Predictive ecology – use ecological knowledge and
understanding to predict how organisms will respond to
environmental changes
7. Observational or field ecology – 'scientific natural history'
Laboratory experimental ecology – 'simplified ecology'
Field experimental ecology – most difficult to do
8. Behavioural ecology – individuals
Population ecology – populations
Community ecology – communities
Landscape ecology – landscapes
Geographical ecology – mappable features
Global ecology – biomes and Earth's systems
Ecology is like a giant and complex jigsaw puzzle
If the organism is not a
predator, 'prey' is
replaced by 'food' or if
the organism is a plant,
'prey' is replaced by
'light and nutrients'.
In addition, an organism
competes with other
organisms (competitors)
for food.
In reality a multi-dimensional (and unsolvable!) jigsaw-puzzle
and we do not have all the pieces!
Scales in Ecology
Biological or hierarchical scales
Biosphere
Biosphere
Biomes e.g. rainforest
landscapes
Ecosystems & Landscapes
Communities
Communities
Species
Populations
Populations; breeding individuals
Individual organisms
Individual
Global Scale (Lectures 6, 10)
Biosphere
Atmosphere
Biosphere
Vegetation and animals
Soil
Crust
Rock
Hydrosphere
core
Lithosphere
(Lithosphere)
Mantle
Crust
Crust
(soil and rock)
Biosphere
(Living and dead
organisms)
Hydrosphere
(water)
Lithosphere
(crust, top of upper mantle)
Atmosphere
(air)
Broad Spatial or Biome Scale (Lecture 6)
World
Vegetation
Types or
Biomes
Coastal chaparral
and scrub
Coastal
mountain
ranges
Role of
climate
15,000 ft
10,000 ft
5,000 ft
Coniferous
forest
Sierra
Nevada
Mountain
Desert
Great
American
Desert
Coniferous
forest
Rocky
Mountains
Prairie
grassland
Deciduous
forest
Mississippi
Great
River Valley
Plains
Appalachian
Mountains
Average annual precipitation
100-125 cm (40-50 in.)
75-100 cm (30-40 in.)
50-75 cm (20-30 in.)
25-50 cm (10-20 in.)
below 25 cm (0-10 in.)
Landscape
Scale
(Lecture 7)
Coastmountain
transition in
western
Norway
Geographical Scale (Lecture 7)
Elevation gradient = gradual change
Alpine
tundra
Montane
coniferous
forest
Deciduous
forest
Temperate
forest
SEA
Community Scale (Lectures 1, 2)
Populations of different species living and interacting
within an ecosystem are referred to collectively as a
community
Often no real
boundaries between
communities
Community Boundaries: Often Gradual
Land zone
Transition zone
Number
of species
Species in land zone
Species in aquatic zone
Species in transition
zone only
Aquatic zone
Deciduous forest and rocky shore = sharp
change between communities
Scales of relevance in these ten lectures on
Communities and Ecosystems
Community scale (Lectures 1, 2)
Ecosystem (Lectures 3, 4), Landscape (Lecture 7),
and Geographical (Lectures 7, 8, 9) scales
Biome scale (Lecture 6)
Biosphere or Global scale (Lecture 10)
plus Time dimension (long-term ecology or
palaeoecology) (Lectures 5, 8)
Spatial and Temporal Scales of
Biodiversity – closely related
Spatial scale
Biological scale
Temporal scale
(years)
Local
Populations,
communities & habitat
patches
1 – 100
Landscape
Between communities
100 – 1000
Regional
Regions, countries
10,000
Continental
Continents
1 – 10 million
Global
Global biodiversity &
biosphere
10 – 100 million
Today’s Ecological Scale
Biosphere
Biosphere
Biosphere
Ecosystems
Biomes
Ecosystems & Landscapes
Communities
COMMUNITIES
Species
Populations
Organisms
Populations
Organisms
Community Level of Ecological
Organisation
'Group of plants and animals in a given place and time
forming ecological units of various sizes and degrees of
inter-relation and integration.'
Community concept first applied to plants, more recently
applied to animals. Most definitions only refer to plants.
'an aggregate of living plants having mutual relations
among themselves and to the environment' (Oosting,
1956)
'a collection of plant populations found in one habitat type
in one area, and integrated to a degree by competition,
complementarity, and dependence' (Grubb, 1987)
Important Concepts about
Community Level of Organisation
1. Collections of species which occur together in some
common environment or habitat type.
2. Organisms making up the community are somehow
integrated and may interact as a unit.
3. Communities are not constructed only of plants.
4. Some communities are mostly animals (e.g. fish and
invertebrates that comprise coral-reef communities).
5. Most communities consist of a mixture of plants, animals,
fungi, prokaryotes, and protoctists.
6. Population dynamics, distribution and abundance, growth
and life histories, competition, predation, herbivory,
parasitism, disease, and mutualism provide basic processes
within assemblages of living organisms that generate the
observed patterns of species diversity, abundance, and
composition at the community level.
7. Recognition of communities – two main ways
(a) environment or habitat where community occurs (e.g.
lakes, sand-dunes, coastal rock pools)
(b) largest or most abundant or prominent species (e.g.
pine forest, oak woodland, grassland, Sphagnum bog)
8. Size of community – no fixed size, can range from very small
and constrained (e.g. association of micro-organisms in
mammalian gut) to huge expanses of grassland and forest.
9. Why are similar groups of species found again and again in
similar habitats?
If the habitat provides a collection of environmental niches
and if the same niches occur in similar habitats, then they
will be filled by the same species.
Niches for particular plants, grazing animals, decomposers,
parasites, etc.
10. Community is built up of species with other dependent
species in recognisable combinations.
11. But communities found in a particular habitat type will not
be identical. Minor differences in the environment that
vary continuously in space and time may occur. Effects of
chance or history of the site may mean that some species
usually found together are missing and other more unusual
species may be present.
12. Species present in a community will vary depending on
where in the world the particular community is found.
Species growing in coastal pools on rocky shores in
Australia will be different from species growing in similar
pools in Norway. Hence the importance of biogeography
and geographical ecology in determining the available
species pool.
13. However, wherever rock pools occur, expect them to have
similar relationships between species occupying the same
collection of niches.
14. Species that assemble to form a community are determined
by (i) dispersal constraints, (ii) environmental constraints,
and (iii) internal dynamics.
Species pools:
Total Pool – function
of evolution and
history
Habitat Pool –
function of
environmental
constraints
Geographic Pool –
function of dispersal
constraints
Ecological Pool – function of internal dynamics
Community – what remains in face of biotic interactions
The Study of Communities
Within any community there is a complex series of
interactions between individuals of different
species.
The whole collection of populations may fit together
into a functional unit; the community.
Community ecology seeks to understand the way
species groupings are distributed in nature and the
ways that these groupings are influenced by their
abiotic environment (Part I of this course) and by
interactions between species populations (Part II)
How do we study communities and understand the
complexity of such systems?
