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 Predators can moderate competition among its

prey species Keystone species can alter the whole community

Effects of a Keystone Predator:Sea Star (Pisaster)

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