Transcript Ecology: Lecture 1

Ecology: Lecture 16
Parasitism and Mutualism
Lecture overview
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Basics of parasitism
Characteristics of parasites
Hosts as habitat
Life cycles
Dynamics of transmission
Host responses
Basics of parasitism
 Defined: Condition whereby two
organisms live closely together and one
derives its nourishment (or other resource)
at the expense of the other.
 Impacts on individuals
 How do parasites affect their hosts?
 What determines the degree of impact?
Basics of parasitism
 Impacts on populations
 What did early ecologists think about the
role of parasites?
 What did Aldo Leopold hypothesize?
 Current: Many studies show effects of
parasites on
 Host’s birth, death and growth rates
 Host’s mating success
 Host’s susceptibility to predation
Characteristics of parasites
 Key groups of parasites
 Micro vs. macroparasites
 Location of parasites
 Ectoparasites: outside, may
burrow (i.e.ticks, fleas, gill
parasites)
 Endoparasites: live inside
body (i.e. tapeworms)
British Broadcasting Company (BBC)
Parasitoids
 Intermediate between predators and
parasites
 Eventually kill their host, but it takes many to
kill one (and only one…)
Parasitoid wasps on
caterpillar
WSU Cooperative Extension
Hosts as habitat
Location as related to needs/strategies
 Trematode parasites in
snail gonads
 Lipid-rich environment!
Photos: USGS “Soundwave” program
Hosts as habitat
Location as related to needs/strategies
 Tapeworms in
digestive tract
 Absorbs ready-touse nutrients!
 No digestive tract
of its own
Hosts as habitat
Location as related to needs/strategies
 Schistosoma “blood fluke” in intestinal
blood vessels
 Direct access to nutrients
 Location by intestine: eggs released into intestine/exit
with feces
University of York
Department of Biology
Host entry
 Via food and drink
 Trichinosis: Eating raw
or undercooked pork
 Cholera: contaminated
water supply and food
Campbell, Reese “Biology”
M. Courtney-Clarke,
Photo Researchers, Inc.
Host entry
 Via burrowing
 Schistosoma mansoni
burrows through feet
or ankles of wading
person
Host entry
 Via insect bite
 Plasmodium, the
malaria parasite, enters
from the salivary
glands of the mosquito
into the bloodstream
www.solcomhouse.com
www.membranetransport.org
Host entry: Candiru
 Via body passageways…
Host exit
 Via the feces
 Schistosoma mansoni
Host exit: bot fly
Host entry
 Via insect bite
 Malaria: A few
Plasmodium in,
many Plasmodium
out…
www.solcomhouse.com
www.membranetransport.org
Life cycle: single host
“Direct transmission”
 Single host; may exit host
 Mechanisms of transfer
 Direct host-to-host contact (lice)
 Bites (rabies)
 Vectors: transfers parasite from host to host
 Example: Bot fly uses mosquito vector for transfer
to mammalian host… Mosquito not infected.
 NOTE: For malaria, the mosquito is infected; it is a
secondary host as well as a vector.
Life cycle: multiple hosts
“Indirect transmission”
 Human
 Definitive host:
location of sexual
reproduction
 Snail
 Intermediate host:
asexual reproduction
only
 See outline and own notes
for more detail
Dynamics of transmission
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Direct transmission tends to favor
high population densities.
Exception: introduced parasites may
initially spread rapidly due to lack of
developed defenses.
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In these cases, high rate of spread may be
independent of density
Dynamics of transmission
 Multiple host parasites: Success
linked to
 Effectiveness of transfer
 Availability of both species to complete life
cycle
Dynamics of transmission
Advantages of multiple hosts
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One host scarce; parasite can persist in other host
Both asexual and sexual reproduction occur
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Why an advantage to have both types?
Disadvantages of multiple hosts
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Disruption of transmission prevents completion of
life cycle
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Schistosomiasis can be prevented by wearing waders
Loss of one host  eventual crash of the parasite
population.
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Eradication of mosquitoes reduces malaria.
Host response to parasitism
Biochemical
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Inflammation
Immune response
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In some cases, hosts can become resistant to the
parasite (Schistosomiasis)
Abnormal growths
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Cysts may form around the invading parasite
(Plant galls [Fig. 17.10])
Galls on plants
Host response to parasitism
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Sterility
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Example: parasite within snail gonad tissue
Also see text for nematode parasite in
fungus-eating flies.
Behavioral changes
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Example 1: Ant parasitized by the liver fluke
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Example 2: Killfish infected with a particular
trematode (fluke relative)
Dicrocoelium dendriticum
Mutualism (briefly)
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Defined: A relationship between two
species in which both benefit
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Types of mutualistic relationships
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Obligate symbiotic mutualism: a
permanent and obligatory relationship where
it is sometimes difficult to tell where one
organism ends and the other begins
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Example: coral animals and their protist
(zooxanthellae) symbionts
Obligate symbiotic mutualism:
coral reefs
Reef and coral photos courtesy of NOAA
Coral: a closer look
Mutualism
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A brief survey of mutualistic
relationships (cont.)
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Obligate non-symbiotic mutualism: two
organisms live physically separate lives, but
cannot survive without each other
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Non-obligatory (facultative) mutualism
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Example: Pollination (some cases)
Example: Seed dispersal by animals (sometimes)
Defensive mutualism
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Example: Alkaloid-producing fungus that lives
within grass