1. What is the community structure?
- abiotic features noted (e.g. marine, freshwater,
marsh, desert; geology; topography; climate,
etc.)
- overall form described (e.g. terrestrial life forms
such as trees, shrubs, herbs and grasses,
mosses; aquatic mode of locomotion such as free
swimmers, planktonic drifters, bottom dwellers,
sessile adults)
2. What species are present?
3. How many species live in the community?
(Diversity) Is it species-poor or species-rich?
4. What are the abundance patterns of the species?
5. How does the community function? Trophic food
webs within the community can be investigated to
assess the importance of primary producers,
herbivores, predators, and decomposers. This
provides data on energy and nutrient cycles. See
lectures on Ecosystem Ecology (Lectures 3, 4).
6. What is the influence of the abiotic environment
on the composition and structure?
7. How does the community regenerate and sustain
itself? Population dynamics and stability (Lecture
2).
8. What is the history of the community? Long-term
ecology or palaeoecology (Lecture 5).
No community is well enough studied that
we can answer these eight questions!
Overall community structure will be determined
by features of the physical environment,
community size, longevity of the species
present, and history.
Community may be stable or unstable, have
low or high primary productivity, and may
change seasonally or even daily.
Community, ecosystem, and broad-scale
ecology are very difficult to study.
How do we study community ecology?
1. Search for patterns in the collective and
emergent properties
Collective properties – species richness and
diversity, community biomass
Emergent properties – stability, resilience,
dynamics
(e.g. for cake
- numbers or size of ingredients = collective
properties;
- taste and texture = emergent properties)
2. Patterns are repeated consistencies, such as
repeated groupings of similar growth-forms or
species in different places, or repeated trends
in richness along different environmental
gradients.
3. Recognition of patterns leads to formulation of
hypotheses about the causes of the patterns,
so-called processes.
4. Test hypotheses by making further
independent observations or by doing
experiments.
5. Much of community ecology is, by necessity,
descriptive or narrative, rather than analytical
with strict hypothesis testing or statistical
modelling.
Communities can be defined & studied and the
underlying processes identified at many scales
1. Global scale – boreal forest biome
Strong climate control
2. Boreal forest in Norway is represented by communities
dominated by Pinus (furu), Picea (gran), and Pinus and
Picea
Strong soil, topographical, and historical controls
3. At a finer scale, the field layer may differ between
different Pinus stands
Strong soil or historical (e.g. fire) controls
4. At an even finer scale, within a Pinus stand there are
animals that inhabit fallen and rotting logs, plants and
animals that live in the gut of the deer in the forest, etc.
The scale of investigation depends on the ecological
questions being asked.
The structure of oak (Quercus) woodland in
spring and summer
Chapman & Reiss
A cross-section of a typical rock pool showing the
mixed nature of the community and some of the other
organisms which inhabit the more open rocky shore.
Chapman & Reiss
The general structure of the mammalian gut and
common members of gut communities (not to scale).
Chapman & Reiss
Often difficult to study large numbers of species, so community
ecologists may work with restricted groups, e.g. plants, insects.
Some focus on guilds – group of organisms that all make their
living in a similar way (e.g. seed-eating animals in a desert, fruiteating birds in a forest, filter-feeding invertebrates in a stream).
Some guilds consist of closely related species; others may be
taxonomically unrelated.
For example, fruit-eating birds on South Pacific Islands are mainly
pigeons, whilst the same guild in USA deserts consists of mammals,
birds, and ants.
Guild concept mainly used by animal ecologists.
Life-form or growth-form or functional type used by plant
ecologists. Combination of structure and growth-dynamics (e.g.
trees, vines, annual plants, grasses, herbs (= forbs)). Like an
animal guild, plants of similar life-form exploit the environment in
similar ways.
By studying animal guilds or plant life-forms, communities can be
studied in a more manageable and coherent way than trying to
consider all species simultaneously.
All communities have attributes or features
that differ from those of the components that
make up the community and that only have
meaning with reference to the collective
assemblage or community.
These attributes are
1. Number of species
2. Relative abundance of species
3. Nature of their interactions
4. Physical structure, defined primarily by the
growth-forms of the plant components of the
community
How do we Quantify the Number &
Relative Abundance of Species in
Communities?
Species Abundances
One of the most striking features of communities
is the variation in the relative abundance of
species.
Basic questions often asked:
1. For a given community, how many species are
there and what are their relative abundances?
2. How many species are rare?
3. How many species are common?
Species abundances are usually based on
individuals per species, or variables such as
percentage cover or biomass.
Fundamental aspect of community structure –
"minimal community structure" (Sugihara, 1980)
What will be found if we go to a community and
quantify the abundance of species within a group of
taxonomically or ecologically related organisms such
as birds, shrubs, herbs, or diatoms?
Species abundance data are arranged in the form of a
species abundance distribution, that is a frequency
distribution of the number of species with X = 1, 2, 3,
… r individuals.
Insect count data from grassland based on 14 sweep
nets
X
1
2
3
4
5
6
7
9
10 11 21 28 33 120
f
32
8
9
2
3
3
3
2
1
2
1
1
1
1
X = number of individuals per species
f = frequency of species in each of the X classes
There are 389 individuals and 69 species.
Can we fit a statistical distribution model to such
species abundance data?
Hope to find a 'general' model requiring a few, easily
estimated and ecologically meaningful parameters.
Turns out that there are regularities in the relative
abundance of species in many different communities.
If you can thoroughly sample the community, there
are usually:
(1) a few very abundant species
(2) a few very rare species
(3) most species have a moderate abundance
Preston "distribution of commonness and
rarity" and the log-normal distribution (1948,
1962)
Consider abundance in relative terms and say
that one species is twice as abundant as
another.
Graph the abundance of species in samples as
frequency distribution where the species
abundance intervals are
0-1, 1-2, 2-4, 4-8, 8-16, 16-32, etc.
individuals, so-called octaves.
Frank Preston
Insect data – 389 individuals, 69 species
X
1
2
3
4
5
6
7
9
10 11 21 28 33 120
f
32
8
9
2
3
3
3
2
1
2
1
1
1
1
Octave
S(R) number of species in Rth octave (oct)
Octave 1 (0-1)
32/2 = 16
Octave 2 (1-2)
16 (from oct 1) + (8/2) = 20
Octave 3 (2-4)
4 (from oct 2) + 9 + (2/2) = 14
Octave 4 (4-8)
1 (from oct 3) + 3 + 3 + 3
Octave 5 (8-16)
2+1+2=5
+ 0 = 10
Note that abundance classes falling on the lines separating
consecutive octaves (1, 2, 3) are split between octaves
In Preston log-normal distribution, plot the
abundance classes on log2 scale (log2 of 1 = 0,
log2 of 2 = 1, log2 of 4 = 2, log2 of 8 = 3, etc.).
Each class represents a doubling of the previous
abundance class.
