BIOS 3010: Ecology
Lecture 23: Patterns of Biodiversity & conservation:
Male Passenger Pigeon
•  Lecture summary:
–  Patterns of diversity.
–  Richness relationships &
gradients:
•
•
•
•
•
Resource productivity.
Spatial heterogeneity.
Climate.
Latitude, altitude & depth.
Succession.
–  Conservation.
•  Counting species.
•  Threats, Uncertainty & Risk.
•  Population Viability Analysis.
Dr. S. Malcolm
BIOS 3010: Ecology
Lecture 23: slide 1
2. Simple patterns:
•  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.
–  Species richness (number of species present at a site)
can be related to a 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.
Dr. S. Malcolm
BIOS 3010: Ecology
Lecture 23: slide 2
3. Richness relationships:
•  Resource productivity:
–  More productive environments have more
species with narrower niches but higher
densities (Fig. 24.2).
–  But evidence also suggests that highest diversity
occurs at intermediate levels of productivity in
some communities (Fig. 24.6) because
competitive exclusion is less likely and
immigration rates are higher.
Dr. S. Malcolm
BIOS 3010: Ecology
Lecture 23: slide 3
1
4. Richness relationships:
•  Increased spatial heterogeneity also
generates more species diversity
(Fig. 24.9).
•  Climatic variation influences species richness:
–  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).
Dr. S. Malcolm
BIOS 3010: Ecology
Lecture 23: slide 4
5. Gradients of richness:
•  Latitude:
–  Increase in species diversity with a decrease in
latitude towards the tropics (Fig. 24.13).
•  Perhaps because of more intense predation (top-down)
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.
•  Altitude:
–  Decrease in species richness with increased
altitude (Fig. 24.17).
Dr. S. Malcolm
BIOS 3010: Ecology
Lecture 23: slide 5
6. 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).
•  Succession:
–  Species richness increases with time through
successional series because of a shift in dominance
(Fig. 24.20) from smaller numbers of dominant species
to more species of equivalent dominance.
•  Then usually a decline in richness at successional maturity
(Fig. 24.21).
Dr. S. Malcolm
BIOS 3010: Ecology
Lecture 23: slide 6
2
7. Conservation ecology
•  The need for conservation:
– As human population density has increased
worldwide, extinctions of other species
have increased for the following reasons:
•  Overexploitation by hunting and harvesting.
•  Habitat destruction.
•  Introduction of exotic pest species.
•  Pollution.
Dr. S. Malcolm
BIOS 3010: Ecology
Lecture 23: slide 7
8. The need for conservation:
•  Extinctions impact biodiversity
–  Species richness:
•  Number of species in a geographical area.
–  Species diversity:
•  Species richness + relative species abundances,
biomasses or productivities.
–  Scale of ecological organization:
•  From genes and populations through communities to
landscapes and biomes.
•  Fig. 7.16 and Table 7.4.
Dr. S. Malcolm
BIOS 3010: Ecology
Lecture 23: slide 8
9. The basic conservation problem:
•  Realistically, the only viable way to conserve
species and habitats is to address the
issue politically through economics driving
legislation:
–  This is a good example of Garrett Hardin s class
of no technical solution problems in which
science can explain the problem but cannot
solve it:
•  Solutions are implemented through legislation.
Dr. S. Malcolm
BIOS 3010: Ecology
Lecture 23: slide 9
3
10. The basic conservation problem:
•  The problem is how to assess the economic
value of species and habitats (ecological
economics).
•  We need to assess:
–  (1) Direct economic value through conserved
resource consumption (objective).
–  (2) Indirect economic value, including amenity
value without the need for resource
consumption (objective).
–  (3) Ethical value of species (subjective).
Dr. S. Malcolm
BIOS 3010: Ecology
Lecture 23: slide 10
11. Counting species:
•
•
•
•
How do we count the number of species alive today?
Needed to estimate rates of extinction (Table 7.4).
About 1.8 million species have been named.
Estimates of how many exist are based on:
–  2 tropical species for each temperate species:
•  = 3-5 million species.
–  Rate of discovery of new species, group by group:
•  = 6-7 million species.
–  Species size:species richness relationship >0.2 mm:
•  = 10 million species.
–  Ratio of beetle:non-beetle species richness:
•  = 30 million tropical arthropod species:
–  but see Zuckerman in the 9 June 2010 issue of New Scientist at:
http://www.newscientist.com/article/dn19019-global-biodiversity-estimate-revised-down.html
–  Estimates go as high as 80 million species.
