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Patterns of diversity/
Landscape ecology
Ruesink Lecture 7
Biology 356
What does this course cover?
Week 9, 10
Landscapes:
Week 8
Week 5-7
Week 2
Week 3, 4
Week 1, 2
Fig 1.1
Patterns in the
distribution and
abundance of species
• Depend on history
• Abiotic conditions
• Biotic interactions
• Each step is a “filter”
helping to determine
local community
structure
Which species can
survive the local
physical
conditions?
Which species eat
or outcompete
others?
• Regional pool of
species depends on
evolutionary history
• The activity space of
species determines
their response to
abiotic conditions
• Species interactions
influence local
distribution and
abundance
Which species can
survive the local
physical
conditions?
Which species eat
or outcompete
others?
Which system has higher
species richness?
Which system has higher
species diversity?
Which system has higher
species richness?
Which system has higher
species diversity?
More diverse because
species have more even
abundances!!!
Patterns of diversity
• Species richness varies with latitude
• Species richness varies with altitude
• Hotspots of diversity contain many
endemic species
Latitudinal diversity gradient:
Birds from the new world
(Gaston & Blackburn, 2000. Pattern
and Processes in Macroecology)
Figure 23.1
Figure 23.2: North American mammals
Habitat
heterogeneity
also influences
diversity
Some reasons for latitudinal
diversity gradients:
• Area
boreal
23%
tundra
2%
tropical
40%
temperate
19%
subtropical
16%
(Rosenzweig, 1992. Journal of Mammalogy)
Some reasons for latitudinal
diversity gradients:
• Area
• Energy: higher, nonseasonal productivity allows
multiple species to coexist (more action at the
base of the food web)
Some reasons for latitudinal
diversity gradients:
• Area
• Energy: higher, nonseasonal productivity allows
multiple species to coexist (more action at the
base of the food web)
• Statistical artifact: species ranges thrown at
random onto the globe will concentrate in the
“mid-domain”
…testing diversity?
Species richness
Control
Treatment 1: addition of species at the poles
90 N
0
90 S
Latitude (degrees)
Treatment 2: addition of species at the equator
Some exceptions:
Some taxa are
adapted to life at
higher latitudes (e.g.
penguins and auks)
• Aphids, sawflies,
ichneumonids and bees:
show peaks at
intermediate or high
latitudes.
Other latitudinal gradients:
Range size
• Rapoport’s rule: the
tendency for species
living at higher latitudes
to have larger range
sizes
• Bergman’s rule: body
size increases towards
the poles
Figure 25.3: Hotspots
Endemic species are those found only in a single area
Value of biodiversity
• Utilitarian (of value to humans)
– Use value
• Goods
• Services (including recreation,
biogeochemical cycles)
– Existence value
• Intrinsic (of value to the species
itself)
Patterns of species loss
• Mass extinctions through geologic
time
• Modern mass extinction
Many mass extinctions were externally imposed. Up to
95% of species went extinct. Re-diversification required
millions of years.
dinosaurs
Figure 24.1a
Causes of endangerment for US species
Wilcove et al. 1998 Bioscience
Habitat transformation
is a leading cause of
endangerment and
extinction. Red =
agricultural “biome”
Modern extinction rates
• 100-1000 x background rates
• Based on habitat loss and speciesarea relationships
S = 30 x A0.33
S = 30 x A0.33
If A = 1, S = 30
If A = 0.1, S = 14
S = 30 x A0.33
Compare the relative
change in species for a
relative change in area.
More than half of the fern
species are expected to go
extinct
Biogeography
• Documents and understands spatial
patterns of biodiversity
• Biogeographic realms reflect
separate evolution in areas poorly
linked by dispersal
Figure 24.4
Figure 24.7
Figure 24.6
The modern era
• Homogocene?
• New Pangaea?
• Obscene?
Principle of convergence: similar adaptations occur in different
evolutionary lineages in similar habitats on different contintents
Figure 24.11
Figure 24.12a
Island biogeography
• Dynamic equilibrium theory that
explains species richness in patches
• Local richness reflects colonization
and extinction rates
Figure 23.14
Smaller islands (higher E) are expected
to have fewer species than larger islands
Figure 23.15
Far islands (lower C) are expected to have
fewer species than near islands
Figure 23.16
Figure 23.17
Experimental test of island
biogeography
• Defaunation experiment by
Simberloff and Wilson
• Methods:
– Survey small mangrove islands for
arthropods.
– Cover islands with plastic and spray with
insecticide.
– Observe colonization/ succession over
one year.
Figure 23.18
Results
• Species richness on islands returned
to levels similar to before
defaunation
• Closer, larger islands had more
species
• The precise species identity was not
consistent, only the total number of
species
New challenges in landscape
ecology
• Humans are creating increasingly
fragmented landscapes
• What are the consequences?
• What are effective methods of
protecting habitat?
Climate Change
MELTING SNOWS OF KILIMANJARO
Some scientists believe the snow cap of Mount Kilimanjaro will be
gone in two decades. Researchers say the ice fields on Africa’s
highest mountain shrank by 80 percent in the past century. The
snow cap formed some 11,000 years ago. The Landsat satellite
captured these images of Kilimanjaro February 17, 1993 and
February 21, 2000.
Roadless areas in
Cascadia
Example of landscape-level
change: Edge Effects
• Effects on species in addition to loss
of habitat
• Which species benefit?
• Which species lose?
Edge Effects
Patches
themselves are
heterogeneous
Dramatic examples of edge effects
Browse zones around patches in mussel beds
Birds have been intensively studied for edge
effects.
Brown-headed cowbird male. Brood parasite.
Invasive?
Experimental
nests (quail eggs)
preyed upon as a
function of
distance from
the forest edge
Biological Dynamics of Forest Fragments Project
1, 10, and 100 ha areas (and control areas within
intact forest)
Do species differ in terms of effects of fragmentation?
Does the matrix make a difference?
Does patch size make a difference?
Stouffer & Bierregaard 1995 Ecology
Why would birds that follow army ants be so sensitive
to fragmentation?
Mortality and damage
of trees in different
fragments, at
different distances
from the edge.
Laurance et al. 1998
Ecology
Edge Effects
• Promotes disturbance (blowdown)
• Interior specialists disappear from
small fragments
• Microclimate changes (and food)
• Nest predation and brood parasitism
• Habitat heterogeneity -> higher
diversity
End of lecture for lack of time!!!!