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145 Cards in this Set
- Front
- Back
Population
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group of organisms of the same species living in the same place
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Poulation Genetics
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sudy of properties of genes in populations
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Allelic Frequencey
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Sum of allele( 36 B)/ 100
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p=
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individuals homozygous for first allele
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2pq
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individuals heterozygous for alleles
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q=
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individuals homozygous for the second allele
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Hardy-Weinberg Principle
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Original proportions of genotypes in a population will remain constant from generation to generation
-sexual reproduction (meiosis and fertilization) alone will not change allelic (genotypic) proportions |
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Hardy Weinberg Principle based on 5 assumptions:
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* the population size is large
* random mating is occuring *No mutations take place *No genes are input from other sources (no immigration) * No selection occurs |
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Polymorphism
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a locus with more variation than can be explained by mutation
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Five Agents of Population Change
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1. Mutation
2. Gene Flow 3. Nonrandom Mating 4. Genetic Drift 5. Selection |
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Mutation
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rates re generally so low that they have little effect on Hardy-Weinberg proportions of common alleles
* ultimate source of genetic variation |
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Gene Flow
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movement of alleles from one population to another
- tend to homogenize allele frequencies |
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Nonrandom Mating
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assortative mating: phenotypically similar individuals mate
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Genetic Drift
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frequencies of particular alleles may change by chance alone
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founder effect
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few individuals found new populations (small allelic pool)
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bottleneck effect
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drastic reduction in populationand gene pool size
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Artificial Selection
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breeders exert selection
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Natural Selection
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nature exerts selection
- variation must exist among individuals - variation must result in differences in number of viable offspring produced variation must be genetically inherited |
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Selection Pressures
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avoiding predators
matching climatic condition pesticide resistance |
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Fitness
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the number of surviving offspring left in the next generation
- relation measure -selection favors phenotypes with the greatest fitness |
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Natural Selection:
Frequency |
dependen selection
- phenotype fitness depends on its frequency within the population |
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Negative Frequency
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dependent selection favors rare phenotypes
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Positive Frequency
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dependent selection eliminateds variation
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Oscillating Selection
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selection favors different phenotypes at different times
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Disruptive Selection
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selection eliminates intermediate types
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Directional Selection
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Selection eliminates one extreme froma phenotypic array
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Stabilizing Selection
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Selection acts to eliminate both extremes from an array of phenotypes
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Pleiotropy
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Genes have multiple effects
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Evolution requires genetic variation
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Intense selection may remove variation from a population at a rate greater than mutation can replenish
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Gene Interactions
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affect allelic fitness
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Epistatic interations
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an allele for one gene may have different effects, depending on the allele present at other genes
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Key elements of an organism's enviroment
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temperature
water sunlight soil |
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Enviromental elements determine Population Habitats
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Many organisms actively employ mechanisms to maintain homeostasis, while others conform to their enviroment
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Individual Response to Enviromental Change
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phisology
morphology behavior |
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Population size
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# of individuals making up its gene pool
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Population Density
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the number of individuals per unit of area or volume
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Range
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Size and type of area; boundaries determined by habitat
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Population dispersion or distribution
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the general pattern n which the population memebers are dispersed through its habitat
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Randomly spaced Dispersion
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Individuals are randomly spaced within a population
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Uniformly Spaced Dispersion
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Uniform spacing within a population often results from resource competition
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Clumped Spacing Dispersion
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Individuals clump into groups or clusters in response to uneven distribution of resources in their imediate enviroment (social interactions play key role)
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Human Effect on Dispersion
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by altering the enviroment humans have allowed some species to expand their ranges, although the overall effect has most often been detrimental
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Dispersal mechanisms
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light seeds(wind)
hooks and hair (animal fur) fruits (animal digestive systems) |
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Metapopulations
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a network of distinct populations interacting with each other by exchanging individuals
- degree of interaction depends on dispersal - rate of extinction in habitats is balanced by the rate of colonization of empty habitats - prevent long term extinction |
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Source-sink
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metapopulations occur in areas where some habitats are suitable for long term maintenance, while others are not
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Demography
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measurement and statistical study of population
