Download Ch 8 Negative species interactions*infection and parasitism

Ch 8 Negative species interactions—
infection and parasitism
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Pathogens and parasites have negative impacts on species
Compartment models are useful for analyzing how diseases affect populations
– Parameters of compartment models
– epidemics
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Pathogens and parasites affect individual organisms by reducing reproductive
output and increasing mortality
– Effects on reproduction
– Effects on mortality
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Diseases can reduce populations
– Brucellosis in ungulates
– Rabies in wild mammals
– Myxomatosis in the European rabbit
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Pathogens can become more or less virulent through evolution, and their hosts
can evolve resistance
– Evolution of virulence
– Coevolution in disease systems
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Parasites Among Us
• Symbionts are organisms that live in or on
other organisms.
– A parasite consumes the tissues or body fluids
of the organism on which it lives, its host.
– Pathogens are parasites that cause diseases.
• More than half of the millions of species
that live on Earth are symbionts.
Figure 13.3 The Human Body as Habitat
Parasite Basics
Concept 13.1: Parasites, which constitute
roughly 50% of the species on Earth, typically
feed on only one or a few host species.
• Size
– Macroparasites are large, such as arthropods
and worms.
– Microparasites are microscopic, such as
bacteria.
• Location
– Ectoparasites live on the outer body surface of the
host.
– Endoparasites live within the host, in the alimentary
canal, or within cells or tissues
Figure 13.4 Many Species Are Host to More Than One Parasite Species
Announcements
• Papers due Monday in class
• Homework due Monday
• Dropping lowest homework grade
Defense and Counterdefense
Concept 13.2: Hosts have adaptations for
defending themselves against parasites, and
parasites have adaptations for overcoming
host defenses.
• Host organisms have many kinds of defense
mechanisms.
• Protective outer coverings include skin and
exoskeletons. Many parasites that do gain
entry are killed by the host’s immune
system.
Figure 13.8 Using Plants to Fight Parasites
Coevolution
Concept 13.3: Host and parasite populations
can evolve together, each in response to
selection imposed by the other.
• When a parasite and its host each possess
specific adaptations, it suggests that the
strong selection pressure hosts and
parasites impose on each other has caused
both of their populations to evolve.
Figure 13.10 Coevolution of the European Rabbit and the Myxoma Virus (Part 1)
Figure 13.10 Coevolution of the European Rabbit and the Myxoma Virus (Part 2)
Figure 13.11 Adaptation by Parasites to Local Host Populations
Ecological Effects of Parasites
Concept 13.4: Parasites can reduce the sizes
of host populations and alter the outcomes of
species interactions, thereby causing
communities to change.
• Reduce survival or reproduction of host
• Alter species interactions
• Alter population cycles
Figure 13.14 Parasites Can Reduce Host Reproduction (Part 1)
Figure 13.14 Parasites Can Reduce Host Reproduction (Part 2)
Figure 13.15 Parasites Can Reduce Their Host’s Geographic Range
Figure 13.17 Parasites Can Alter the Outcome of Competition
Figure 13.16 Parasite Removal Reduces Host Population Fluctuations
Applications: Disease and Pest Control
Concept 13.5: Simple models of host–
pathogen dynamics suggest ways to control
the establishment and spread of diseases.
dI
 SI  dI
dt
Containing Disease
• Key is keeping the number of susceptible
individuals below the threshold.
• Susceptible domestic animals are
sometimes slaughtered to reduce density,
especially if the disease can also affect
humans, such as bird flu.
• Quarantines may also be imposed
Figure 13.19 Vaccination Reduces the Incidence of Disease
Figure 13.20 Determining Threshold Population Densities
Other Types of Parasites
• Nest parasites
• Parasitoids