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Flashcards in lecture 19 Deck (30):


-a biological community is an assemblage of all population of organisms living close enough together for potential interaction
-community boundaries are arbitrary
-necessary for the conservation of endangered species and wildlife management
-control of zoonosis and agricultural communities
-can be described by its species composition
-community dynamics and how species composition changes over time as a result of both biotic and abiotic factors


inter-specific interactions within a community

-members of one species may interact with members of a different species within a community
-has a profound affect on population dynamics


inter-specific competition

-populations of two different species competing for the same resource which is limited
-has both a neg effect on both populations



-both species benefit from this interspecific competition



-is an interaction in which one species kills a member of another species to be used as a food source
-pos and neg relationship



-is the consumption of plants or algae by an animal
-pos and neg relationship


parasites and pathogens

-pos and neg relationship


ecological niche

-the sum of a species use of abiotic and biotic resources within an environment
-when two populations have over lapping niches
-both require a resource that is only present is limited supply
-the effects of competition are easily studied be removing all members of a particular species from an area of interest
-also function to lower the carrying capacity of an environment



-both species benefit from a mutalistic relationship
-reef-building corals and photosynthetic dinoflagellates
-in order to build and sustain massive reefs that are a community staple lots of metabolic fuel is necessary
-dinoflagellates live within cells of coral photosynthesize providing-half of necessary sugar
-dinoflagellates gain a source of shelter
-access to light source
-metabolic wastes of the coral (ammonia and carbon dioxide)



-member of one species is killed while a member of another species benefits
-huge impact on reproductive success
-adaptations have developed in order to protect against predators
-natural selection
-mechanical devices: quills of a porcupine
-visual devices indicative of chemical defenses
-predator learns to associates certain colors with toxic chemicals and stays away



-usually only plant parts are eaten by the herbivore
-not fatal
-large energy cost to the plant to regenerate the lost portions
-defenses have evolved similar to predation defenses
-many chemical defenses such as nicotine
-brussels sprouts and cabbage contain sulfur compounds
-characteristic flavour
-toxic to insects and animals
-these natural defenses are manipulated in pesticide development


herbivory and co-evolution

-coevolution: reciprocal evolutionary adaptations in two species
-a change in one species acts as a selective force leading to changes in another species
-counter-adaption is developed and consequently effects the first species
-ex) toxic chemicals produced by plant to protect its leaves from insects
-caterpillar makes enzymes that break down toxin
-advantageous as few other insects can use this plant as a food source
-plant now developed other substances to try and counter the caterpillar's defenses


parasites and pathogens

-parasite lives on or in a host that it obtains nouishment from
-ex) flukes and tapeworms
-pathogens: disease causing bacteria, viruses and fungi
-non-native pathogens within a community have a rapid and particularly devastating effect
-affect plants, animals and humans


trophic structure

-very important in community dynamics
-trophic structure is the pattern of feeding relationships
-many different levels
-food chain: sequence of food transfer up the trophic levels
-arrows move from food to consumers
-moves nutrients and energy from the producers through to the various trophic levels within a community
-producers are located at the bottom of the chain
-autotrophs that support all others
-plants on land
-photosynthetic protists and cyanobacteria in water
-all organisms located in trophic groups above the producers are heterotrophs
-collectively referred to as consumer
-primary consumers are generally herbivores that eat plants and algae
ex) grashopper on land and zooplankton in water
-secondary consumers include small mammals
-many birds and frogs
-teriary and qauternary consumers are higher level organisms such as killer whales
-detritivores and decomposers are not included in this chain:
-dervive energy from decomposition of dead organic matter from at all trophic levels
-decomposers are specifically prokatryotes and fungi
-detrivores are usually called scavengers


interconnection of food chains

-food web: network of interconnecting food chains within a community
-arrows indicate direction of nutrient transfer
-colors indicate trophic level
-consumers may eat greater than one type of producer


species diversity of a community

-defined by two main characteristics
1. species richness: number of different species populating a community
2. relative abundance: the proportional representation of a species within a community
-plant species diversity impacts animal specie diversity
-the more diverse the plant species the greater the animal diversity that it may support


keystone species and diversity

-keystone species: impact on a community is much greater than its biomass or relative abundance indicates
-occupies a niche that holds the remainder of the community in place
-roles played by keystone species are investigated by comparing diversity when the species is absent



-disturbances are storms, fires, overgrazing or human activity that damage communities
-alter the availability of resources
-remove organisms
-damage biological communities
-sometimes more beneficial than negative
-recently disturbed areas can be colonized by a variety of species which are slowly replaced by a succession of other species
-when ecological succession begins in a lifeless area with no soil it is called primary succession
-usually only autotrophic bacteria are initially present
-secondary secession occurs when the soil has been left intact following a disturbance


energy flow and chemical recycling

-ecosystem: all organisms within a community in addition to the abiotic environment
-energy flow: is the passage of energy through the components of ecosystem
-chemical cycling is the transfer of materials through the ecosystem


energy flow

-energy enters the ecosystem via sunlight
-producers convert sunlight and carbon dioxide into atmospheric oxygen and sugar
-consumers take in photosynthetic products when they eat plants
-decomposers obtain chemical energy when they break down dead organic matter
-whenever an energy source is used some will be lost to the surroundings as heat


