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Ecological community
- Ecological community: all the interacting populations within an ecosystem
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biotic
- biotic, or living, portion of an ecosystem
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Interactions between populations in a community help limit their size
- Populations maintain a balance between resources and the numbers of individuals consuming them
- The process by which two interacting species act as agents of natural selection on one another is called coevolution
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Community Interactions
- Interspecific (survival & reproduction)
- Competition, which harms both species (-/-)
- Predation, which benefits the predator but harms the prey ( +/-)
- Herbivory (+/-)
- Symbiosis:
- Parasitism (+/-)
- Mutualism (+/+)
- Commensalism (+/0)
- Facilitation, not necessarily intimate contact (+/+, 0/+)
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Symbiosis
- Parasitism (+/-)
- Mutualism (+/+)
- Commensalism (+/0)
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Ecological Niche and Competition
- Each species occupies a unique ecological niche
- Its physical home or habitat
- The physical and chemical environmental factors necessary for its survival
- nesting sites, climate, and the type of nutrients it needs
- The role that the species performs within an ecosystem
- no two species ever occupy exactly the same ecological niche within a community
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competitive exclusion principle
- The competitive exclusion principle states that if two species occupy exactly the same niche with limited resources, one will outcompete the other
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resource partitioning
- resource partitioning: “ghost of competition past” (coevolution)
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North American warbler (5 species) - all hunt for insects and nest in the same type of eastern spruce tree
- each species concentrates its search for food in specific regions within spruce trees, employs different hunting tactics, and nests at a slightly different time
- the warblers minimize the overlap of their niches and reduce interspecific competition
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Resource Partitioning
Different types of warblers eat different parts of the tree
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Interspecific Competition- barnacles
- Interspecific competition may reduce the population size and distribution of each species
- Chtlamalus and Balanus barnacles
- Chthamalus occupies the upper shore
- Balanus occurs in the lower shore
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Intraspecific competition
- Competition within a species is a major factor controlling population size
- Intraspecific competition: the most intense form of competition
- major factor controlling population size
- The evolutionary result is….(you know this!)
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herbivores
- herbivores (animals that eat plants)
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predators
- Predators eat other organisms; these include herbivores (animals that eat plants)
- carnivores (animals that eat other animals)
- tend to be less abundant than their prey
- pursue: fast, agile
- lie and wait (ambush): disguised
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prey
- Prey behavior: hiding, fleeing, forming schools/herds, alarm calls
- defensive adaptation: cryptic coloration, warning coloration, mimicry
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warning coloration
- Bright colors often warn of danger
- Some animals have evolved bright warning coloration that attracts the attention of potential predators
- Warning coloration advertises that the animal is bad-tasting or poisonous before the predator attacks
- Examples include poison arrow frogs, coral snakes, and honey bees
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Mimicry
- Mimicry: members of one species have evolved to resemble another species
- Two or more distasteful species may each benefit from a shared warning coloration pattern (Müllerian mimicry)
- Predators need only experience one distasteful species to learn to avoid all with that color pattern
- For example, toxic monarch and viceroy butterflies have similar wing patterns; if a predator becomes ill from eating one species, it will avoid the other
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what prey do
- Camoflague
- Mimickry- can be aggressive
- Resembling poisonous species
- Startle Coloration
- Chemical Warfare- skunk, squids
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Herbivory (+/-)
- Many plants have evolved chemical
- adaptations that deter their herbivore
- predators (toxins, distasteful)
- milkweed
- However, monarch butterfly caterpillars have evolved to tolerate the toxins and store them in their tissues as a defense against predation
- “locoweeds”: cattle/sheep wander around aimlessly after ingesting, may die as a result
- “distasteful “ examples include cinnamon, cloves, peppermint
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Parasitism (+/-)
- usually harming or weakening,not immediately killing
- generally much smaller, more numerous than hosts
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tapeworms, fleas, ticks, and many types of disease-causing protists, bacteria, and viruses - ~1/3 of species on Earth are parasites
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Mutualism (+/+)
- interactions between species in which both benefit (bacteria in digestive tract)
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commensalism
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- one benefits, one doesnt get effected.
- barnacles on whale
- bird on big animal
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keystone specie
- keystone species: plays a major role in determining community structure
- A keystone species role is out of proportion to its abundance in the community
- Test its importance by removing it
- normal community interactions are significantly altered
- relative abundance of other species changes dramatically
- Keystone species need to be identified and protected so that human activities do not lead to the collapse of entire communities and ecosystems
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Succession: How Do Community Interactions Cause Change Over Time?
- where the community and its nonliving environment change structurally over time
- Succession is usually preceded by a disturbance, an event that disrupts the ecosystem either by altering the community, its abiotic (nonliving) structure, or both
- During succession, most terrestrial communities go through stages
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stages of succession
- Succession begins with arrival of a few hardy plants: pioneers
- The pioneers alter the ecosystem in ways that favor competing plants, which eventually displace the pioneers
- Succession often progresses to a relatively stable and diverse climax community (biomes)
- Recurring disturbances can set back the progress of succession
- The continuous disturbances maintain communities in earlier, or subclimax, stages of succession
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2 forms of succession
primary and secondary
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primary succession
- Primary succession occurs “from scratch,” where there is no trace of a previous community
- This process may take thousands or even tens of thousands of years
- The disturbance may be a glacier scouring the landscape to bare rock, or a volcano
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secondary succession
- Secondary succession: occurs after a disturbance changes, but does not obliterate, an existing community, leaving remnants such as soil and seeds
- Often takes just hundreds of years
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example of secondary succession
- An example is Mount St. Helens, which erupted in 1980 and left a thick layer of nutrient-rich ash that encouraged new growth
- Another example is fire, which also produces nutrient-rich ash and spares some trees and many healthy roots
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Succession culminates in a climax community
- Succession ends with a relatively stable climax community, which perpetuates itself if not disturbed by outside forces, such as fire
- The populations within a climax community have ecological niches that allow them to coexist without replacing one another
- Climax communities have more species and more types of community interactions than do earlier stages of succession
- Climax species tend to be larger and longer-lived than pioneer species
- The exact nature of the climax community at a site reflects the local geological and climatic conditions, such as temperature, rainfall, and elevation
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A subclimax community example
- A subclimax community example is the tallgrass prairies that once covered northern Missouri and Illinois
- Periodic fires maintained the grasses and prevented forests from encroaching
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- lawns. Mowing and use of herbicides keep weeds and woody species in check
- agriculture. Plowing and pesticides keep competing weeds and shrubs from replacing grains
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Climax communities create Earth’s biomes
- strongly influenced by climate and geography
- Extensive areas of characteristic climax plant communities are called biomes
- deserts, grasslands, and forests
- These biomes dominate broad geographical regions with similar climates
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