Dr. S. Malcolm
BIOS 3010: Ecology
Lecture 23: slide 11
12. Threats to species:
•  Rarity (Fig. 7.17) - categories of threat:
–  Vulnerable:
•  10% probability of extinction within 100 years.
–  Endangered:
•  20 % probability of extinction within 20 years or 10
generations (whichever is longer).
–  Critical:
•  50% probability of extinction within 5 years or 2
generations.
Dr. S. Malcolm
BIOS 3010: Ecology
Lecture 23: slide 12
4
13. Threats to species:
•  Both prevalence (proportion area covered
by a species) and intensity (density) are
important.
•  Absence can be just as important as
presence for different spatial and
temporal distributions.
•  8 types of commonness or rarity:
–  (Table 25.2).
•  Abundance and distribution appear to be
positively correlated (Fig. 25.3).
Dr. S. Malcolm
BIOS 3010: Ecology
Lecture 23: slide 13
14. Threats to species:
•  Overexploitation:
–  Unsustainable harvests of resources such as great
whales and large terrestrial herbivores (bison).
–  Collection of rare species.
•  Habitat disruption:
–  Through destruction, degradation or disturbance.
•  Introduced species:
–  e.g. brown tree-snake on Guam or the nile perch in
Lake Victoria (Fig. 25.4).
Dr. S. Malcolm
BIOS 3010: Ecology
Lecture 23: slide 14
15. Uncertainty and the risk of extinction:
•  Dynamics of small populations: (Fig. 7.18).
–  High levels of uncertainty and high risks of
extinction through:
•  (1) Demographic uncertainty
•  (2) Environmental uncertainty
•  (3) Spatial uncertainty (metapopulations).
•  Local and global extinctions:
–  Local extinctions are common events (Fig. 7.21)
and extinction is more likely in smaller
populations.
Dr. S. Malcolm
BIOS 3010: Ecology
Lecture 23: slide 15
5
16. Uncertainty and the risk of extinction:
•  Habitat fragmentation:
–  Populations fragment into metapopulations.
–  Then each constituent subpopulation gets smaller
with higher risks of extinction (Fig. 25.9).
–  Fragmentation thus influences the probability of
extinction of metapopulations and the way in
which we design nature reserves
(Figs. 25.11 & 25.12).
Dr. S. Malcolm
BIOS 3010: Ecology
Lecture 23: slide 16
17. Population Viability Analysis (PVA):
•  What is the minimum viable population size (MVP) for a
species population?
•  Answers based on:
–  (1) Clues from long-term studies:
•  e.g. Fig. 25.8b using criteria such as 95% probability of
persistence for 100 years (Table 7.6)
•  Based on data from hunting and bird watching enthusiasts.
–  (2) Subjective assessment:
•  Discussion among experts on target species to develop PVAbased decision analysis for species such as the Sumatran
rhinoceros (Fig. 7.23).
–  (3) Modelling persistence time:
•  Increases with population size and mean intrinsic rate of
natural increase - if mean r is greater than its variance then
persistence time increases dramatically (Fig. 7.24, 7.26).
Dr. S. Malcolm
BIOS 3010: Ecology
Lecture 23: slide 17
BIOS 3010: Ecology
Lecture 23: slide 18
Figure 21.1:
Simple model of
how species
richness may vary
with resource
range (R), niche
size (n), and niche
overlap (o)
Dr. S. Malcolm
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Figure 24.2 (3rd ed.): Niche overlap and
environmental productivity.
Dr. S. Malcolm
BIOS 3010: Ecology
Lecture 23: slide 19
Figure 24.5 (3rd ed.): Species richness of (a) seed-eating
rodents and ants (b) lizards, and (c) cladocera,
against measures of productivity.
Dr. S. Malcolm
BIOS 3010: Ecology
Lecture 23: slide 20
Figure 24.6 (3rd ed.) : Highest richness at intermediate
levels of productivity for (a) Malaysian trees, (b)
fynbos plants, (c) desert rodents.
Dr. S. Malcolm
BIOS 3010: Ecology
Lecture 23: slide 21
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Figure 24.9 (3rd ed.) : Increase in species richness with
increased spatial heterogeneity for (a) freshwater fish in
Wisconsin lakes, and (b) birds in Mediterranean climates.