Plot log2 of species abundance against the number
of species in each abundance interval. Each
abundance interval is twice the preceding one.
Log-normal distribution is
S(R)  S0e
(  a2R2 )
where S(R) is the number of species in the Rth
octave from the mode
S0 is an estimate of the number of species in the
modal octave (the octave with the most species)
a is an inverse measure of the width of the
distribution
(a = ½ where  is the standard deviation)
e is exponential function or antilog
Estimation of parameters S0 and a
a  log n
S(o) S(R
max
)
2
Rmax
where S(o) is the observed number of species in the
modal octave and S(Rmax) is the observed number of
species in the octave most distant from the modal
(indicated by Rmax)
Parameter a has been found to be about 0.2 for a
large number of samples in ecology. It has been
shown that this ‘rule’ may be a product of the
mathematical properties of the log-normal
distribution. As the total number of species in the
community varies from 20 to 10000, a will vary from
0.3 to 0.13 (assuming that the underlying distribution
follows the so-called ‘canonical log-normal’
distribution).
An estimate of S0 is obtained either by fixing it
at the observed value for the number of species
in the modal octave, S(o), or by estimating it

S0  e logn S (R )  a2R 2

where logn S (R) is the mean of the
logarithm of the observed number of species
per octave, a is estimated as above, and R2
is the mean of all the R2s.
Insect data
Octave
1
2
No of individuals
per species
0-1
1-2
Observed
S(R)
16
20
Expected
S(R)
14.5
15.9
3
4
5
6
2-4
4-8
8-16
16-32
14
10
5
2
15.5
11.0
6.9
3.6
7
8
32-64
64-128
1
1
1.6
1.1
2 = 2.76; degrees of freedom = octave classes – 2 = 6
Suggests good fit to theoretical log-normal model by
observed data.
If communities really follow log-normal
distribution, can predict how many species might
have been unobserved in the community (S*)
S* = 1.77(S0/a)
where S0 = number of species in modal octave
and a is a measure of the curve's width.
In this case S* = 23
In a sample of 389 individuals and 69 species,
likely that there are 23 species missed.
Problems of sampling natural assemblages.
Distributions
of desert
plants and
forest birds
Desert plants - few species have cover > 8% or <
0.15%. Most are intermediate
- "bell-shaped" or "normal"
- log scale of cover, so "log-normal"
Ohio birds
- "log-normal"
But not all data show full normal plot.
Depends on sample size – easy to catch
common species, more effort needed to
catch rare species.
Sample size
and lognormal
distribution
How to explain the log-normal distribution of
commonness and rarity?
May (1975) proposed that the log-normal
distribution is the product of many random
environmental variables acting upon the
populations of many species. Relative abundances
of large, heterogeneous assemblages of species
governed by many independent factors will,
according to the central limit theorem of statistics,
be log-normally distributed.
True for any large heterogeneous collection, e.g.
distribution of wealth in the USA and the
distribution of the human population among the
nations of the world.
Is the log-normal distribution just a mathematical
artefact or does it reflect important biological
processes?
May be a consequence of species within a
community subdividing available niche space and of
equilibrium or balance within community.
Very robust, may be the result of the law of
large numbers or may be the result of biological
processes.
Emphasises that few species are very abundant
or extremely rare. Most species are
moderately abundant.
Remarkably consistent and best described (though
least understood!) pattern in community ecology.
Apparent ‘rules’ in species-abundance models
1. a of the log-normal distribution ≈ 0.2
2. Canonical hypothesis of Preston (1962)
Preston examined many community data-sets
with the log-normal model to examine the
relationship between species per octave and the
total number of individuals in species per octave.
RN
S(R) Number of
species per octave
Log-normal curve
I(R) Individuals per octave
-7
0
+7
Rmax
Associated individuals
curve
Octaves
I(R) = S(R)N(R) where N(R) is the number of
individuals per species in the Rth octave
Preston compared these two curves in terms of
the relationship between Rmax (the octave for the
most abundant species of species curve) and RN,
the octave of the mode of the individuals curve
q = RN/Rmax
If q = 1, the log-normal species curve is
canonical
Empirical rule that tends to apply to many
community data
Why should a be about 0.2 and q about 1?
May (1975) showed that the two ‘rules’ may be
properties of the log-normal distribution.
1. General relationship between the total
number of species and individuals, S and N, and
parameters a and q
2. For values of S from 20-10000 and for N
from 10S to 107S, parameter a lies in range
0.1-0.4 and q is 0.5-1.8
Are a and q therefore just statistical
generalities associated with large
samples?
Lord Bob May of Oxford
Sugihara has shown that the canonical hypothesis (q =
1) is obeyed too strictly by ecological communities to be
totally explained by May’s ‘properties arguments’.
Turns out to be a unique relation between S and 
(standard deviation of the log-normal distribution) for a
given value of q.
Natural communities closely approximate the canonical
form (q = 1), whilst disturbed (e.g. pollution, fire)
communities did not fit the canonical form.
Canonical form with q = 1 may indicate that the
community is stable or, at least, in a high degree of
equilibrium (or at least dynamic equilibrium – see
Lecture 2).
Use species abundances, log-normal models, and
canonical form as a pattern detection tool, regardless
of whether the underlying hypotheses proposed for the
model are correct or not.
Rank-Abundance Diagrams
Show distribution of all species abundances in a
community for all m species present. Plot abundance
pi for all i = 1,…,m species where pi is proportional
abundance
Plot pi for the most abundant species first, then the
next most common, and so on against species rank
Can be drawn for different
communities or same
community at different times
Grassland fertilised
1856-1949
Try to fit mathematical equations or ecological models
to rank-abundance diagrams
DD - dominance decay
MF - MacArthur
fraction
RF - random fraction
RA - random
assortment
CM - composite
DP - dominance preemption
Statistical models: log-series (LS)
log-normal (LN)
Niche models:
broken-stick (BS)
geometric series (GS)
For some explanation of these models, see Begon et al.
(2006 pp. 472-473).
Species Numbers (= Richness) and
Species Diversity
Species diversity consists of two components
1. Number of species in community – 'species richness'
2. Species evenness or equitability – how the species
abundances (e.g. cover, frequency) are distributed
among the species.
Two communities
1 - 10 species: 90% of individuals belong to species A;
10% of individuals belong to species B, C, D, E, F, G,
H, I, J
2 - 10 species: 10% of individuals belong to each of
species A-J
Community 1 has low evenness,
2 has maximum evenness
Richness indices
Evenness indices
Richness index + evenness index = Diversity
index
Confound several properties of community
structure, namely number of species; relative
species abundance (evenness); and
homogeneity and size of the area sampled.
Species identity not considered.
Richness indices
S – total number of species found in a community
But S depends on sample size and the time spent
searching
Need to estimate S independent of sample size
But samples usually of different size
Rarefaction analysis – estimates how many species
would be found in a sample of n individuals [denoted
as E(Sn)] drawn from a population of N total
individuals among S species.
