Predation, - PowerPoint Presentation

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.