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Chapter 21Community Ecology
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
PredationA predator captures, kills, and consumes the prey
Predation determines where and how a species lives
Regulates population size
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)
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
MimicryA harmless species resembles a poisonous one
The mimic is protected since it is avoided
Mullerian MimicryWhen several dangerous/poisonous species have similar warning coloration
Example: the black and yellow striped pattern on bees and wasps
Batesian MimicryWhen a harmless species mimics the warning coloration of a dangerous species
Example: coral snakes and scarlet king snakes
Plant-Herbivore InteractionsPlants have evolved adaptations that protect them from being eaten by herbivores
examples: thorns, spines, stinging hairs, tough leaves, chemical defenses
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!
ParasitismOne individual is harmed while the other benefitsThe parasite feeds on the hostEctoparasites (external)Endoparasites (internal)
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)
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
Competition in ParameciaG.F. Gause studied competition between two species of paramecia in the lab
Character DisplacementCompetitors may evolve niche differences or anatomical differences that lessen the competition
Example: Darwins finches
Resource PartitioningWhen similar species coexist, each species uses only part of the available resources
Example: warblers forage in different types of trees
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)
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
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
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
Tropical RainforestsClimate is more stable than a temperate area Plants can photosynthesize year-roundTropical rainforests have the highest biodiversity on Earth
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
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
21.3 SuccessionA gradual process of change and replacement of the types of species in a community
Ecosystems are constantly changing
Primary SuccessionOccurs on a surface where no ecosystem existed before
Example: rocks, volcanic islands, cliffs, sand dunes
Primary SuccessionHappens very slowly
Bare rock lichens moss grasses shrubs trees
Example: Galapagos Islands
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
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
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
Old-field Succession