  N  ni  N  

E(Sn )   1  

i 1 
 n  
  n
s
where ni = number of individuals of species i
Rarefaction curves for
three bird habitats
showing expected
numbers of species
(E(Sn)) as a function
of sample size
Three habitats
20
9
38 species (S), 122 birds (N)
14 species (S), 50 birds (N)
36
8 species (S), 62 birds (N)
How many species would be observed if all habitats
had same sample size of 50 birds each?
E(Sn) habitat
20
9
36
26.9 species
14.1 species
7.8 species
Estimate of the total number of species S*
(from the log-normal model) can also be
used as a richness index.
Requires a statistical fit of the species
abundances to the log-normal frequency
distribution.
Computationally difficult, but not much more
difficult than estimating E(Sn) in rarefaction
analysis.
Evenness or ‘equitability’ indices
Evenness can be quantified by expressing Simpson’s
index
1 
1s
l
 pi
l 1
2
(see below)
as a proportion of the maximum value l possible
when we assume that all individuals are completely
evenly distributed amongst the species
Lowest value is 1: higher the value, greater the
evenness. The maximum value is the total number
of species; lmax = S. See below for more about
evenness indices.
1/ l
1
1

Thus, evenness E = l  s
S
2
max
 pi
l 1
Diversity indices
Combines species richness and
evenness of relative abundance and
compares richness and evenness of
relative abundances between two or
more samples
Two forests, 5 species only but (b) has higher evenness
5 species; 84% A, 4% B,
4% C, 4% D, 4% E
5 species; A, B, C, D, &
E each 20%
Forest (b) more diverse
Two common diversity indices that combine
richness and evenness
1. Simpson (1949) index
s
l   pi
2
i 1
where pi is the proportional abundance of species i
= ni/N
where ni is the number of individuals of species i
and N is the total number of individuals in sample.
Emphasises the evenness of the most abundant
species (known with least error).
Ranges from 0 to 1.
As the greater the value of l, the lower the diversity
is, conventional to use
1 – l as Simpson's index of diversity, D
Ranges between 0 and 1. In the absence of any
diversity (only one species is present), the value of l
= 1 and D = 0.
D represents the probability that two individuals
randomly selected from a sample will belong to
different species.
Often used as 1/l. Lowest value is 1; higher the
value, greater the diversity. The maximum value in
this case is the number of species in the community
(species richness).
Important to know if using l, 1 – l, or 1/l.
2. Shannon-Wiener index (H') (also known as
Shannon-Weaver index)
Based on information theory and is a measure
of the average degree of uncertainty in
predicting what species an individual chosen at
random from a collection of S species and N
individuals will belong.
Average uncertainty increases as species
number increases and as the distribution of
individuals among the species becomes even.
Thus;
(1) H' = 0 if and only if there is one species
present
(2) H' is maximum only when all S species are
evenly distributed
s
H '   pi log e pi
i 1
where pi is the proportion of species i
loge is natural logarithm of pi
S is number of species
Simply determine proportions of each species,
pi, and the loge of pi. Multiply each pi times loge
pi, and sum the results for all species from 1 to
S. As the sum will be negative, H' is the
opposite sign.
Evenness
s
H'
J

Hmax
  pi loge pi
i 1
loge S
where H’ is Shannon-Wiener diversity index,
S is number of species, and Hmax = logeS
Two forests, 5 species only but (b) has higher evenness
5 species: 84% A, 4% B,
5 species: A, B, C, D, & E
4% C, 4% D, 4% E
each 20%
H' = 1.610
H' = 0.662
Forest (b) more diverse
Hill's (1973) family of diversity indices
s
N A  (pi )1/(1 A)
i 1
N0 = S
S is total number of species
N1 = eH'
H' is Shannon's index
N2 = 1/l
l is Simpson's index
Units are number of species, not information bits
N0
same weight on all species
N1
more weight on abundant species
N2
most weight on very abundant species
Most useful as the units are number of species
N0 = number of all species present regardless of
their abundances
N1 = number of abundant species
N2 = number of very abundant species
N0 > N1 > N2
‘Effective number of species’ – measure of the
degree to which proportional abundances are
distributed among species. Measure of number of
species where each species is weighted by its
abundance.
N0, N1, and N2 differ only in their tendency to
include or ignore rare species
11 species
abundances are 90, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1
N2 = 1.23
N1 = 1.74
N0 = 11
Evenness indices revisited
If all species are equally abundant, obvious that
evenness index should be maximum and decrease
towards zero as the relative abundances of the
species diverge away from evenness
V 
D
Dmax
or
D  Dmin
V 
Dmax  Dmin
where D is some observed diversity index and Dmin
and Dmax are the minimum and maximum values,
respectively, that D can obtain
Some useful evenness measures, all here in
terms of Hill’s diversity numbers N0, N1, and N2
1.
H
log n (N1)
E1 

log n (S) log n (N0)
= J of Shannon-Wiener evenness index
H’ is Shannon-Wiener diversity index
2.
e H
N1
E2 

S
N0
H’ is Shannon-Wiener diversity index
3.
4.
5.
e H  1 N1  1
E3 

S 1
N0  1
E4 
1 l N2

H
e
N1
1 l  1 N2  1
E 5  H

e 1
N1  1
Hill ratio
Modified Hill ratio
This approaches zero as a single species
becomes more and more dominant, unlike
E4 which approaches 1
E5 is preferred evenness index
Evenness index should be independent of
number of species in the sample
E1 (= J) strongly affected by species richness
E2 and E3 also strongly sensitive to richness
E4 and E5 unaffected by richness. Best to use.
Species
Abundances
E1
E2
E3
E4
E5
3
500, 300, 200
0.94
0.93
0.90
0.94
0.91
4
500, 299, 200, 1
0.75
0.71
0.61
0.94
0.90
E4 and E5 remain relatively constant with sampling
variations and hence tend to be independent of
sample size. Computed as ratios and S, the number
of species, is both the numerator and denominator.
Cancels impact of number of species in the sample.
In reality, E4 and E5 are the ratios of the number of
very abundant species (N2) to the number of
abundant species (N1).
Relative evenness can also be compared by
examining the steepness of rarefaction curves.
Higher evenness is equated
with a steeper rarefaction
curve. Habitat 20 has
highest evenness, habitat
36 has the lowest.
Uses in ecology
Changes in
diversity (H’) and
equitability (J) in
a control plot and
fertilized plot
1850-1950
Decline in diversity and equitability with time in the
fertilized plot. Possibly due to higher growth rates of
taller species allowing them to dominate and exclude
other smaller species.
Not all Species are Equal!
In a functional role, not all species in a community
appear to be equal.
1. Few common species with a high population
density or relative abundance. Called dominants.
Dominance is the converse of diversity. Simpson's
l is often used as a measure of dominance. A
value of 1 would represent total dominance (only
one species present).
