BIOS 6150: Ecology
Dr. Stephen Malcolm, Department of Biological Sciences
•  Week 13: Community
Structure.
•  Lecture summary:
•  What is a community:
•  Chapters 17 & 24 in Begon, et
al. (1996) 3rd ed.
•  Chapters 16 & 21 in 4th ed.
Pine forest, Sweden (Begon et al. 1996)
•  Species diversity.
•  Succession.
•  Patterns of community
structure.
BIOS 6150: Ecology - Dr. S. Malcolm. Week 13: Community structure
Beech forest, Scotland (Begon et al.1996)
Slide - 1
2. What is a community?:
•  The community is an assemblage of species
populations that occur together in space and
time.
•  Ecological interest is in:
•  How assemblages of species are distributed.
•  Ways in which interactions among species
influence group assembly.
•  Community-level properties of assemblages.
BIOS 6150: Ecology - Dr. S. Malcolm. Week 13: Community structure
Slide - 2
3. Community properties:
•  Collective properties:
•  Include species diversity, community biomass &
productivity.
•  Emergent properties:
•  Product of population-level processes such as
predation, herbivory, parasitism and mutualism.
•  Not evident from simply summing the
interactions:
•  Like limits to similarity of competing species or food
web stability when disturbed.
BIOS 6150: Ecology - Dr. S. Malcolm. Week 13: Community structure
Slide - 3
4. Nested hierarchy of habitats:
•  Recognition of community patterns has dominated
community ecology at different levels of scale (Fig. 16.2).
BIOS 6150: Ecology - Dr. S. Malcolm. Week 13: Community structure
Slide - 4
5. Species diversity:
•  Counting numbers
of species:
•  Ideally should be
exhaustive as in
Fig. 16.3 but is
comparable only if
based on similar
sampling effort
(time or area).
BIOS 6150: Ecology - Dr. S. Malcolm. Week 13: Community structure
Slide - 5
6. Diversity indices:
•  Simply counting species ignores rarity and
abundance of individuals within species.
•  Simpson's diversity index includes:
•  Richness:
•  Number of species
•  Equitability:
•  Proportion of individuals or biomass that each species
contributes to total in the sample.
•  D = 1/ΣPi2, (for i = 1 to S)
•  where Pi is proportion of numbers or biomass contribution by
ith species to the total number of species (S) in the community
sample (richness).
BIOS 6150: Ecology - Dr. S. Malcolm. Week 13: Community structure
Slide - 6
7. Change in Shannon index with time:
•  Fig. 16.4: Species diversity (H) and equitability (J) of control
and fertilized plots in Rothamsted ‘parkgrass’ experiment.
BIOS 6150: Ecology - Dr. S. Malcolm. Week 13: Community structure
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8. Rank abundance
plots:
•  Relationship between
equitability and
richness (Fig. 16.5)
with full array of
ranked Pi values.
•  (a, b) rank-abundance
patterns of different
models; (c) change in
Rothamsted
grassland with
continuous fertilizer
application.
BIOS 6150: Ecology - Dr. S. Malcolm. Week 13: Community structure
Slide - 8
9. Community
patterns in space:
•  1. Gradient
analysis:
•  Distribution of
species (Fig.
16.6) according
to abiotic
conditions
(overlap in
abundances over
gradients, not
sharp
boundaries).
BIOS 6150: Ecology - Dr. S. Malcolm. Week 13: Community structure
Slide - 9
10. Distribution gradients:
•  Fig. 17.6 (3rd ed.): (a) grasses along pH gradient,
(b) macrofauna in oyster bed.
BIOS 6150: Ecology - Dr. S. Malcolm. Week 13: Community structure
Slide - 10
11. Community patterns in space
•  2. Ordination:
•  Organization of
communities by both
species composition &
relative abundance
(Fig. 17.7, 3rd ed.):
•  Examine patterns and
correlations to develop
hypotheses and
controlled experiments
to determine what
processes most
contribute to these
patterns.
BIOS 6150: Ecology - Dr. S. Malcolm. Week 13: Community structure
Slide - 11
12. Community
patterns in space
•  3. Classification:
•  Organization by
similarity (Fig. 17.8)
•  see Fig 16.7 in 4th ed.
•  Both ordination
and classification
are objective and
help to understand
community
associations and
perturbations.
