Community EcologyCommunity Ecology

Relationships Between OrganismsRelationships Between Organisms

AP Biology

Ecological Niches

• A species' niche includes:

• Habitat - where it lives in the ecosystem

• Relationships - all interactions with other species in the ecosystem

• Nutrition - its method of obtaining food

Competition

• Competition = when two species compete for the same resource

• Competition can lead to competitive exclusion or resource partitioning

Competitive Exclusion

• Competitive Exclusion Theory– 2 species cannot occupy the

same niche– If 2 species occupy the same

niche, then they will compete until one eliminates the other (becomes extinct)

Resource Partitioning

• If one species’ niche is modified through natural selection, then it will be able to coexist with the other species (that it competed with before).– niche differentiation

– Modified use of resources

Character Displacement

• Is evidence of previous competition between species

• Allopatric Speciation = speciation that occurs in species that are geographically isolated from each other

• Sympatric Speciation = speciation that occurs in species that live in the same area

Character displacement

• How does the diagram show evidence of competition?

• When the populations live together, character displacement occurs in order for the populations to co-exist (sympatric speciation)

Animal Defenses: Aposematic coloring

Coloring or markings to warn off predators

Animal Defenses : Cryptic coloration

Coloring that disguises an animal’s shape

Animal Defenses: Batesian MimicryA species mimics a successful species but lacks the actual attribute– “pretending to be harmful”

Scarlet king snake

harmful

Not harmful

Müllerian Mimicry

Monarch butterfly

Viceroy butterfly

A species resembles another successful (harmful) species and shares the attribute (is also harmful)

Plant Defenses Against Herbivory

• Thorns and spines

• Glandular hairs– store and secrete toxins

• Deposition of crystals in plant tissues– makes tissues tougher

• Chemical compounds– May be distasteful or toxic to animals– May cause abnormal development in animals

Images taken without permission fron http://www.ext.vt.edu/news/periodicals/cses/1998-02/Glandular_hair_leaf_72dpi.JPG and http://fm2.fieldmuseum.org/plantguides/jpgs/LOGA-stry-toxi-pan-2735.jpg

Summary of Species-Species Interactions

Competition -/-

Predation +/-

Herbivory +/-

Parasitism +/-

Disease (Pathogen) +/-

Mutualism +/+

Commensalism +/0

Keystone Species

• species that has a strong influence on its ecosystem. – Ex. Sea otters, prairie dogs

• If it is not there will cause populations of other species in the ecosystem to go down or become extinct;

• Can drastically change the ecosystem even though it isn’t the most abundant species. – Dominant species = most abundant species

Images taken without permission from http://animal.discovery.com/mammals/prairie-dog/ and http://carinbondar.com/2010/11/this-weeks-cool-biology-job-sea-otter-population-ecologist/