Dominance may not be numerical abundance but
may be biomass, functional importance, or size of
the individuals.
2. Many rare species with a low population density
or relative abundance. Called rarities.
3. Keystone species – may be less abundant
but play a crucial role in the function of the
community.
Keystone species have a unique and significant
role through their activities and their overall
effect on the community may not be related or
proportional to their abundance.
If removed, major changes in community
structure occur along with a significant loss of
diversity.
Role of keystone species may be to create or
modify habitats or to influence the interactions
between other species.
Examples of keystone species are
1. Herbivores e.g. African elephant in savanna
communities
2. Predators e.g. sea otters (Enhydra lutris) eat
sea-urchins in kelp sea-weed beds. Kelp beds
provide habitats for many other species. If
sea otters decline, sea-urchin populations
increase resulting in overgrazing of kelp beds
and loss of habitat for many species.
3. Coral Oculine arbuscula – more than 300
invertebrate species live among its branches.
Keystone species are like pieces in a Jenga game
In a game of Jenga,
players successively take
away parts and place them
on top until the structure
becomes unstable and
crashes. Each part can
thus be a keystone. When
parts are replaced at other
positions, the stability of
the Jenga structure can be
maintained.
Keystone species may be like pieces in a Jenga game.
But we do not really know. Very difficult to find out.
Rank-Abundance Curves Revisited
Plot the relative abundance of species against their
rank in abundance. Provides useful graphical
summary of evenness and richness. No need to try
to match to particular
theoretical model.
Just a useful diagram.
Forest – community b
has all five species
equally abundant
Rank-abundance curves for two forests
Reef fish – greater
evenness in Central Gulf
Rank-abundance curves for
reef fish communities
Caddis flies – greater
richness and evenness
in mountain stream
Rank-abundance curves for
caddis flies
What Determines Diversity?
High biodiversity is often associated with high
eco-complexity or environmental complexity.
In general species diversity increases with
environmental complexity or heterogeneity.
But one aspect of the environment may be
important to one group of organisms but may
not be important to another group.
Need to know something about the ecological
requirements of species (niches) to predict
how environment influences their diversity.
Environmental Complexity
1. Forest complexity and bird species diversity
Competition influences species realised
niches.
Competitive exclusion principle predicts that
co-existing species will have different realised
niches.
Warblers (sangere) in eastern USA forests
Community structure: vertical stratification
100
30
20
50
10
ft
m
Tropical
rain forest
Coniferous
forest
Deciduous
forest
Thorn
forest
Thorn
scrub
Tall-grass
prairie
Short-grass
prairie
Desert
scrub
Emergent
Forest community
structure
Birds,
invertebrates,
bats
Canopy
Birds,
reptiles,
amphibians,
lichens, mosses
Understorey
Shade-tolerant
plants, birds,
squirrels,
lizards,
chipmunks
Snag
Floor
Rotting debris,
worms,
insects,
bacteria
Subsoil
Bole
Nematodes,
micro-organisms
Five different warblers (sangere)
Essential to study community structure to provide basis for explaining
co-existence of different species of same genus in forests
Species forage in different layers in forest.
Distributions may be influenced by vertical
structure of vegetation.
Mount Desert Island, Maine
Robert McArthur measured relationship
between volume of vegetation above 6 m
and warbler abundance
Warbler diversity
increased as
stature of
vegetation
increased
i.e. species
diversity
increased with
habitat size.
What about
habitat diversity?
Estimated forest
habitat diversity
by ShannonWiener index.
Stature of vegetation and no. of
warbler species
Foliage height and bird species diversity
In absence of black-throated green warbler, the
yellow-rumped warbler expands its range
Structure PLUS between-species interactions
are important
General (but not universal!) pattern that species
diversity (biodiversity) increases with
environmental complexity (eco-complexity) or
habitat diversity.
mammals
reef fish
lizards
birds
reptiles
marine gastropods
What about plants?
2. Niches of algae and terrestrial plants
At least 270,000 species of terrestrial plants
Provides great scope for animal niche
specialisation
But how can we explain the diversity of primary
producers?
"The paradox of the plankton" G.E. Hutchinson (1961)
Paradox because plankton live in relatively simple
environments (open water of lakes and oceans) and
compete for N, P, Si, etc. and yet many species coexist without competitive exclusion.
Same for terrestrial plants – how can they co-exist?
Need to understand the nature of their niches.
Algal niches – defined by nutrient requirements
David Tilman - competition experiments with
fresh-water diatoms Asterionella
formosa and Cyclotella
meneghiniana in relation to Si/P
ratio
Ratio of silicate to phosphate
High Si/P ratios, Asterionella dominant in P
limited situations. Takes up P faster, depletes
environment of P, eliminates Cyclotella.
Low Si/P ratios, Cyclotella dominant as Si limits
growth of Asterionella and so Asterionella cannot
deplete the P and eliminate Cyclotella.
When both Si and P are limiting (medium ratios)
two species can co-exist.
Two planktonic species can co-exist in a lake
because of spatial variation in P and Si values.
Niches of plants and algae largely defined on
basis of nutrient requirements (e.g. N, P, K,
Si) and responses to physical or chemical
conditions (e.g. temperature, soil pH,
moisture).
Thus environmental variation in availability
of nutrients, temperature, moisture, pH, etc.
creates the environmental complexity
required for plant species co-existence.
Aquatic environment
Spatial variations in
NO3 and SiO2 (also
phosphate and
chlorophyll a) create a
wide range of environmental complexity
Concentrations of nitrate and
silicate in Pyramid Lake, Nevada
Terrestrial environment
0.5 ha plot (69 m x 69 m)
301 sampling points
Measured soil moisture and soil NO3 in an abandoned
agricultural field in Michigan.
10-fold
difference
across study
plot
No correlation
between the
two variables
Shows considerable spatial variability within a small
area.
How does this spatial heterogeneity in essential
resources influence plant distribution and diversity?
Amazon forest – one of the most complex vegetation
types known.
Jordan (1985) showed
(1) large numbers of species live within most
tropical plant communities, and
(2) there are a large number of plant communities
in a given area.
There is thus a high alpha-diversity (diversity within
habitat or community) and high beta-diversity
(between habitat or community diversity).
There is also high gamma-diversity (rich 'speciespool') due to historical reasons.
Small differences in soil properties result in
different plant communities. Six types in 2500m
over an elevational range of less than 8 m.
Granite bedrock, clay subsoil, varying amounts of
sand, small variations in topography determining
depth of the soil above the groundwater.
Communities - Hill tops, shallow sand
- Thicker sand
- Stream edges &
floodplain
- Above flooding level
- 1.2 m above stream
level
'Mixed'
'Yévaro'
'Igapó'
'Caatinga'
'Campina'
- >2 m above stream
'Bana'
level
All in 2500 m and 8 m elevational range
Subtle changes in physical and chemical environment
gives high eco-complexity and hence high
biodiversity
3. Role of increased nutrient availability and
enrichment
Generally there is a negative relationship between
diversity and nutrient availability.