BIOS 6150: Ecology - Dr. S. Malcolm. Week 13: Community structure
Slide - 12
13. Community patterns in time Succession:
•  Begon et al., (p 479) define succession as:
•  “the nonseasonal, directional and
continuous pattern of colonization and
extinction on a site by species populations.”
•  Succession describes the process of community
change from:
•  Colonization of a new habitat (e.g. sandbar, volcanic island,
etc.) by the “pioneer community”, to,
•  Steady state called a “climax community”, in which
changes occur continually but they tend to perpetuate the
same community structure rather than alter it.
BIOS 6150: Ecology - Dr. S. Malcolm. Week 13: Community structure
Slide - 13
14. Classification of successional
sequences within communities:
•  Degradative
Succession:
•  Occurs over
short time
scales via
heterotrophic
organisms
exploiting units
of dead organic
matter (feces,
carrion, detritus
etc.) until the
resource is
completely
utilized:
•  Fig. 17.9 (3rd
ed.).
BIOS 6150: Ecology - Dr. S. Malcolm. Week 13: Community structure
Slide - 14
15. Classification of successional
sequences within communities
•  Allogenic
Succession:
•  Result of
changing,
external
geophysicochemical
forces which
alter conditions
(abiotic) such
as silt
deposition in
estuaries and
marshes (Fig.
17.10, 3rd ed.)
BIOS 6150: Ecology - Dr. S. Malcolm. Week 13: Community structure
Slide - 15
16. Classification of successional
sequences within communities
•  Autogenic Succession:
•  Result of internal biological processes which can modify both
conditions and resources (biotic).
•  Primary (new habitat, e.g. after glacial retreat - Fig. 17.11, 3rd), or,
•  Secondary (e.g. old field after agricultural abandonment).
BIOS 6150: Ecology - Dr. S. Malcolm. Week 13: Community structure
Slide - 16
17. Secondary, autogenic succession:
•  Fig. 17.12 (3rd ed.): Marine algal colonization of concrete blocks
BIOS 6150: Ecology - Dr. S. Malcolm. Week 13: Community structure
Slide - 17
18. Secondary, autogenic succession:
•  Fig. 17.13 (3rd ed.): (a) Effect of removal of Ulva on Gigartina
recruitment; (b) Algal survivorship curves.
BIOS 6150: Ecology - Dr. S. Malcolm. Week 13: Community structure
Slide - 18
19. Old field secondary, autogenic
succession
Annual
weeds
Herbaceous
perennials
Shrubs
• Fugitives.
• Germinate under high
light intensity.
• Shade intolerant.
• r-selected.
BIOS 6150: Ecology - Dr. S. Malcolm. Week 13: Community structure
Early success
-ional trees
Late success
-ional trees
• Germinate under low
light intensity.
• Shade tolerant.
• K-selected.
Slide - 19
20.
Life history
characteristics
of early and
late successional plants
(Table 17.4,
3rd ed.):
BIOS 6150: Ecology - Dr. S. Malcolm. Week 13: Community structure
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21. Community
changes with time:
•  Fig. 17.15 (3rd ed.):
•  Changes with time
since abandonment of old fields.
(a) bare soil,
(b) annuals,
(c) herbaceous
perennials,
(d) woody plants,
(e) change in soil
nitrogen.
BIOS 6150: Ecology - Dr. S. Malcolm. Week 13: Community structure
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22. Tilman’s resource-ratio hypothesis
of succession (Fig. 16.14):
BIOS 6150: Ecology - Dr. S. Malcolm. Week 13: Community structure
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23. Three successional mechanisms:
•  Facilitation:
•  Early species make habitat more suitable for
new species.
•  Tolerance:
•  Different species exploit resources in different
ways.
•  Inhibition:
•  Invasions resisted by habitat modification:
•  e.g. allelopathy.
BIOS 6150: Ecology - Dr. S. Malcolm. Week 13: Community structure
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24.
Connell &
Slatyer’s
overview of
successional
mechanisms
(Fig. 17.16,
3rd ed.):
BIOS 6150: Ecology - Dr. S. Malcolm. Week 13: Community structure
Slide - 24
25. Simple patterns in community
structure:
•  Why do some communities contain more
species than others?
•  Are there patterns or gradients of species
richness?
•  If so, what are the reasons for these
patterns?
•  “Geographical”, “Climatic”, “Independent”
and “Biological” reasons.
