Chapter 21 Community Ecology. 21.1 Species Interactions Communities contain populations that...
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Transcript of Chapter 21 Community Ecology. 21.1 Species Interactions Communities contain populations that...
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Chapter 21Community Ecology
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21.1 Species InteractionsCommunities contain populations that interact in many ways
There are five major types of interactions (symbioses): predation, parasitism, competition, mutualism, and commensalism
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PredationA predator captures, kills, and consumes the prey
Predation determines where and how a species lives
Regulates population size
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Predators and Natural SelectionNatural selection favors adaptations that improve the efficiency of predators (the better the hunter, the more food to survive)
Examples: predator adaptations such as coat color, sharp teeth or claws, able to find prey (sense of smell, accurate vision)
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Prey and Natural SelectionThe survival of prey animals depend on their ability to avoid being eaten
Examples: camouflage, poison, behavior, ability to hide, able to outrun predator
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MimicryA harmless species resembles a poisonous one
The mimic is protected since it is avoided
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Mullerian MimicryWhen several dangerous/poisonous species have similar warning coloration
Example: the black and yellow striped pattern on bees and wasps
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Batesian MimicryWhen a harmless species mimics the warning coloration of a dangerous species
Example: coral snakes and scarlet king snakes
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Plant-Herbivore InteractionsPlants have evolved adaptations that protect them from being eaten by herbivores
examples: thorns, spines, stinging hairs, tough leaves, chemical defenses
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Secondary CompoundsSome chemicals in plants are poisonous, irritating, or bad-tasting
Many plant chemicals are used for medicines
There are many medicinal cures in rainforest plants, but they are being destroyed due to habitat destruction!
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ParasitismOne individual is harmed while the other benefitsThe parasite feeds on the hostEctoparasites (external)Endoparasites (internal)
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Parasitism and EvolutionParasitism has caused an evolution of a variety of host defenses
Natural selection favors adaptations that allow a parasite to exploit its host (very specialized bodies and lifestyles)
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CompetitionThe use of the same limited resource by two or more species
Competitive exclusion: one species can be eliminated from a community because of competition
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Competition in ParameciaG.F. Gause studied competition between two species of paramecia in the lab
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Character DisplacementCompetitors may evolve niche differences or anatomical differences that lessen the competition
Example: Darwins finches
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Resource PartitioningWhen similar species coexist, each species uses only part of the available resources
Example: warblers forage in different types of trees
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MutualismA cooperative relationship in which both species benefit
example: pollination (pollinators are attracted to a food source and transfer pollen to other flowers while feeding)
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CommensalismOne species benefits while the other is not affected
Example: cattle egrets feed on insects that fly out of the grass when the Cape buffalo is walking
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21.2 Properties of CommunitiesSpecies richness: the number of species a community contains
Species diversity: relates the number of species to the relative abundance of each species
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Patterns of Species RichnessVaries with latitudeThe closer to the equator, the more species (greatest in tropical rainforests)E.O. Wilson found more ant species in a single tree in Peru than there are in the entire British Isles
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Tropical RainforestsClimate is more stable than a temperate area Plants can photosynthesize year-roundTropical rainforests have the highest biodiversity on Earth
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The Species-Area EffectLarger areas usually contain more species than smaller areas (more habitats)
Most often applied to islands
Reducing the size of a habitat reduces the number of species
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Community StabilityStability refers to a communitys resistance to change and is directly related to species richness
The more species, the more interactions and the better a habitat can withstand a disturbance
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21.3 SuccessionA gradual process of change and replacement of the types of species in a community
Ecosystems are constantly changing
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Primary SuccessionOccurs on a surface where no ecosystem existed before
Example: rocks, volcanic islands, cliffs, sand dunes
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Primary SuccessionHappens very slowly
Bare rock lichens moss grasses shrubs trees
Example: Galapagos Islands
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Secondary SuccessionMost common type of succession
Occurs on a surface where an ecosystem previously existed
Occurs after an ecosystem is disturbed by humans or by storms, floods, earthquakes, or volcanoes
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Secondary SuccessionPioneer species- the first organisms to colonize any newly available area
Grasses and weeds shrubs shade intolerant trees shade tolerant trees climax community
Example: eruption of Mt. St. Helens destroyed 44,460 acres of forest
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Old-field SuccessionWhen farmland is abandoned, it will start to turn back into a forest ecosystem
Pioneer plants such as grasses and weeds will start to grow
After about 100 years, the field will return to a climax community
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Old-field Succession