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 ID: 552710
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Slide1
Predation, Herbivory, and ParasitismSlide2
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 +/-Slide3
Types of Species Interactions
Exploitative interactions include:
Predation
Herbivory
ParasitismSlide4
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). Slide5
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).Slide6
Endoparasites
The inside of an organism is a much more stable and protected environment than the outside, and
endoparasites
(
endo
= inner) take advantage of this by living and feeding inside their hostsSlide7
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. Slide8
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
.Slide9
Ectoparasites
T
he
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. Slide10
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. Slide11
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. Slide12
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.Slide13
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.
Slide14
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
.Slide15
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.Slide16
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. Slide17
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.Slide18
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. Slide19
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.Slide20
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.Slide21
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
.Slide22
Predator-Prey Dynamics
Lynx & Snowshoe hare population size records available back to 1800s.
Fur traders
P
opulations
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.Slide23
Prey Dynamics: Modeling Hare
Scientists often use computer models to investigate how different underlying mechanisms might produce particular dynamics in systems.Slide24
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.Slide25
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. Slide26
Deterministic vs. Stochastic
The
deterministic
Lotka-Volterra
predator-prey 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 predator-prey cycles.