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Chapter 17: Predation and
Herbivory
Consumer-Resource Interactions
• All life are both:
– consumers (C) of victims  Predators
– victims (V) of consumers  Prey
• Interactions organize communities into consumer
chains (food chains):
– consumers benefit at the expense of their resources
– populations are controlled from below by resources and
from above by consumers
Opuntia
(Prickly pear)
Cactoblastis
(cactus moth)
Before Cactoblastis introduction
Queensland Australia ~1950’s
After Cactoblastis introduction
Some Definitions
• Predator
– catches and consumes individual prey items
– thereby removing them from the prey population (V).
• Parasites
– consume parts of a living prey organism, or host
– parasites may be external or internal
– may negatively affect the host but does not directly
remove it from the population
Predator
More Definitions…
• Parasitoids
– consumes living tissues of their hosts, eventually killing
them
– combination parasite and predator
• Herbivores
– eat whole plants or parts of plants
– may act as predators (eating whole plants) or as
parasites (eating parts of plants):
• grazers eat grasses and herbaceous vegetation
• browsers eat woody vegetation
Parasitoid Wasp
A detritivore’s niche…
• Detritivores
– consume dead organic material.
– consume wastes of other species.
– have no direct affect on populations that produce these
resources:
• do not directly affect prey abundance
• do not directly influence their evolution
– are important in the recycling of nutrients within
ecosystems
Predator adaptations.
• Predators vary in size relative to their prey:
– predators may be much larger than their prey (whales are
far larger than krill and small fish)
– prey are rarely much larger than their predators:
• beyond a certain prey size, a predator cannot successfully subdue
and consume the prey
• cooperative hunters are an exception, taking prey substantially
larger than themselves
– form usually tied to specific diet (vertebrate teeth example)
Carnivore consuming small
prey items to satisfy requirements
(cost increases exponentially as predator size inc.)
General adaptations?
Predator adaptations (cont.)
• The variety of predator adaptations is
remarkable:
– consider grasping and tearing functions:
• forelegs for many vertebrates
• feet and hooked bills in birds
• distensible jaws in snakes
– digestive systems also reflect diet:
• plant eaters feature elongated digestive tracts with
fermentation chambers to digest long, fibrous
molecules comprising plant structural elements
Osprey feet
Prey adaptations.
• Prey escape mechanisms:
– in animals:
– in plants:
• Bombardier beetle
Crypsis and Warning Coloration
• Crypsis - blending with background:
–
–
–
–
are typically palatable or edible
match color, texture of bark, twigs, or leaves
not concealed  mistaken for inedible objects
behaviors corresponds to appearances.
Crypsis
Peruvian katydid
• Costa Rican
mantid
Lonomia moth in Costa Rica
Scorpion fish in Philippines
• Sage thrasher
• American Dipper
Jack-snipe
Warning Coloration
• Unpalatable animals
– Noxious chemicals
• From food
• Manufacture
Why aren’t all prey unpalatable?
– Often warning is involved
• predators learn to avoid such animals after unpleasant
experiences
• certain aposematic colorations occur so widely that predators
may have evolved innate aversions
Mimics
• Henry Bates – palatable species mimic
unpalatable (models)
• Fritz Müller –unpalatable species that come
to resemble one another (all mimics and
models)
Batesian mimics
Müllerian mimics
Parasites adaptation = dispersal
• Parasites usually smaller than host
• Externally (ectoparasite) or internally
– internal parasites exist in a benign environment:
• food
• stable conditions
Internal parasite
Tapeworm of US soldier in Hawaii.
Left: after barium infusion. Right: after
vermifuge treatment
Ectoparasites
Purple finch
Cost of being a parasite…
– parasites must deal with a number of
challenges:
• host organisms have mechanisms to detect and
destroy parasites
• parasites must disperse through hostile
environments,
• often via complicated life cycles with multiple hosts,
Plasmodium life cycle
Fusion of gametes
Feeding
mosquito ingests
gametes
Zygote forms cyst
in gut wall of
mosquito
Zygote divides
into sporozoites
Some merozoites
form into male
and female
gametes
Salivary
glands
48-hr cycle
of invasion,
lysing,
reinvasion
Merozoites can:
1) Reinfect liver cells
2) Infect rbc’s
Liver cells
Injection of
sporozoites
into human
host’s blood
One strategy…
• Circumventing the host’s immune system:
– suppress it (AIDS virus)
– coat themselves with proteins mimicing host’s
proteins (Schistosoma)
– continually coat their surfaces with novel
proteins (trypanosomes)
Plants vs. herbivory
• Usually biochemical warfare.
• Plant defenses include:
“Secondary” Compounds
– low nutritional content
– toxic compounds
– structural defenses
• spines and hairs
• tough seed coats
• sticky gums and resins
constitutive
induced
Can herbivores overcome plant’s
defenses?
Can herbivores control plant
populations?
– prickly pear cactus in Australia
• controlled by introduction of a moth, Cactoblastis
– Klamath weed in western US
• Controlled by Chrysolina beetles
Other examples…
• Mauna Loa, Hawaii
grazed
Spruce budworm – Algonquin PP in
Ontario, Canada