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Factors of population growth
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sex ratio
generation time fecundity moratlity age structure |
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sex ratio
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# of births usually directly related to the # of females
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generation time
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short generation time>> usually short life span >> more unstable
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Fecundity
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number of offspring produced per time unit; birth rate
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cohort
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group of individuals of the same age
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mortality
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death rate
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age structure
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relative number of individuals in each cohort
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Survivorship
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percentage of an original population that survives to a given age
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Type I survivorship
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full life span
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Type II survivorship
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mortality unrelated to age
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Type III survivorship
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early susceptibility and low mortality in adults
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Negative Density-dependent factors of population regulation
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more competition for resources
higher mortality, decreased birth rates infectious diseases accumulation of toxic wastes behavioral problems |
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Positive Density-dependent factors of population regulation
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easier mating
hormonal stimulation influences behavior |
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Density-independant factors of population regulation
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natural disaster
weather |
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Community
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refers to the species that occur together at any particular locality
- interaction among comunity members govern many ecological processes |
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Individualistic Concept
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Cleason
-Community is simply an aggregation of species -predics different communities through space or time |
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Holistic Concept
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Clements
-Community is an integrated unit viewed as a superorganism - Each constituent species coevolves and functions together - predicts same communities through space or time - changes when enviromental differences are sufficiently great |
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Ecotone
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enviroment changes abrubtly here
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niche
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the total of all ways it utilizes the resources of its enviroment
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fundamental niche
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entire niche potentially available to an organism
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realized niche
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actual nice utilized by an organism
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Habitat
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the place where an organism lives
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Neutral Interaction
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no observed relationship
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Competition Interaction
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utilizing same resources
intraspecific or interspecific |
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Interference Interspecific
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individuals fighting over the same resource
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Exploitative Interspecific
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individuals utilizing shared resources
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competative exclusion
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no two species utilizing the same niche can coexist indefinitely, one will eventually eliminate the other
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Resource Partitioning
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when species living in the same area partition available resources to avoid direct competition
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Sympatric Species
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similar species that live in the same geographical area
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Character Displacement
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when two animals of similar phenotype change phenotypes to live together, they end up changing their niche
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Prey Adaptions
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Chemical (poisons and stings)
Morphological (thorns, spines) Defensive Coloration ( warning or blending) Mimicry |
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Symbiosis Relationships
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two or more kinds of organisms live together in permanent relationship
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Commensalism
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benefits one species and neither hurts nor helps the other
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Mutualism
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both species benefit
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Parasitism
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beneficial to one organism, harmful to the other
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Keystone Species
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species that have a particularly strong effect on community composition
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Ecosystem
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all the organisms living in a particular place, and the abiotic enviroment in which they interact
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Two Main Ecosystem Processes
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energy entering ecosystem
(usually from the sun) biogeochemical cycles |
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Same Ecosystem Pathways
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Photosynthesis> feeding > decompostion
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Different Ecosystem Fates
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Energy cannot be recycled and is eventually converted to heat
matters continuously recirculate |
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Water Evaporation from Ocean
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into the atmosphere
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Water Evaporation fom land
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90% of water reaching the atmosphere transpires from plants
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Amount of Water Captured in any form
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2%, the rest is free water circulating between the atmosphere and the oceans
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Ground Water in Aquifiers
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amounts to more than 96% of all fresh water in the US
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Water Table
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upper unconfined portion of water
* is partially accessible to plants, while lower layers are generally out of reach -recharged via percolation from rainfall |
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Ground Water provides
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25% of all water used in the US
50% of the US population with drinking water |
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Underground Aquifers
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have much higher withdraw rates than recharge rates
- water mining - increasing chemical pollution |
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Breaking the Water Cycle
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In dense forest ecosystems, more than 90% of moisture is taken up by plants and transpired back into the atmosphere
