Ch. 5, Sec 2: Interactions in Communities p109-111

Section 2: Interactions In Communities

• How do predator-prey interactions influence both predators and prey?

• How are plants protected from herbivores?

• How does symbiosis work?

• What are examples of all these relationship?

Ch. 5, Sec 2: Interactions in Communities p109-111

Vocabulary List

• Predation (predator, prey)• Herbivory• Symbiosis• Parasitism (parasite, host)• Mutualism• Commensalism

Ch. 5, Sec 2: Interactions in Communities p109-111

1) Predator-Prey Interactions

• Predation is one organism killing another for food (prey dies).

• The predator is usually bigger or more powerful than the prey

• The prey population is larger than the predator population

• The predator population usually follows the prey

Ch. 5, Sec 2: Interactions in Communities p109-111

Predator-Prey Interactions, cont.

See Visual Concept 60350: PREDATION

Ch. 5, Sec 2: Interactions in Communities p109-111

2) Herbivory

• Herbivores are animals that eat plants.

• Unlike predators, herbivores do not often kill the plants.

• Plants might defend themselves with thorns, tough leaves, or bad tasting or toxic chemicals.

• See Visual Concept 60352: HERBIVORY

Ch. 5, Sec 2: Interactions in Communities p109-111

3) Other Interactions: Symbiosis

• Not all interactions between organisms result in a winner and a loser.

• Symbiosis is a relationship in which two species live in close association with each other.

• One species benefits, and the other might or might not.

• Three types of symbiosis:

1) Parasitism2) Mutualism 3) Commensalism

Ch. 5, Sec 2: Interactions in Communities p109-111

Parasitism

• In parasitism, a parasite feeds on another organism called a host.

• The host is almost always larger than the parasite, and is usually harmed but not intentionally killed.

• Parasites often live on or in their host. Therefore, the parasite depends on its host not only for food but for a place to live as well.

• Examples: fleas, tapeworms, mosquitoes, ticks, leeches

Ch. 5, Sec 2: Interactions in Communities p109-111

Parasites, continued

• Hosts try to keep parasites from infecting them. Hosts can defend themselves with their immune systems or behaviors such as scratching.

• Are humans “furless” to avoid parasites?

• In response, parasites may evolve ways to overcome the host’s defenses (immunity to drugs, for example)

• See “Protists and Humans” (p.507-509) for more on parasites and disease.

Ch. 5, Sec 2: Interactions in Communities p109-111

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Ch. 5, Sec 2: Interactions in Communities p109-111

Mutualism

• A relationship between two species in which both species benefit.

– Cleaner fish & larger fish – Bees & flowers– Fungi + Algae = Lichen

Ch. 5, Sec 2: Interactions in Communities p109-111

Commensalism

• One species is helped, but the other is neutral.

• Orchids, vines growing on forest trees to reach sunlight

• Sea anenome & clown fish• Bacteria in animal intestines (?)

Ch. 5, Sec 2: Interactions in Communities p109-111

Summary1. Predators kill prey for food; populations are related

2. Herbivores eat plants, but plants can defend through thorns, bad taste, or toxins

3. Symbiosis is close connection between two species; at least one benefits

Relationship Species A Species BParasitism Helps HurtsMutualism Helps HelpsCommensalism Helps Neutral

Ch. 5, Sec 2: Interactions in Communities p109-111

Knowledge Check

1. Explain how an animal could be both predator and prey.

2. How are herbivores different from carnivorous predators?

3. How is parasitism different from predation?

4. There are more bacteria cells in the human body than there are human cells! What type of relationship is this?