As nutrients increase, species diversity decreases.
Soil fertility and
plant species in
Ghana forests
Park Grass Experiment, England since 1856
Shows decline in diversity on plots that have been
fertilized by N, P, and K from 49 species to 3 species
Control plots – no change.
Fertilization and
plant diversity
Why should increased nutrients (N, P, K)
reduce diversity?
Reduces the number of limiting nutrients.
When all limiting nutrients are abundant, light
and space remain as the limiting resources for
plants.
Only those species most effective at
competing for space and light above-ground
will survive and so diversity decreases.
What about below-ground changes?
Ectomycorrhizal fungal diversity along a soil
nitrogen gradient downwind from a fertilizer
plant on Kenai Peninsula, Alaska
Gradient from 13.3 mg kg-1 to 243 mg kg-1
extractable NO3
Looked at ectomycorrhiza on roots of Picea
glauca (white spruce) trees.
Clear decline in
mycorrhizal diversity
with increase in soil
nitrogen.
Relationship between soil
nitrogen and ectomycorrhizal
community diversity
Possibly a change from
species specialised for
nitrogen uptake under
conditions of low
available N to small
number of fungi
associated with
unusually high soil
fertility.
Environmental diversity (eco-complexity)
can certainly account for much of the
observed patterns in diversity.
What about the role of disturbance on
diversity?
Disturbance and Diversity
Ecologists tend to assume environmental conditions
remain more or less stable. Equilibrium
Lotka-Volterra competition models and predatorprey models assume a constant physical
environment.
But the physical environment varies continuously in
space and time at all scales. As a result, the biotic
environment will also vary, as will the frequency and
intensity of disturbance. Non-equilibrium
Disturbances often occur when there is a rapid shift
from 'average' conditions (e.g. storms).
"Discrete, punctuated killing, displacement, or
damaging of one or more individuals (or colonies) that
directly or indirectly creates an opportunity for new
individuals (or colonies) to become established"
(Sousa, 1984)
"Any relatively discrete event in time that disrupts
ecosystem, community, or population structure and
changes resources, substrate availability, or the
physical environment"
Scale-dependent process – spatial and temporal scales
Many types of disturbance
- abiotic: fire, hurricanes, ice storms, flash floods
- biotic: disease, predation, grazing
- human: forest clearance
Joseph Connell
'intermediate
disturbance hypothesis'
As all communities experience disturbance and
as environment is never stable, proposed that
diversity is a result of changing conditions and
not competitive accommodation at equilibrium.
Predicts that intermediate levels of disturbance
promote higher levels of diversity.
Intermediate disturbance hypothesis
Intense and/or frequent disturbance – only a few
species able to colonise and complete their life
cycles between the frequent disturbances.
Mild and/or infrequent disturbance – only a few
species are strong competitors at using available
resources or most effective at interference
competition.
At intermediate levels of disturbance, there is
sufficient time between disturbances for many
species to colonise but not long enough for
competitive exclusion.
1. Intertidal zone (Sousa 1979)
Algae and invertebrates growing on boulders.
Small boulders more likely to be disturbed by
waves and storms than large boulders.
Estimated wave force needed to move boulders
3 types - frequent movement (42% per month)
intermediate movement (9% per month)
infrequent movement (1% per month)
Number of species recorded
Levels of disturbance and diversity on intertidal boulders
2 species on low-disturbance boulders
4 species on intermediate-disturbance boulders
1 species on high-disturbance boulders
2. Temperate grasslands
Main disturbance in natural prairie grasslands is
trampling by large animals and burrowing by small
animals.
Prairie dogs (Cynomys spp.)
•plant-eating rodents
•1 kg as adult
•live in colonies
•10-55 individuals per hectare
•build extensive burrows: 1-3 m
deep, 15 m long, diameter 13-15 cm
•excavate 200-225 kg of soil
•create mounds 1-2 m diameter
Major disturbance factor on prairie
grasslands. Creates vegetation patterns.
Patchiness of
vegetation
Plant species diversity
Too much disturbance – only a few colonisers
can grow
Too little disturbance – only the major
competitors can grow
However, prairie dogs are thought of as an
agricultural pest and populations have fallen
by 98% in last century.
Pocket gophers have similar ecological role as
prairie dogs and maintain species diversity in
prairie grasslands.
3. Human disturbance
Tend to think of Panamanian rain forests as
undisturbed ecosystems and yet they have high
diversity. How is this possible? Are they
disturbed?
Palaeoecology – examine pollen and spores
preserved in lake sediments covering the last
3000-5000 years (Lecture 5).
Lake Wodehouse, Panama
Pollen and charcoal
1. Charcoal and Zea (corn) appear 3900 years ago
2. Prior to that time, was a swamp with mature
tropical forest
3. Charcoal and Zea disappear 310 years ago
4. Forest species increase in abundance
Appears here and elsewhere in tropics, that lowintensity human disturbance involving slash-andburn cultivation has been occurring for last 500011000 years.
Low-intensity human disturbance may be an integral
part of rain forest system (and many other systems).
Contrasts with massive clear-cutting of Amazonian
rain forest today. Results in much reduced diversity.
4. European calcareous grasslands
Very species-rich communities – 50 species m-2
High diversity is maintained by moderate levels of
human disturbance.
Grasslands created by humans and forest
clearance. Used for livestock grazing and
harvesting hay for winter fodder.
Grazing and mowing resulted in high plant
diversity.
When traditional land-use was abandoned,
diversity decreased and monoculture of the grass
Brachypodium pinnatum developed.
Species-rich
grassland,
Pewsey
Brachypodium
pinnatum turf,
Barnock Hills
Changes in plant species coverage
Bobbink & Willems (1991) working in Limburg, SE
Holland, investigated if they could reverse the
declines in diversity by using traditional autumn
mowing.
Tried autumn and summer mowing 1982 – 1986.
Brachypodium
pinnatum
Richness
Summer
77  34%
15.6  21.2
Autumn
75  80%
7.2  7.8
Why the difference between summer and traditional
autumn mowing?
Investigated
(1) autumn mowing
(2) late summer mowing
(3) early summer mowing
(4) early summer + autumn mowing
Only mowings (2) and (4) diminish the Brachypodium
pinnatum by reducing carbohydrates in the rhizomes
that are important for shoot formation. By reducing
the carbohydrates and shoot formation, reduce the
competitive ability of Brachypodium.
But why is the traditional autumn mowing no longer
sufficient to maintain the original high diversity of this
grassland?
Recent human activity has altered the nitrogen
cycle, increased the atmospheric N content, and
increased the soil N.
Increased soil N appears to strongly favour
Brachypodium.
Another example of increasing nutrient
availability reducing plant diversity by favouring
those species that are the most effective
competitors for the remaining resources.
Shows complex relationships within
communities and the determinants of diversity.
