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Dynamics of Ecosystems: Community Ecology
Chapter 45 Copyright © McGraw-Hill Companies Permission required for reproduction or display
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Realized Niche A organism’s niche is the total of all ways it utilizes the resources of its environment. Fundamental - Entire niche potentially available to an organism. Realized - Actual niche utilized by an organism. Habitat is the place where an organism lives.
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Realized Niche Interspecific competition - Occurs when different species attempt to utilize the same resource. Interference - Individuals fighting over the same resource. Exploitative - Individuals utilizing shared resources. Competition and Niche Use in Barnacles
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Principle of Competitive Exclusion
The Principle of competitive exclusion states that no two species utilizing the same niche can coexist indefinitely. One will eventually eliminate the other.
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Resource Partitioning
Resource Partitioning occurs when species living in the same area partition available resources to avoid direct competition. Sympatric species are similar species that live in the same geographical area. Tend to exhibit greater differences in morphology than allopatric species (species that live apart from each other). Character Displacement
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Character Displacement
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Detecting Interspecific Competition
Negative effects of one species on another do not automatically indicate competition. Presence of one species may attract a predator that consumes both, causing one species to have a lower population size than the other. Must always look at underlying ecological mechanisms.
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Predation and Prey Populations
Predation occurs when one organism consumes another. Provides strong selective pressure on prey populations. Any physiologic characteristic or behavior that would decrease the probability of capture should be strongly favored. Increased fitness Includes camouflage
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Plant Defenses Against Herbivores
Morphological Thorns, spines, etc. Chemical Secondary Chemical Compounds Evolutionary Response of Herbivores Certain groups of herbivores are associated with each group of plants protected by a particular secondary compound. Coevolution
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Animal Defenses Against Predators
Some animals that feed on plants rich in secondary compounds receive an extra benefit. Caterpillars that feed on members of the milkweed family. Copyright © McGraw-Hill Companies Permission required for reproduction or display
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Animal Defenses Against Predators
Defensive Coloration Aposematic Coloration (warning coloration) Individuals advertise poisonous nature. Cryptic Coloration Camouflage (Blending coloration) Chemical Defenses Poisons and stings Copyright © McGraw-Hill Companies Permission required for reproduction or display
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Mimicry Batesian Non-venomous snake resembles a venomous snake
Palatable insects resemble brightly colored, distasteful species. Mullerian Unrelated protected species resemble one another. Predators learn more quickly.
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Coevolution and Symbiosis
Coevolution involves long-term mutual evolutionary character adjustments of two or more species. Predator-prey interactions Symbiotic Relationships Two or more kinds of organisms live together in permanent relationships. Commensalism, Mutualism and Parasitism.
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Commensalism One species of symbiotic relationship benefits while the other is neither helped or hurt. Tropical fish and sea anemones No clear distinction between mutualism as it is difficult to determine if the second member of the relationship gains benefit. Can easily grade into parasitism.
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Mutualism Both species of relationship gain benefit.
Mutual cooperation Ants and Acacias Ant has a place to live, protects tree from harmful insects Copyright © McGraw-Hill Companies Permision required for reproduction or display
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Parasitism Bird lice on feather
Parasite is much smaller than the host and gains benefit while inflecting some form of harm to the host. Do not kill immediately. Ectoparasites External parasites - Lice Parasitoids - Lay eggs on living hosts. Endoparasites Internal parasites Extreme specialization Bird lice on feather
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Birds lay their eggs in the nests of other species. Cowbirds
Parasitism Brood Parasites Birds lay their eggs in the nests of other species. Cowbirds Copyright © McGraw-Hill Companies Permission required for reproduction or display
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Interactions Among Ecological Processes
Predation Reduces Competition Reduce numbers of competitive species. Parasitism Can Counter Competition Parasite may effect sympatric species and thus influence interspecific interactions. Keystone Species Species that have a particularly strong effect on community composition. Top predators Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies
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Interactions Among Ecological Processes
Indirect Effects Presence of one species may affect a second species through interactions with a third species. Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies
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Succession Succession is the process of ecosystems changing from a simple to a more complex structure. Primary Succession - Occurs in bare or open areas. Eutrophication of oligotrophic lakes. Secondary Succession - Occurs following a disturbance (fire, flood, etc) Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies
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Succession Climax Community - Eventual stable point of succession. Concept is now tempered by several realizations: Climate is dynamic. Succession is often slow. Region’s vegetation is determined to an extent by human activities.
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Succession Succession occurs because species alter the habitat and available resources in ways that favor other species. Key Concepts Tolerance Facilitation Inhibition
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The Role of Disturbance
Disturbances interrupt and potentially alter the succession of plant communities. Intermediate Disturbance Theory Communities experiencing moderate levels of disturbance will have greater species richness than communities experiencing either smaller or larger levels of disturbance. Simultaneous successional stages. Dominant competitors kept at bay.
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