Dr. S. Malcolm
BIOS 3010: Ecology
Lecture 23: slide 22
Figure 21.9: Decreasing species richness with increased
temperature ranges in western North America.
Dr. S. Malcolm
BIOS 3010: Ecology
Lecture 23: slide 23
Figure 24.13
(3rd ed.) : Variation in species richness
with latitude (see fig. 21.21, 4th ed.).
Dr. S. Malcolm
BIOS 3010: Ecology
Lecture 23: slide 24
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Figure 24.17 (3rd ed.): Variation in species richness
with altitude in Nepal (see fig. 21.22, 4th ed.).
Dr. S. Malcolm
BIOS 3010: Ecology
Lecture 23: slide 25
Figure 24.19 (3rd ed.): Species richness with depth
of marine, bottom-dwelling animals.
Dr. S. Malcolm
BIOS 3010: Ecology
Lecture 23: slide 26
Figure 24.20 (3rd ed.): Rank-abundance curves of
successional shifts in species richness.
Dr. S. Malcolm
BIOS 3010: Ecology
Lecture 23: slide 27
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Figure 24.21 (3rd ed.): Increase in species richness
during old-field successions (see Fig. 21.25, 4th ed.)
Dr. S. Malcolm
BIOS 3010: Ecology
Lecture 23: slide 28
Figure 7.16: Trends in animal species
extinctions since 1600.
Dr. S. Malcolm
BIOS 3010: Ecology
Lecture 23: slide 29
BIOS 3010: Ecology
Lecture 23: slide 30
Table 7.4
Dr. S. Malcolm
10
Figure 7.17: Levels of threat.
Dr. S. Malcolm
BIOS 3010: Ecology
Lecture 23: slide 31
BIOS 3010: Ecology
Lecture 23: slide 32
Table 25.2 (3rd ed.):
Dr. S. Malcolm
Figure 25.3 (3rd ed.): Abundance positively correlated
with distribution of breeding birds in Britain.
Dr. S. Malcolm
BIOS 3010: Ecology
Lecture 23: slide 33
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Figure 25.4 (3rd ed.): Effect of brown tree
snake on forest birds of Guam.
Dr. S. Malcolm
BIOS 3010: Ecology
Lecture 23: slide 34
Figure 7.18: Path to extinction in small
populations.
Dr. S. Malcolm
BIOS 3010: Ecology
Lecture 23: slide 35
Figure 7.21: Extinction rates against habitat area for
(a) zooplankton in lakes, (b, c, e, f) birds on
islands, (d) plants in Sweden.
Dr. S. Malcolm
BIOS 3010: Ecology
Lecture 23: slide 36
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Figure 25.9
(3rd ed.):
Breeding success
of birds in
Michigan at
different
distances from a
forest edge.
Dr. S. Malcolm
BIOS 3010: Ecology
Lecture 23: slide 37
Figure 25.11 (3rd ed.): Extinction probabilities (P) for same
sized metapopulations subjected to different
degrees of fragmentation (m = migration).
Dr. S. Malcolm
BIOS 3010: Ecology
Lecture 23: slide 38
Figure 25.12 (3rd ed.): Abundance of checkerspot
butterflies in (a) a single population
or (b) 3 separate populations.
Dr. S. Malcolm
BIOS 3010: Ecology
Lecture 23: slide 39
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Figure 25.8 (3rd ed.): Extinction or persistence against
population size for (a) island birds, and (b) bighorn sheep.
(b = Fig 7.22 in 4th ed.)
Dr. S. Malcolm
BIOS 3010: Ecology
Lecture 23: slide 40
BIOS 3010: Ecology
Lecture 23: slide 41
Table 7.6:
Dr. S. Malcolm
Figure 7.23: 30-year management decisions for
Sumatran rhinoceros (pE = probability of
extinction, EpE = expected value of pE).
Dr. S. Malcolm
BIOS 3010: Ecology
Lecture 23: slide 42
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Figure 7.24: Population persistence time against
population size under demographic and
environmental stochasticity.
Dr. S. Malcolm
BIOS 3010: Ecology
Lecture 23: slide 43
Figure 7.26: Cumulative probability of elephant
extinction in 6 different habitat sizes over 1,000 years.
Dr. S. Malcolm
BIOS 3010: Ecology
Lecture 23: slide 44
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