Interactions

1
Interactions

• Populations do not exist in isolation.
• All populations are tightly linked to other
  populationsthat share the same habitat.
• Categories of interaction
• parasitism /-
• predation /-
• herbivory /-
• competition -/-
• mutualism /

2
Parasitism

• Parasites are extremely diverse. (Fig. 49.1)
• All parasites acquire resources from their
  host.This is always detrimental to the host.
  (Fig. 49.2)
• A coevolutionary arms race exists between
  parasitesand their hosts.
• Parasites develop better ways to attack and use
  the host,while hosts develop better defenses.
• Example Plasmodium and the human immune system.
  (Fig. 49.3a,b)
• Parasites can manipulate the behavior of their
  host.(Fig. 49.4)

3
Figure 49.1 left
159 nm
4
Figure 49.1 middle
1437 nm
5
Figure 49.1 right
833 µm
6
Figure 49.2
2. Sporozoites reproduce asexually to form
merozoites in human liver.
8. After meiosis, resulting cells develop into
sporozoites and migrate to salivary glands.
3. Merozoites are released into blood- stream
where they infect red blood cells.
6. When a mosquito bites the human host,
gametocytes enter the mosquito as part of a
blood meal.
5. Merozoites surviving human immune system
become male or female gametocytes.
7
Figure 49.3a
1. Healthy liver cell has an HLA-B53 protein
on its membrane.
2. HLA-B53 protein displays cp26 protein from
Plasmodium, indicating that the liver cell is
infected.
4. Cytotoxic T cell kills liver cell before
merozoites are produced.
3. Cytotoxic T cell recognizes HLA-B53 and cp26
complex.
8
Figure 49.3b
In The Gambia, West Africa, different strains of
Plasmodium have different versionsof the cp
protein. How successful are these different
strains at infecting people?
Infectionrate
Plasmodiumstrain
Interpretation
cp26
Low
HLA-B53 binds to these proteins.Immune response
is effective.
cp29
Low
Immune response fails when thesestrains infect
the same person.
cp26 and cp29strains together
High
cp27
High
HLA-B53 does not bind to theseproteins. Immune
response is notas effective.
cp28
Average
9
Figure 49.4
Birds that prey on snails arethe next host for
the parasite
Infected snails move to opensunny areas
tentacles wiggle.
Uninfected snails stay in shadedareas tentacles
do not wiggle.
10
Predation

• When predation occurs, a predator kills and
  consumesa prey individual.
• Predators can regulate prey populations and/or
  reducethem to below carrying capacity. (Fig.
  49.5a,b)
• Prey have a wide array of mechanisms that they
  use todefend themselves from predation. (Fig.
  49.7)
• Keystone predators are those that have an
  exceptionallygreat impact on all the other
  surrounding species. (Fig. 49.9, 49.10)

11
Figure 49.5a
Regulated prey population
Carrying capacity (the max that can be
supported by available resources)
Prey population size
Population fluctuates within a narrow range
Time
12
Figure 49.5b
Predator behavior
Prey population size
Time
13
Figure 49.6
20
15
Predation rate (number of moosekilled/moose
density)
10
5
0
High
Medium
Low
Moose density
14
Figure 49.7 upper
Camouflage
15
Figure 49.7 center
Mimicry
16
Figure 49.7 lower
Weapons
17
Figure 49.8a
Prey and predator
18
Figure 49.8b
Correlation between predation rate and prey
defense
Attachment strength (N)
Shell mass (g)
Low predation
High predation
High predation
Low predation
Site type
Site type
19
Figure 49.8c
Is prey defense induced by presence of predator?
Are mussel defenses induced by the presence of
crabs?
Are mussel defenses induced by the presence of
broken mussel shells?
Seawater
Seawater
Broken mussel shells
Crab (fed fish, not mussels)
Intact mussel shells
No crab
Mussels
Mussels
Mussels
Mussels
Shell thickness HIGH
Shell thickness LOW
Shell thickness HIGH
Shell thickness LOW
Yes
Yes
20
Figure 49.9 left
Keystone predator present
21
Figure 49.9 right
Keystone predator absent
22
Figure 49.10 left
Keystone predator present
23
Figure 49.10 right
Keystone predator absent
24
Herbivory

