Community Ecology

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Character Displacement

Character displacement is a tendency for characteristics / particular traits to be more divergent in sympatric populations of two species than in allopatric populations of the same two species.

An example is variation in beak size between populations of two species of Galápagos finches.

Slide 8

Character displacement: Indirect Evidence of Past Competition

Los Hermanos

G. fuliginosa

G. fortis

Beak

depth

Daphne

G. fuliginosa,

allopatric

G. fortis,

allopatric

Sympatric

populations

Santa María, San Cristóbal

Beak depth (mm)

Percentages of individuals in each size class

60

40

20

0

60

40

20

0

60

40

20

0

8

10

12

14

16

Slide 9

Predation

Predation (+/– interaction) refers to interaction where one species, the predator, kills and eats the other, the prey.

Some feeding adaptations of predators are claws, teeth, fangs, stingers, and poison.

Prey display various defensive adaptations: such as behavior and coloration.

Slide 10

Behavioral defenses include hiding, fleeing, forming herds or schools, self-defense, and alarm calls.

Animals also have morphological and physiological defense adaptations:

Cryptic coloration = camouflage, makes prey difficult to spot.

Aposematic coloration: Animals with effective chemical defense / poison / often exhibit bright warning coloration. Predators are particularly cautious in dealing with prey that display such coloration.

Prey: Defensive Adaptations

Slide 11

Canyon tree frog

(a)

Cryptic

coloration

(b)

Aposematic

coloration

Poison dart frog

(c) Batesian mimicry: A harmless species mimics a harmful one.

Hawkmoth

larva

Green parrot snake

Yellow jacket

Cuckoo bee

Müllerian mimicry: Two “yuck”

unpalatable species mimic each other.

(d)

Slide 12

In some cases, a prey species may gain significant protection by mimicking the appearance of another species:

In Batesian mimicry, a harmless species mimics an unpalatable or harmful model… One is a “pretender.”

In Müllerian mimicry, two or more unpalatable species resemble each other… BOTH are “yuck.”

Mimicry = “Look-alikes” Defense

Slide 13

Herbivory: Herbivores = Plant Predators

Herbivory (+/– interaction) refers to an interaction in which an herbivore eats parts of a plant or alga.