Download 7.014 Lectures 33,34,35 Species Interactions

7.014
Lectures 33,34,35
Species Interactions
May 5, 7, 10 2004
Types of Competition
Consumptive competition
Preemptive competition
Overgrowth competition
Chemical competition
Territorial competition
Encounter competition
1
The Fundamental Ecological Niche:
“An n-dimensional hyper-volume every point on which a species can
humidity
survive and reproduce indefinitely in the absence of other species”
(Hutchinson)
tem
per
atu
re
od
Fo
e
siz
The Realized Ecological Niche:
the niche actually occupied in the presence of other species
humidity
niche overlap leads to competition
tem
per
atu
re
od
Fo
e
siz
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Figure 49.13a
Number consumed
One species eats seeds of one size range
Seed size (one niche dimension
Figure 49.13b
Partial niche overlap:
competition for seeds of
intermediate size
Partial niche overlap can lead to
Niche Partitioning and
Competitive Coexistence
Species 2
Number consumed
Species 1
Seed size
3
Figure 49.13c
Complete niche overlap
Strong nice overlap can lead
to Competitive Exclusion
Number consumed
Species 1: Strong competitor
Species 2: Weak competitor,
driven to extinction
Seed size
The Spread of Introduced Zebra Mussels in the
United States (1998 – 2001)
Extensive
niche overlap
can lead to
competitive
exclusion
4
Figure 49.15a
Observed Distributions
Chthamalus
in upper
intertidal zone
Mean tidal level
Balanus
in lower
intertidal zone
Figure 49.15b
COMPETITION EXPERIMENT
Upper
intertidal
1. Transplant rocks
containing young
Chthamalus to
lower intertidal.
Lower intertidal
2. Let Balanus
colonize the rocks.
Chthamalus
Balanus
3. Remove Balanus
from one-half of
each rock.
Monitor survival
of Chthamalus
on both sides.
On which side of the rocks do
Chthamalus survive better?
5
Chthamalus survives better without competition.
100
Competitor present
Percent mortality
80
Competitor present
60
Competitor
absent
40
Competitor
absent
20
0
Young Chthamalus
Older Chthamalus
Figure 49.15c
Larval
Settlement
Zone
Larval
Adult
Settlement
Distribution
Zone
Spring high tide
Adult
Fundamental
Distribution Niche
Neap high tide
Could not
become adults
due to
competition
Barnacles
subject to
desiccation
Realized
Niche
Chthamalus
Mean tidal level
Balanus
Neap low tide
Spring low tide
Distribution of Two Barnacle Species – Balanus and Chthamalus
6
Niche Partitioning
can lead to
Adaptive
Radiation
ANCESTOR FINCH
Blue-back grassquit
Sharp-billed
ground finch
Vegetarian finch
Mangrove
finch
Small tree
finch
Large
cactus finch
Cactus finch
Large tree finch
Medium tree finch
Large
ground
finch
Woodpecker finch
Medium ground finch
Warbler finch
Insect Eaters
Bud Eaters
Seed Eaters
Galapagos Finches
Hawaiian
Honeycreepers
Adaptive Radiation to Exploit a Variety of Food
Sources Results in Speciation and a variety of
Beak Shapes
7
Stabilizing Selection
Medium-sized individuals favored
Number of
Individuals
with
phenotype
Reduces
Variation
0
10
20
30
40
50
Peak gets higher and narrower
Selection
Mean stays
the same
0
10
20
30
40
50
Directional Selection
Larger individuals favored
Number of
Individuals
with
phenotype
0
10
20
30
40
50
Peak shifts in one direction
Selection
Mean Shifts
0
10
20
30
40
50
8
Directional Selection
Large and small individuals favored
Number of
Individuals
with
phenotype
0
10
20
30
40
50
Two Peaks
Two populations
forming
Selection
30
40
50
African Seedcracker
(Pyrenestes ostrinus)
Birds with smaller bills
can consume soft
seeds more efficiently
Number of Birds
100
Birds with
intermediate beak
size survive
poorly
50
0
10
15
20
Birds with large
bills can crack
hard seeds
Competition can
lead to
character
displacement
Width of lower bill (mm)
9
Predation
Snowshoe Hare and Lynx Population Population Cycles
Number of Pelts (thousands)
Lepus americaus
Lynx canadensis
Hudson Bay Company Trapping Records
150
(1840 –1940)
Hare
100
Lynx
11 years
50
1840
1870
1900
1930
What drives the oscillation?
10
Field Experiments - Lloyd Keith (1960’s to 1980’s)
What accounts for population cycles?
Food Supply or Predation?
5
Food Supply Increased
Ratio of Hare Density to Controls
3
1
5
Predators Excluded
3
1
15
13
Food Supply Increased &
Predators Excluded
11
CONCLUSION:
9
5
3
Food Supply & Predation both
affect population cycles.
1
Control
Phase of Hare Population
Predatory mite
Prey mite
prey
Source: Ricklefs, R. The Economy of Nature 3rd Ed., p.372
11
Evidence for predation as
an evolutionary agent:
-
Cryptic Coloration
- Physical and Chemical Defenses
- Mimicry
Figure 49.12b
20
Resprouted trees have more defense compounds.
Salicortin concentration
(mg/g dry mass)
15
10
5
0
Control
trees
Browsed and
resprouted trees
12
Figure 49.12c
400
Herbivorous larvae have higher survivorship in the face of
their own predators (ants) when they have been feeding on
resprouted trees.
Thus --- Leaf beetle larvae sequester antibeaver compounds and use them as a
defense against ants
Larval survival time (sec)
300
200
100
0
Larvae from
browsed and
resprouted trees
Larvae from
control trees
Figure 49.8b
Shell mass (g)
Attachment strength (N)
Correlation between predation rate and prey defense
Low predation
High predation
Site type
Low predation
High predation
Site type
13
Is prey defense induced by presence of predator?
Figure 49.8c
Are mussel defenses induced
by the presence of crabs?
Are mussel defenses induced by the
presence of broken mussel shells?
Seawater
Crab
(fed fish, not mussels)
Mussels
Shell thickness HIGH
Seawater
No crab
Broken mussel
shells
Intact mussel
shells
Mussels
Mussels
Mussels
Shell thickness LOW
Shell thickness HIGH
Yes
Shell thickness LOW
Yes
Mutualism
• Mutualism is a type of interaction that is
beneficial to both species involved.
• It does not involve altruism. The benefits are
a by-product of each species’ own selfinterest.
• The costs and benefits of mutualism vary
widely between partners, over time, and from
one area to the next.
(Fig. 49.16a–c)
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