What Determines Community
Structure?
Most fundamental process in nature is
acquiring food or energy and nutrients needed
for assimilation.
Species interactions of predation, parasitism,
competition, and mutualism all important in
obtaining resources.
Food chain
Grass
Insect
Bird
Bird of prey
Food chains
never this
simple.
Numerous
chains fused or
meshed into a
complex foodweb with
complex links
leading from
primary
producers to
consumers.
Hypothetical food-web
P – top predator, not eaten
by other species in foodweb
C1, C2, - intermediate
species, C1 is an omnivore,
C2 is a carnivore
H1, H2, H3 – intermediate
species, herbivores
A1 and A2 – basal species,
primary producers
Real-life food-web for Tuesday Lake, Michigan, USA
de Ruiter et al. (2005)
How do species co-evolve and shape complex webs of
mutualistic interactions? Part of community structure
Plants and free-living pollinators and seed-dispersal
agents. Most visible, diverse, and mutualistic
interactions. Involves dozens or even hundreds of plant
and animal species.
Do these mutualistic interactions lead to a predictive
pattern of links between species?
Using network theory, can
show that specialisation
(bees only visiting flowers
of 1 or 2 species) within
the web is nested. In a nested web, there is a core
group of generalists that interact with each other and
extreme specialists that interact only with generalist
species.
Result is a web with many asymmetries in degree of
specialisation among interacting species. In
contrast, interactions between predators and prey
or herbivores and plants are often in compartments
and form small clusters within the broader
interaction web.
Studies in montane forest in SE Spain, Bascompte
et al. (2006 Science 312: 431) show that the
distribution of specialists and generalists within
these webs is unlikely to be due to chance.
Asymmetries in specialisation between pairs of
interacting species are the rule.
Plant might rely heavily on seed-dispersal by a
particular seed-eating (frugivore) species, but the
same frugivore might consume fruits from many
plant species.
Assymmetry in
specialisation
promotes species
coexistence within
these interactions
over evolutionary
time.
Complex mutualistic webs are not haphazard
collections of specialists and generalists
Evolution and co-evolution appear to shape these
interactions in a predictable way regardless of
the exact species composition
An important part of community structure is the
role of mutualistic interactions
Perhaps there will, one day, be a theory of coevolution and community structure
We are a long way from any such theory!
Different Concepts of the
Community
Community – group of species that occupy a given
area interacting directly or indirectly.
How important are these interactions?
Major debate in ecology since the early part of the
20th century.
Two contrasting concepts
1. Organismal concept of community
– Frederic E. Clements
2. Individualistic concept of
community – Henry A. Gleason
1. Organismal concept of community – each
species represents an interacting, integrated
component of the whole.
Species have similar distributions along an
environmental gradient. May peak at same point.
Transition between associations (communities) are
narrow.
Suggests a common history and similar
fundamental niches (responses and tolerances).
Mutualism and co-evolution are important in the
evolution of species in the community.
Community is thus an integrated whole; the species
interactions are the "glue" that holds it all together.
Discrete units, plant associations, alliances, etc.
Plant ecology, classification, phytosociology.
2. Individualistic concept of community –
relationships between co-existing species are
a result of similarities in their requirements at
that one point in space and are not a result of
strong interactions or common history.
Gleason proposed that species abundances change
so gradually along gradients that it is not practical
to divide the vegetation into associations. Species
distributions do not form clusters but represent
independent or individualistic responses of species.
Transitions are gradual and difficult (or
impossible!) to identify.
Community here is merely the group of species
found to co-exist under a particular set of
environmental conditions.
Species distributed as a continuum in response to
variation in the environment in space and time.
Gradient analysis and ordination.
Models of taxa along gradients
Community
concept
Individualistic
concept
Kent &
Coker
(1992)
Community - unit theory
R.H. Whittaker (1956) Ecological Monographs 26: 1-80
Kent & Coker (1992)
Topographic distribution of vegetation types on an idealised
west-facing mountain and valley in the Great Smokey
Mountains, USA.
Community - unit - vegetation of an area is distributed as a
mosaic, so-called climax pattern.
Broadly similar environmental factors (both abiotic and biotic)
occur and repeat themselves in an area. Not all areas
can be placed in one or other type. Boundaries may be
distinct or vague (ecotones).
60 - 80% can be unambiguously assigned to particular
vegetation types.
20 - 40% can not be assigned because they are transitional or
ecotonal areas between types.
Community - unit  vegetation - landform unit. Features of
landscape.
Noda - reference points in a continuum of either geographical
or environmental space.
Continuum of species responses in environmental space or
gradients. Features of underlying environment.
Major differences between these two concepts
are the relative importance of interactions,
evolutionary history, and co-evolution in
determining community structure.
Evidence for both concepts – the natural world
shows both discontinuous (organismal concept) and
continuous (individualistic concept) change at
different spatial and temporal scales).
Testing of these competing concepts and
hypotheses requires knowledge about community
history and development through time. Lecture 2
on Community Ecology and Dynamics.
Gradients and landscapes
Austin &
Smith (1989)
Patterns of co-occurrence of four species on a landscape along an
indirect environmental gradient altitude; note continuous variation
of composition along altitude gradient. A plant community is a
landscape concept and recognition of communities depends on the
frequency of environmental combinations in a particular landscape.
Important distinction between geographical distribution and
environmental distribution.
In geographical space, have species associations A, AB, B, C,
and D with BC and CD as 'ecotones'. These associations are a
consequence of the spatial pattern of the landscape.
In environmental space, find a continuum of species A, B, C,
and D replacing each other with increasing altitude.
Communities or associations are a function of the
landscape examined.
Continuum concept applies to the environmental space,
and not necessarily to geographical distance on the ground or
to any indirect or complex environmental gradient.
Community concept and continuum concept not alternatives
but are features of vegetation viewed in different ways geographical space or environmental space.
How to Analyse Community-Scale
Data?
Classification and gradient analysis (= ordination)
Simple example - European food
(from A Survey of
Europe Today, The
Reader’s Digest
Association Ltd.) %
of all households
with various foods in
house at time of
questionnaire. Foods
by countries.