chemical cycling

-transfer of materials within an ecosystem
-chemical elements are in limited supply (contrast to sunlight)
-elements such as carbon and nitrogen are cycled in between the abiotic and biotic components of the ecosystem
-plants acquire these elements in inorganic form and fix them into an organic form that may be used by other organisms
-upon decomposition many of these elements are returned to the soul


primary production and energy

-only 1% of the visible light that comes from the sun is actually converted into chemical energy by photosynthesis
-biomass: the amount of living organic material in an ecosystem (the mass of)
-all solar energy converted into chemical energy by the photosyntheic producers is called primary production
-primary production of the biosphere yearly= 165 billion tons
-net primary production differs among ecosystems-not equal
-net primary production is the amount of biomass produced minus the amount of biomass used by the producers to fuel its own processes


energy supply limits food chain length

-at each trophic level a large amount of organic matter is lost
-not all of an animal or plant is consumed-only a small fraction and only some of what is consumed is actually digested
-ex) a grasshopper feeding on a flower will not consume the entire flower
-only about half of what is eaten will be digested and absorbed
-the remainder is passed though feces
-of the amount absorbed 2/3s is used for cellular respiration
-only the 1/3 that is remaining can be converted into biomass
-approx 10% of energy from each trophic level is made available to the next trophic levels
-amount of energy available to top level consumers (tertiary, quaternary, ect) is small compared to lower-level consumers
-only a very small proportion of energy supplied by photosynthetic producers makes its way through the food chain to the tertiary and quaternary consumers
-thus the food chain is limited to only a few levels


production pyramids

-when humans eat plant producers we are referred to as primary consumers
-when we eat meat such as beef we are secondary consumers
-we are tertiary consumers when we consume fish
-using the 10% rule is can be said that vegetarians have 10% more energy available to them than meat eaters


cycling of chemicals

-the sun is the supply of energy
-there is no comparable source of chemical nutrients
-we are dependent on nutrient cycling
-chemical stores of an organism are continuously charging with the acquisition of nutrients and the production of wastes
-upon death chemicals are released back into the environment by decomposition
-then used by plants and other animals for synthesis
-chemical cycles include both biotic and abiotic cycles: biogeochemcial cycles
-abiotic reservoir: place where chemicals accumulate outside of the organisms
-phosphates, nitrates and carbon dioxide are the products of this metabolism
-replenish the abiotic reservoirs
-geological processes such as erosion also act to increase the resevoir content
-soil is the primary resevoir for nutrients with local cycles
-some of these chemicals spend part of their time in gaseous form
-these chemicals are part of global cycles more than local cycles


stages of biogeochemical cycle:

1. chemicals taken from the abiotic reservior are incorporated into organic compounds by producers
2. consumers feed on producers incorperating some of the chemicals into their own bodies
3. producers and consumers release some of the chemicals back into the environment as wastes
4. decomposers play a key role in breaking down the complex organic molecules in dead organic matter


the carbon cycle

-carbon is the major component of all organic molecules
-atmospheric reserviors exist-global cycle
-abiotic reservoirs include fossil fuels and sedimentary rock
-photosynthesis and cellular respiration together account for the carbon cycle:
1. photosynethesis removes carbon dioxide from the atmosphere and incorperates it into organic molecules: glucose
2. these molecules are passed through the food chain by consumers
3. cellular repiration returns carbon dioxide to the atmosphere
4. decomposers break down carbon compounds in dead organic material


the phosphorus cycle

-phosphorous is an ingredient of nucleic acids, ATP and phospholipids
-mineral compounds of bone and teeth
-no atmospheric component (contrast to carbon cycle)
-rocks are the only source for terrestrial ecosystems
1. breakdown of rock gradually adds inorganic phosphate to soil
2. plants assimulate dissolved phosphate ions in soil and incorperate them into organic compounds
3. consumers obtain organic phosphorous from producers
4. decomposers return phosphates to the soil
5. some phosphorus drains from land into the sea eventually becoming rock
6. exposure of rock to weathering releases the phosphate back into the soil
-weathering is very slow thus phosphorus is limiting factor for plants
-added to soil by farmers


the nitrogen cycle

-components of proteins and nucleic acid
-often a limiting plant nutrient
-found in the atmosphere and the soil
-80% of the atmosphere is nitrogen gas (N2)
1. bacteria living on the plant roots fix and supply utilizable nitrogen to the plant
2. free-living nitrogen fixng bacteria in soil convert N2 into ammonium NH3
3. this fixed nitrogen is taken up by plants
4. some bacteria in soil convert NH4 into nitrate NO3
5. this nitrate is absorbed by plants
-used to make amino acids and other nitrogen containing compounds
6. proteins are digested into amino acids which are then sued by the organism for protein synthesis
-nitrogen containing wastes from protein metabolism are excreted where as others are absorbed into tissues
-organisms that are not consumed eventually dies and are decomposed releasing nitrogen
7. decomposition releases ammonia back into the soil which is converted again into nitrate by soil bacteria
8. under low oxygen conditions bacteria in soil strip the oxygen from NO3 and release N2 back into the atmosphere
-depletes the soil of nitrogen


nitrogen fixation

-converts atmospheric nitrogen into a form that can be used by plants: accomplished by bacteria