Download How Organisms Interact in Communities

How Organisms Interact in
Communities
Ch. 18
Biology
Ms. Haut
Species Evolve in Response to
One Another

Coevolution—back & forth evolutionary
adjustments between interacting organisms
within an ecosystem

Interactions between flowers and pollinators
(birds/insects)
Amorphophallus titanum.
Collectively known as “Devil’s
Tongues,” they are botanically
in the Aroid Family (Araceae).
Devil’s Tongues have blooms
that look and smell like
something dead, which
delights and attracts the
pollinating flies.
Its tuber can grow to 6 feet in
circumference, and at
maturity will weigh 100
pounds! The eventual bloom
can measure eight feet tall
and four feet across!
Predators and Prey Coevolve

Predation—the act of feeding off another
Predators and Prey Coevolve

Parasitism—parasite lives on or in another
organism and feeds off of their “host”


Do not usually kill host –food source
Use host as nursery for offspring
Predators and Prey Coevolve


Herbivores—animals
that eat plants
Plants have defenses


Thorns, spines,
prickles
Toxins—tastes
bad or is poisonous
Predators and Prey Coevolve

Herbivores have
overcome plant
defenses

Cabbage butterfly
larvae have
enzymes that break
down mustard oils
(toxic to many
insects)

Guarantees them a
food source
Animal Defenses Against Predators

Behavioral defenses



Alarm cries
Distraction displays
Camouflage—coloration/shape


Blend in with environment
warning coloration


Red/black; yellow/black
Mechanical/chemical defenses


Quills, spines, and other similar structures
Toxins—distasteful or poisonous


Monarch butterfly stores toxin of milkweed as larvae
Poisonous toads secrete toxin
Symbiotic Relationships


Symbiosis—2 or more species live together in a
close, long-term association
Non-Beneficial


Parasitism—host harmed, not necessarily killed
Beneficial

Commensalism—one partner benefits while not
harming the other


Cattle egrets—egrets eat ectoparasites/cattle are groomed
Mutualism—both partners benefit


Lichens-association b/w fungus and algae
Nitrogen-fixing bacteria and legumes
Competition in Communities
Overproduction of offspring among species
of a community
 Limited resources in the community—
living space, food, nutrient, water, light,
mates
 Niches overlap—how an organism lives
Leads to Competition

Niche Restriction


Dividing resources
among species
Reduces competition
Prothonotary warbler—
eastern United States
Species’ Niche


Fundamental niche-entire range of
conditions an organism is potentially able
to occupy
Realized niche—the part of the
fundamental niche that a species actually
occupies
Joseph H. Connell Study
Competitive Exclusion Principle

Two species cannot coexist in a community if
their niches are identical
Community Structure
Effects of a Keystone Predator:Sea Star (Pisaster)
25
20
15
With Pisaster
Without Pisaster
10
5
68
19
69
19
70
19
71
19
72
19
67
19
66
19
65
19
64
19
63
0
19

Predators can moderate competition among its
prey species
Keystone species can alter the whole community
Number of Species
Present

Year