GC ground coffee
IC instant coffee
TB tea or tea bags
SS sugarless sugar
BP packaged biscuits
SP soup (packages)
ST soup (tinned)
IP instant potatoes
FF frozen fish
VF frozen vegetables
AF fresh apples
OF fresh oranges
FT tinned fruit
JS jam (shop)
CG garlic clove
BR butter
ME margarine
OO olive, corn oil
YT yoghurt
CD crispbread
90
49
88
19
57
51
19
21
27
21
81
75
44
71
22
91
85
74
30
26
D
82
10
60
2
55
41
3
2
4
2
67
71
9
46
80
66
24
94
5
18
I
88
42
63
4
76
53
11
23
11
5
87
84
40
45
88
94
47
36
57
3
F
96
62
98
32
62
67
43
7
14
14
83
89
61
81
16
31
97
13
53
15
NL
94
38
48
11
74
37
25
9
13
12
76
76
42
57
29
84
80
83
20
5
B
97
61
86
28
79
73
12
7
26
23
85
94
83
20
91
94
94
84
31
24
L
27
86
99
22
91
55
76
17
20
24
76
68
89
91
11
95
94
57
11
28
GB
72
26
77
2
22
34
1
5
20
3
22
51
8
16
89
65
78
92
6
9
P
55
31
61
15
29
33
1
5
15
11
49
42
14
41
51
51
72
28
13
11
A
73
72
85
25
31
69
10
17
19
15
79
70
46
61
64
82
48
61
48
30
CH
97
13
93
31
43
43
39
54
45
56
78
53
75
9
68
32
48
2
93
S
96
17
92
35
66
32
32
11
51
42
81
72
50
64
11
92
91
30
11
34
DK
96
17
83
13
62
51
4
17
30
15
61
72
34
51
11
63
94
28
2
62
N
98
12
84
20
64
27
10
8
18
12
50
57
22
37
15
96
94
17
64
SF
70
40
40
62
43
2
14
23
7
59
77
30
38
86
44
51
91
16
13
E
13
52
99
11
80
75
18
2
5
3
57
52
46
89
5
97
25
31
3
9
IRL
Classification
Key –
SF Finland
N Norway
DK Denmark
S Sweden
GB Great Britain
IRL Ireland
D West Germany
B Belgium
L Luxembourg
F France
CH Switzerland
NL Holland
P Portugal
A Austria
E Spain
I Italy
Dendrogram showing the results of minimum variance
agglomerative cluster analysis of the 16 European countries
for the 20 food variables listed in the table.
Ordination
Key:
A Austria
B Belgium
CH Switzerland
D West Germany
DK Denmark
E Spain
F France
GB Great Britain
I Italy
IRL Ireland
L Luxembourg
N Norway
NL Holland
P Portugal
S Sweden
SF Finland
Correspondence analysis of percentages of households in 16
European countries having each of 20 types of food.
Classification and/or Ordination
Traditionally classification associated with the discontinuum or
community concept of vegetation and ordination with the
continuum concept.
Reflects the history of the methods but is the distinction
valid?
Approaches are complementary: choice depends on the aim
of the study.
Vegetation mapping - classification is necessary.
Fine-scale studies -
ordinations are necessary to find
repeatable patterns and discontinuities
in composition.
Not a case of Classification or Ordination, but Classification
and/or Ordination.
Diversity Components at Community Scale
R.H. Whittaker suggested several concepts of diversity:
: diversity on a sample plot, or 'point' diversity (or within-habitat
diversity). Community
: diversity along ecological gradients (or between-habitat diversity).
Differentiation diversity. Many meanings - poorly understood.
Cannot be estimated unless there are known environmental
gradients or the underlying latent structure of the data has been
recovered. Between-community
: diversity among parallel gradients or classes of environmental
variables. Product of -diversity of communities and differentiation among them. Landscape
: diversity between landscapes. Differentiation diversity between
landscapes. Between-landscape
ε: the total regional diversity of an area: sum of all previous
components. Applicable to broad biogeographical areas. 'Species
pool'. Regional
In practice,  and  diversities are rarely distinguished. ε is often used
to designate the total diversity of a landscape, geographical area,
or island. Incorrectly called  diversity.
Ecologists recognise many types of diversity
•community (-diversity)
•between community (-diversity)
•landscape (-diversity)
•between landscapes (-diversity)
•regions (e-diversity)
Odgaard 2007
Conclusions and Summary
1. Community is a collection of plants and animal
populations found in one habitat type in one
area and integrated to a degree by competition,
complementarity, and dependence.
2. Species occur together because of the niches
available in that habitat type.
3. Communities are most commonly recognised
by their habitat type or the largest or most
abundant species.
4. Communities are very complex and many
questions arise:
- What is the community structure?
- What species are present?
- How many species are present?
- What are the abundance patterns of the species?
- How does the community function?
- What is the influence of the abiotic environment
on the community?
- How does the community regenerate and sustain
itself?
- What is its history?
5. Animal ecologists focus on guilds – organisms
that function together. Plant ecologists may
focus on life-forms or functional types.
6. Species abundance patterns usually follow the
log-normal distribution, with few very abundant
or very rare species, and many medium
abundance species.
7. Log-normal distribution may just be a
mathematical artefact and a result of the law of
large numbers or it may be a result of biological
processes.
8. Species diversity consists of species richness
and species evenness.
9. Species richness depends on sample size and
can be standardised by rarefaction analysis.
10. Two common diversity indices are the Simpson
index and the Shannon-Wiener index. Simpson
considers the evenness of the very abundant
species, Shannon-Wiener considers the
abundant species. Hill’s diversity numbers are
very useful summaries and combine richness
and evenness.
11. Rank-abundance curves display evenness and
diversity graphically.
12. Species diversity is higher in complex
heterogeneous environments.
13. High nutrient levels correlate with reduced
diversity of algae, plants, and fungi.
14. Intermediate levels of disturbance promote
higher diversity.
15. Human activity is an ancient feature of the biosphere and has provided intermediate disturbances
for long periods of time.
16. Recent intensive human activity (widespread forest
destruction, atmospheric N pollution) is decreasing
community diversity.
17. Food acquisition, food chains, and food-webs are
potential factors in determining community
structure.
18. There are two major contrasting concepts of
community organisation. Organismal and
Individualistic concepts. Real world is a complex
mixture of both.
19. Classification and ordination are both useful and
valid approaches in analysing community data.
20. Besides -diversity of a sample plot or
community, there is -diversity (between-habitat
or between-community diversity), -diversity
(landscape diversity, product of  and diversity), -diversity (between landscape), and e
(regional diversity).
21. Community ecology is the study of the
community level of organisation, rather than the
study of clearly definable spatial and temporal
units. It is concerned with the structure and
function of multi-species assemblages, usually,
but not always, at one point in space and time.
22. It is not necessary to have sharp discrete
boundaries between communities to study
community ecology.
Ecological and Environmental
Change Research Group (EECRG)
One of the largest research groups in the Department of
Biology
Active in plant and animal ecological research,
publication, teaching, supervision of PhD and MSc
students, and studies in developing countries
MSc research in Norway, Svalbard, Tibet, Nepal, and
Uganda
Many MSc topics relate to Lectures 1, 2, 5, 7-10
Colloquia for this part of Bio-201 led by Tessa Bargmann,
an EECRG member
For further details, see www.eecrg.uib.no
EECRG Research Topics in this Lecture
Disturbance and diversity in several communities
in Norway, Nepal, Svalbard, and Scotland
Diversity studies in several vegetation types in
several countries
Ordination and gradient analysis of vegetation
and faunal assemblages
Relationships between , , , , and e diversity
(additive or multiplicative)
www.eecrg.uib.no