species interactions. interactions n populations do not exist in isolation. n all populations are...
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Interactions
Populations do not exist in isolation.
All populations are tightly linked to other populationsthat share the same habitat.
Parasitism
Parasites are extremely diverse.
All parasites acquire resources from their host.This is always detrimental to the host. 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)
Human host1. Sporozoites are injected from salivary gland of mosquito into human.
2. Sporozoites reproduce asexually to form merozoites in human liver.
3. Merozoites are released into blood- stream where they infect red blood cells.
5. Merozoites surviving human immune system become male or female gametocytes.
6. When a mosquito bites the human host, gametocytes enter the mosquito as part of a blood meal.
8. After meiosis, resulting cells develop into sporozoites and migrate to salivary glands.
Mosquito host
7. Male and female gametocytes fuse in mosquito’s gut.
GametocytesSporozoitesin salivaryglands
Gut
4. Merozoites reproduce asexually until they cause red blood cells to rupture (causing anemia in human host).
CytotoxicT cell
Infected liver cell
HUMAN IMMUNE DEFENSE AGAINST PLASMODIUM
Plasmodiumsporozoites
HLA-B53
Healthyliver cell
HLA-B53
Infected liver cell
cp26 proteinfrom Plasmodium
1. Healthy liver cell has an HLA-B53 protein on its membrane.
2. HLA-B53 proteindisplays cp26 protein from Plasmodium, indicating that the liver cell is infected.
3. Cytotoxic T cellrecognizes HLA-B53and cp26 complex.
4. Cytotoxic T cellkills liver cell before merozoitesare produced.
Dead liver cell
CytotoxicT cell
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
cp26 and cp29strains together
HighImmune response fails when thesestrains infect the same person.
HLA-B53 does not bind to theseproteins. Immune response is notas effective.
cp27
cp28
High
Average
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.
Predation
When predation occurs, a predator kills and consumesa prey individual.
Predators can regulate prey populations and/or reducethem to below carrying capacity.
Prey have a wide array of mechanisms that they use todefend themselves from predation.
Keystone predators are those that have an exceptionallygreat impact on all the other surrounding species.
Regulated prey population
Time
Population fluctuates within a narrow range
Carrying capacity
Pre
y p
op
ula
tio
n s
ize
15
20
10
Pre
dat
ion
rat
e (n
um
ber
of
mo
ose
kille
d/m
oo
se d
ensi
ty)
5
0
High Medium Low
Moose density
Correlation between predation rate and prey defense
Att
ach
men
t st
ren
gth
(N
)
Sh
ell m
ass
(g)
Low predation High predation High predationLow predation
Site type Site type
Is prey defense induced by presence of predator?
Are mussel defenses inducedby the presence of crabs?
Are mussel defenses induced by the presence of broken mussel shells?
Seawater Seawater
Crab(fed fish, not mussels)
Mussels Mussels Mussels Mussels
No crabBroken musselshells
Intact musselshells
Shell thickness HIGH Shell thickness LOW Shell thickness HIGH Shell thickness LOW
Yes Yes
Herbivory
Unlike predators, herbivores are plant-eaters that removetissue from their prey, but rarely kill them.
Competition Competition is detrimental to both of the individuals or
species 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.
• Coexistence is possible if niches do not overlap completelyand the species involved partition the available resources.
• Coexistence is also possible if other factors serve to limit the better competitor in some way.
Partial niche overlap: competition for seeds ofintermediate size
Species 1
Species 2
Nu
mb
er c
on
sum
ed
Seed size
Complete niche overlap
Species 1: Strong competitor
Species 2: Weak competitor,driven to extinction
Nu
mb
er c
on
sum
ed
Seed size
Consumptive competition occurs when organisms compete for the same resources. These trees are competing for nitrogen and other nutrients.
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.
Overgrowth competition occurs when an organism grows over another, blocking access to resources. This large fern has overgrown other individuals and is shading them.
Chemical competition occurs when one species produces toxins that negatively affect another. Note how few plants are growing under these Salvia shrubs.
Territorial competition occurs when mobile organisms protect a feeding or breeding territory. These red-winged blackbirds are displaying to each otherat a territorial boundary.
Encounter competition occurs when organisms interfere directly with each other’s access to specific resources. Here, spotted hyenas and vultures fight over a kill.
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.