Community Ecology

No organism lives alone. Each organisms affects and is affected by other species and its environment. 1

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Species InteractionsJust as populations contain interacting members of a single species, communities contain interacting populations of many species.

There are five major types of interactions, or symbiotic relationships among species:

• Predation (+/-)• Parasitism (+/-)• Competition (-/-)• Mutualism (+/+)• Commensalism (+/o)

A symbiotic relationships is one in which different species live in close association with one another.

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The organism that kills and eats the prey is called the predator.

Predators are an important part of an ecosystem.

Predators often kill the weak members of a population. They keep the population size of prey animals in balance.

Organisms depend on each other for survival. Many organisms feed on other organisms. The organism that is eaten is called the prey.

Predation

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For Example:The Mouse is considered the predator when it preys on plants

The snake is the predator when it preys on the mouse, which is then the prey.

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Parasitism

FYI ~ Ticks, for example, can be parasites of dogs. The dog is the host. Ticks feed on the blood of the dog and may pass diseases to the dog. Although parasites harm their host, they usually do not kill them. This is because the parasite depends on the host for survival.

Parasitism is one kind of symbiotic relationship.

A parasitic relationship is one in which one organism is helped and the other is harmed. The organism that a parasite lives on is called the host.

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FYI ~ Parasitism

In a bizarre parasitic death sentence, a fungus turns carpenter ants into the walking dead and gets them to die in a spot that's perfect for the fungus to grow and reproduce.

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CompetitionCompetition results from niche overlap – two or more species competing for the same resource(s). One can be negatively impacted by the presence of the other because they will have less food or space.

Sea Anemones are constantly

engaged in competition for territory.

Cheetahs and lions can also be in competition, since both species feed on the same prey.

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CommensalismCommensalism is a relationship in which oneorganism benefits and the other organism is not harmed but does not benefit either. Example: cattle egrets eat lizards forced out of hiding by buffalo’s movements.

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FYI ~ Commensalism

Spanish moss often grows on the limbs of trees. The moss benefits from the

tree by having a place to live. The tree does not benefit from the moss, but it is not harmed by the moss, either.

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FYI ~ CommensalismBarnacles adhering to the skin of a whale is an example of commensalism. For a hungry barnacle, the rim of a whale’s nostril isn’t a terrible place to be. When the whale swims through a cloud of plankton for a meal, the barnacle which also feeds on the tiny, floating organisms, too, gets free table service.

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MutualismMutualism is a relationship that helps both organisms.Example:

-Pollinators and plants have one of the most important mutualistic

relationships.

Pollinators-animals that carry pollen.

Plants try to attract pollinators by using flowers.

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FYI ~ Mutualism

The ants defend the tree from being eaten. At the same time, the ants feed on milky sap produced by the tree…The tree gets protection, the ant gets food !!

An acacia tree has thorns on its branches. However, there are some animals, such as giraffe, that can eat around the thorns. When this happens, ants that live on the acacia tree attack the animal.

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FYI ~ MutualismThe great barracuda spends much of its life just floating in the water, but during this time it is taking part in a mutualistic relationship with a little fish known as the cleaner wrasse. The barracuda sits in the water with its mouth partly open and its gills flared to allow the wrasse to eat off dead skin and parasites. This relationship could even be considered obligate mutualism because without the wrasse, the barracuda's gills would be clogged with dead skin and without the barracuda, the wrasse would have no source of food.

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Check Your Understanding

4. What does symbiosis mean?5. CRITICAL THINKING:

A bumble bee helps pollinate flowering plants while getting nectar from the flower. What type of relationship does this represent?

Answer the questions in complete sentences:

1. What is an ecosystem?2. What is a community?3. What is a niche?

Properties of Communities The ability of a community to bounce back

after major disturbances depends on several properties of the community:– the interactions of species within the

community (predator-prey relationships)– the number of species (richness) the

community contains– the kind of species the community

contains (diversity)– The stability of the community (its

resistance to change)

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Succession

The populations of an ecosystem can change quite a bit over a long period of time.

The gradual, sequential re-growth of species in an area is called succession.

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Normally in succession, the plants are the populations that re-grow first. Then, animal populations will return to the community.This rotting log is an example of an ecosystem undergoing succession.

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Two Types of SuccessionPrimary Succession: life begins to grow in an area where there was previously no life and no soil.Ex: bare rock, a sand dune, volcanic eruption, glacier

Secondary Succession: life repopulates an area that has been destroyed, but the soil has remained.Ex: forest fire, flood, devastating human activityhttp://www.quia.com/jfc/2524430.html?AP_rand=502495504

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SuccessionAny possible area that has the potential to be a new habitat is an invitation to many species to set up residence.These hardy species that are the first begin a new community are called pioneer species (i.e. crabgrass, ragweed, algae, moss, lichen)

Succession

19It can take more than 100 years for an ecosystem to go through all of the stages of succession.

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Succession

TAKE THIS QUIZ

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Succession

Succession continues until it has reached a stable new community. This community is referred to as a climax community.

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FYI ~Humans Can Change EcosystemsHumans have an effect on the ecosystems they livein. For example, for many years, people in the western US feared wolves. Gray wolves were hunted and killed until there were few left. People did not realize that the wolves were an important part of the ecosystem.

The wolves kept the populations of other

animals in balance by feeding on herbivores such as deer & rabbits. By reducing the number of wolves, humans changed the balance in the ecosystem.