Transcript Predation, Herbivory, and Parasitism

Predation,
Herbivory, and
Parasitism
Types of Species Interactions
 When
two species interact, the effects for
each species can be positive, negative,
or neutral.





Competition -/Amensalism -/0
Commensalism +/0
Mutualism +/+
Exploitation +/-
Types of Species Interactions
 Exploitative
include:



Predation
Herbivory
Parasitism
interactions
Parasitism



Parasites live in or on their host's body and
often spend most or all their lives eating tissues
or body fluids of just one host individual.
Sometimes multiple generations of parasites
live on the same host.
Because parasites depend on their hosts for
continued feeding, they do not generally kill
their hosts (at least not immediately).
Parasitism


Most parasites
associated with a single
host species have a
free-living life stage
during which they are
not attached to a host.
A great many other
parasites, though, have
multiple hosts with
different life stages
adapted to each host
(and possibly free-living
stages as well).
Endoparasites

The inside of an
organism is a much
more stable and
protected
environment than the
outside,
and endoparasites (e
ndo = inner) take
advantage of this by
living and feeding
inside their hosts
Ectoparasites
 Although
parasites
tend to be tiny and
hard to
see, ectoparasites
(ecto=outer), which
live on the outside
surface of their host,
are often easier to
observe.
Ectoparasites
 By
living outside their host, ectoparasites
avoid having to defend themselves
against the host's immune system.
 The trade-off, however, is that they are
exposed to predation and a sometimes
harsh exterior environment.
 Some species of predators specialize on
ectoparasites.
Ectoparasites
 The
cleaner
wrasse is a type of
fish that lives in
coral reefs.
 Other fish will wait
patiently while a
cleaner fish picks
off parasites from
their scales,
mouth, and gills.
Parasitoids and Hyperparasites



Most of the parasites discussed so far do not
directly kill their hosts but, parasitoids do.
Parasitoids develop inside their host and essentially
eat it from the inside out.
When the host is completely consumed, the
parasitoid transforms into an adult and crawls out
to find new hosts for its offspring.
Parasitoids and Hyperparasites
 Interestingly,
the parasitoid wasp has a
parasitoid of its own, known as a
secondary parasitoid, or hyperparasitoid.
 Hyperparasitoid wasps find aphids with
internal parasitoid larvae and lay eggs
inside the larvae.
Ecological Impacts of
Parasites


Parasites can have broad
ecological impacts.
These effects begin at the
individual level; because
parasites rob their hosts of
resources, host survival
and/or reproduction can
be reduced even when
hosts are not killed by
parasites directly.
Effects of Parasites on
Individual Hosts




A protozoan causes rats to
become attracted to cats.
A nematode turns the bellies
of Amazonian ants red,
attracting berry-eating birds.
A fluke makes ants climb grass
stems so they will be eaten by
sheep.
A trematode causes killifish to
swim closer to the surface of
the water, making them easy
targets for birds.
Herbivores


Grazers are herbivores
that specialize on
herbaceous plants
(grasses, forbs, and herbs),
while browsers eat the
leaves, bark, and twigs of
woody plants.
Herbivores that specialize
on seeds are granivores,
while those specializing on
fruits are frugivores.
Plant Defenses Against
Herbivory
 Herbivory
is generally not a positive
experience for a plant, so plants have
evolved forms of self-defense.




Mechanical - Developing structures like thorns
that make it harder for animals to eat them.
Chemical - Producing chemicals that are
noxious or poisonous to herbivores.
Nutritional - Growing structures that are less
nutritious for grazers (have less N and P).
Tolerance - Adaptions to regrow quickly after
being grazed.
Impacts of Herbivory on Plant
Communities
 Herbivory
can
reduce the overall
number of plants
and can also
have a profound
impact on the
composition of a
plant community.
Impacts of Herbivory on Plant
Communities
 When
plants have evolved without
selective pressure from herbivory, they
may not be very well-defended, and the
influence of herbivores can be even more
drastic.

This is a problem when new herbivores are
introduced.
Predation
 Lynx
are fast, but lack
endurance, so they
don't chase hares
over long distances.
 Instead,
they stalk hares,
hiding behind trees
and brush until they
can get close enough
to pounce on a hare.
Predation
 Stalking
is one of a variety of strategies
used by predators for catching mobile
prey.
 Others include pursuit, where the
predator chases prey over a
distance; ambush, where the predator
hides and waits in one spot until prey
comes along; and random encounter,
where the predator and prey meet by
chance.
Animal Defenses Against
Predation
 Just
as plants have evolved defense
mechanisms to combat herbivory,
animals have evolved ways to defend
themselves from predation.



Chemical - Producing chemicals that are
noxious or poisonous to predators.
Physical - Developing physical barriers to
predation (e.g., shells).
Behavioral - Behaving in ways that minimize
risk from predation.
Animal Defenses Against
Predation



Aposematism - Warning
colors, sounds, or other
characteristics to alert
predators that this prey will
not be tasty.
Crypsis - Camouflaged
colors, shapes, and other
ways of hiding from
predators.
Mimicry - Looking, sounding,
or in other ways mimicking a
species that predators
avoid.
Predator-Prey Dynamics

Lynx & Snowshoe hare
population size records
available back to 1800s.



Fur traders
Populations of lynx and
hare seemed to follow an
interesting cyclic pattern.
Both species peak and
then sharply decline about
every ten years, at slightly
non-overlapping intervals.
Prey Dynamics: Modeling Hare
 Scientists
often use computer models to
investigate how different underlying
mechanisms might produce particular
dynamics in systems.
Cycling and Extinction


As the prey population size drops from predation, the
predators have less and less food to eat, causing the
predator population size to drop.
With fewer predators, the prey population starts
growing again, and the cycle repeats.
Interactions among Trophic
Levels
 Predators
do not act
alone in determining
whether prey
populations can survive.
 Prey can also be strongly
affected by the
availability and quality
of their food.
Deterministic vs. Stochastic
 The
deterministic Lotka-Volterra predatorprey model predicts regular, even cycles
of predator and prey populations, with
predator cycles following prey cycles.
 More realistic models that include chance
(stochastic) events show variation in both
the period and amplitude of predatorprey cycles.