COMMUNITY INTERACTIONS

Ecology Unit

Notes due: September 4, 2015

Competition• When organisms attempt to use the same limited

ecological resource in the same place at the same time, competition occurs.

• Types of Competition• Intraspecific: between members of the same species.• Interspecific: between members of different species.

Example: Plant roots compete for water and nutrients in the soil.

Example: Animals compete for food, mates, and place to live and raise their young.

The Competitive Exclusion Principle

• Direct competition between species almost always produces a winner and a loser- and the losing species dies out.

• Example: Two species of paramecium• When grown in identical, but separate cultures, both

species survived.• When grown in same culture, one species out

competed the other.

• The competitive exclusion principle states that no two species can occupy exactly the same niche in exactly the same habitat at exactly the same time.• The species that is better at competing for limited

resources will thrive.

When grown together, one species dies out.

Dividing Resources

• Competition creates pressure for each species to specialize the way that it uses resources, in order to survive and reproduce.

• By causing species to divide resources, competition helps determine the number and kinds of species in a community and the niche each species occupies.

Example: North American warblers• Three species of warblers live in the same tree and

eat insects.• One species feeds on high branches, another feeds on

low branches, and another feeds in the middle.• Each species has its own niche, which was probably

established due to past competition.

Predation and HerbivoryPredator-Prey Relationships• The interaction in which a predator feeds on prey is called

predation.• Predators can affect the size of prey populations in a

community and determine the places prey can live and feed.

• Example: birds of prey play an important role in regulating population sizes of mice and voles.

Herbivore-Plant Relationships• The interaction in which an herbivore feeds on produces is called

herbivory.• Herbivores affect both the size and distribution of plant

populations in a community and determine the places that certain plants can survive and grow.

• Example: White-tailed deer are eliminating some plant species across the United States.

Keystone Species• Sometimes the effect of a single species on

community structure is so important that changes in its population can impact the structure and stability of an ecosystem.

• Example: Sea otters• Food chain: algae kelp sea urchins sea

otters• Otters with nearly eliminated by hunting.• Sea urchin population skyrocketed, which

caused the kelp population to nearly disappear.• Sea otters were vital to the success of the

ecosystem.

• A keystone species is a single species that is vital to ecosystem stability.

Symbioses• A particularly close, interdependent relationship between two species is called symbiosis.

•Mutualism• Definition: a relationship

between two species in which both benefit.• Example: Clownfish and

anemones

• When clownfish are threatened, they seek shelter in the anemones (the tentacles can kill or paralyze other fish).

• If an anemone-eating species tries to attack of eat the anemone, the clownfish chase them away.

Parasitism• Definition: a relationship in which one organism

lives inside or on another organism.• Parasite obtains all or part of its nutritional needs

from the host.• Parasites weaken but do not kill their host.• Example: Fleas, tick, lice, and leeches live on the

bodies of mammals, feeding on their blood and skin.

Commensalism• Definition: a relationship in which one

organism benefits and the other is neither helped nor harmed.

• Example: Barnacles attach to the skin of grey whales, so they can feed on food in the water that passes over the whale. The what is not positively or negatively affected.