• Unlike predators, herbivores are plant-eaters
  that removetissue from their prey, but rarely
  kill them.
• Why dont herbivores eat more of the available
  plantsthan they do?
• Top-down hypothesis (Fig. 49.11)
• Poor nutrition hypothesis
• Plant defense hypothesis (Fig. 49.12)

25
Figure 49.11
Predator
Herbivore
Primary producer(plants)
26
Competition

• Competition is detrimental to both of the
  individuals orspecies involved because it
  reduces available resources.
• Every species has a unique niche, or set of
  habitat requirements.
• Competition occurs when niches overlap.
• Competitive exclusion results when niches
  completely overlap. (Fig. 49.13c)
• Coexistence is possible if niches do not overlap
  completelyand the species involved partition the
  available resources.(Fig. 49.13b)
• Coexistence is also possible if other factors
  serve to limit the better competitor in some way.

27
Figure 49.13a
One species eats seeds of one size range
Number consumed
Seed size
28
Figure 49.13b
Partial niche overlap competition for seeds
ofintermediate size
Species 2
Species 1
Number consumed
Seed size
29
Figure 49.13c
Complete niche overlap
Species 1 Strong competitor
Species 2 Weak competitor,driven to extinction
Number consumed
Seed size
30
Figure 49.14 upper left
Consumptive competition occurs when organisms
compete for the same resources. These trees are
competing for nitrogen and other nutrients.
31
Figure 49.14 upper right
Preemptive competition occurs when individuals
occupy space and prevent access to resources by
other individuals. The space preempted by these
barnacles is unavailable to competitors.
32
Figure 49.14 middle left
Overgrowth competition occurs when an organism
grows over another, blocking access to resources.
This large fern has overgrown other individuals
and is shading them.
33
Figure 49.14 middle right
Chemical competition occurs when one species
produces toxins that negatively affect another.
Note how few plants are growing under these
Salvia shrubs.
34
Figure 49.14 lower left
Territorial competition occurs when mobile
organisms protect a feeding or breeding
territory. These red-winged blackbirds are
displaying to each otherat a territorial
boundary.
35
Figure 49.14 lower left
Encounter competition occurs when organisms
interfere directly with each others access to
specific resources. Here, spotted hyenas and
vultures fight over a kill.
36
Figure 49.15a
Intertidal competitors
Chthamalusin upperintertidal zone
Mean tidal level
Balanusin lowerintertidal zone
37
Figure 49.15b
COMPETITION EXPERIMENT
1. Transplant rockscontaining youngChthamalus
tolower intertidal.
Upperintertidal
Lower intertidal
2. Let Balanuscolonize the rocks.
Chthamalus
Balanus
3. Remove Balanusfrom one-half ofeach
rock.Monitor survivalof Chthamaluson both
sides.
On which side of the rocks doChthamalus survive
better?
38
Figure 49.15c
Chthamalus survives better without competition.
100
Competitor present
80
Competitor present
60
Competitorabsent
40
Competitorabsent
20
0
Young Chthamalus
Older Chthamalus
39
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 self-interest.
• The costs and benefits of mutualism vary widely
  between partners, over time, and from one area to
  the next. (Fig. 49.16ac)

40
Figure 49.16b
Mutualism between fish
41
Figure 49.17a
Treehopper excreting honeydew, which is harvested
by ants
42
Figure 49.17b
Are ants beneficial to treehoppers?
1000 m2study plot
Plants withants
Plants withants removed
43
Figure 49.17c
Which treatment contained more treehoppers?
100
80
Plantswithants
60
Average number of youngtreehoppers per plant
Plantswithoutants
40
20
0
25
30
10
20
20
5
August
July