BIOS 6150: Ecology - Dr. S. Malcolm. Week 13: Community structure
Slide - 25
26. Species richness
& resource
availability:
•  Richness related
to resource
availability axis
(R) as in Fig. 21.1
that is partitioned
(saturated)
according to niche
breadths (n) that
overlap by varying
amounts (o) as a
measure of
specialization.
BIOS 6150: Ecology - Dr. S. Malcolm. Week 13: Community structure
Slide - 26
27. Dr Seuss, nitches
and nutches:
Geisel, T.S. (“Dr. Seuss”) 1955. On beyond
Zebra. Random House Publishing, New
York.
http://shade.grove.iup.edu/~rgendron/Seuss.htmlx
BIOS 6150: Ecology - Dr. S. Malcolm. Week 13: Community structure
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28. Richness relationships:
•  Resource productivity more productive
environments have
more species (Fig.
24.2, 3rd ed.) with
narrower niches but
higher densities.
BIOS 6150: Ecology - Dr. S. Malcolm. Week 13: Community structure
Slide - 28
29. North American tree species richness
(Fig. 24.3) (see Fig 21.3 in 4th ed):
BIOS 6150: Ecology - Dr. S. Malcolm. Week 13: Community structure
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30.
North American
animal richness
relationships with tree
species richness (a-d)
and potential
evapotranspiration
(e-h) (Fig. 24.4, see
Fig. 21.4 in 4th ed.):
BIOS 6150: Ecology - Dr. S. Malcolm. Week 13: Community structure
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31. North American richness relationships
(Fig. 24.5, 3rd ed.):
Ants & rodents
BIOS 6150: Ecology - Dr. S. Malcolm. Week 13: Community structure
Lizards
Chydorid cladocera
Slide - 31
32. Highest richness at intermediate productivity
in some communities (Fig. 24.6, 3rd ed.):
BIOS 6150: Ecology - Dr. S. Malcolm. Week 13: Community structure
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33. Effect of spatial
heterogeneity:
•  Increased spatial
heterogeneity also
generates more
species diversity
(Fig. 24.8, 3rd ed.).
BIOS 6150: Ecology - Dr. S. Malcolm. Week 13: Community structure
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34. Species diversity and habitat structural diversity for (a)
fish in Wisconsin lakes and (b) birds (Fig. 24.9, 3rd ed.):
BIOS 6150: Ecology - Dr. S. Malcolm. Week 13: Community structure
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35. Lizard richness against desert plant
measures (Fig. 24.10, 3rd ed.):
BIOS 6150: Ecology - Dr. S. Malcolm. Week 13: Community structure
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36. Effect of climatic variation:
•  Unpredictable climatic variation is a form of disturbance and
species richness may be highest at intermediate levels.
•  But some work shows that species richness increases as
climatic variation decreases (Fig. 21.9).
BIOS 6150: Ecology - Dr. S. Malcolm. Week 13: Community structure
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37. Gradients of richness:
•  Latitude:
•  Increase in species
diversity with a decrease in
latitude towards the tropics
(Fig. 24.13, 3rd ed.).
•  Perhaps because of more
intense predation (topdown) and also reduced
competition, as well as
increased productivity
(bottom-up) but with most
productivity locked up in
biomass releasable by high
decomposition rates after
death.
BIOS 6150: Ecology - Dr. S. Malcolm. Week 13: Community structure
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38. Gradients of richness:
•  Altitude:
•  Decrease in species richness with increased altitude (Fig. 24.17, 3rd ed.).
BIOS 6150: Ecology - Dr. S. Malcolm. Week 13: Community structure
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39. Gradients of richness:
•  Depth:
•  Generally species richness in lakes decreases with water depth.
•  But for benthic invertebrates richness is highest on the continental shelf
at about 2000m (Fig. 24.19, 3rd ed.).
BIOS 6150: Ecology - Dr. S. Malcolm. Week 13: Community structure
Slide - 39
40. Gradients of richness:
•  Succession:
•  Species richness
increases with
time through
successional
series because
of a shift in
dominance (Fig.
24.20, 3rd ed.)
from smaller
numbers of
dominant
species to more
species of
equivalent
dominance.
BIOS 6150: Ecology - Dr. S. Malcolm. Week 13: Community structure
Slide - 40
41. Gradients of richness:
•  Succession:
•  Decline in richness at successional maturity (Fig. 24.21, 3rd ed.).
BIOS 6150: Ecology - Dr. S. Malcolm. Week 13: Community structure
Slide - 41