-Deforestation breaks this cycle |
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The Carbon Cycle
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based on carbon dioxide which makes up only about .03% of the atmosphere
- all terestrial heterotrophic organisms obtain carbon indirectly from photosynthetic organisms -most organic cmpds formed as a result of CO2 fixcation are ultimately broken down and released back into the atmosphere |
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Carbon Dioxide
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-700 billion metric tons of CO2 in the atmosphere
-1 trillion metric tons dissolved in the oceans - 5 trillion in fossil fuels (fuel consumptions liberating Carbon at increasing rate, green house effect) - 600 million to 1 trillion metric tons locked up in living organisms |
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Nitrogen Cycle
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Relatively few types of organisms can fix nitrogen into forms that can be used for biological processes
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Nitrogen Fixation
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N2 + 3H2 >> 2NH3
only symbiotic bacteria fix enough nitrogen enough to be of major significance in nitrogen production |
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Ammonification
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releasing of ammonium ions
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Denitrificaiton
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Conversion of nitrate to N2 and N2O
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The Phosphorous Cycle
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Phosphates weather from soils into water, enter plants and animals and are redeposited in the soil when plants and animals decompose
-relatively insoluble |
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Guano
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Rich isn Phosphorous
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Seas
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the only inexhaustible source of phosphorous
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Increase in crop production due to
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millions of tons of phosphorous added to agricultural land annually
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Autotrophs
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capture light energy and manufacture own chemical energy
-primary producers |
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Heterotrophs
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must obtain organic molecules that have been synthesized by autotrophs
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Primary Consumers
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herbivores
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Secondary Consumers
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organisms that feed on herbivores
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Decomposers
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break down complex organic material into simpler compounds
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Detritivores
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live on refuse of an ecosystem
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Tropic Level
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refers to the feeding level of an organism.
organisms from each level constitute a food chain |
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food web
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interconnected food chains
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__ % of organic matter transfers from one _____ _____ to the next
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10% transfers from one trophic level to the next
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Primary productivity
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refers to the amount of organic matter produced from solar energy in a given area during a given period of tiem by photosynthetic organisms
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Gross Primary Productivity
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the total organic matter produced
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Net Primary Productivity
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the amount of organic matter produced that is available to heterotrophs
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Secondary productivity
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biomass generated by heterotrophs
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____ ____ as _____ during transfers
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energy loss as heat
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Second Law of Thermodynamics
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food chains are generally limited to three or four trophic levels
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A Community's Productivity determined by
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the amont of sunlight it recieves
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northern climates
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net productivity often increases as the growing season lengthens
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Tropic Level Cascade
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refers to the idea that the effect of one trophic level flows down or up to other levels
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Top-down effect
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a higher tropic level flows down
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Bottom-up Effect
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When productivity of an ecosystem is low, herbivor populations will be too small to support an predators
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Bottom-Up
Increase in productivity |
will increase herbivore population
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Bottom-Up
Further Increase in productivity |
will not increase herbivore propulation but will increase predator population
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Factors Promoting Species Richness
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ecosystem productivity
spatial heterogeneity climate |
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Ecosystem Productivity
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ecosystems with intermediate levels of productivity tend to have the most species
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Spatial Heterogeneity
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Heterogeneous ecosystems provide a greater variety of microhabitats and microclimates
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Climates
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difficult to asses. in western N. America, species richness is inversely correlated with mean temperature range
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Biodiversity Crisis
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Since 1600, 2.1% of known mammal species and 1.3% of known birds have become extinct
-most extinctions occur on islands |
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Endemic
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a species found naturally in only one geographic area
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Isolated Geographical areas
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such as oceanic islands, often have many endemic species
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Notable Hotspots for Endemism
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Madagascar, eastern Himalayas, and Australia
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Factors responsible for extinction
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habitat loss
overexploitation introduced species |
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Factors of Habitat Loss
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Destruction
Pollution disruption habitat fragmentation |
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Destruction
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clear-cut tree harvesting
1% or more per year in tropical forests |
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Pollution
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habitat degradation
acid rain and pesticides |
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Disruption
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park visitors
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Habitat Fragmentation
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fragmenting of populations into unconnected patches
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Edge Effects
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significantlly alter mircroclimates near the edge and may reduce appropriate habitat for many species
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Overexploitation
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Case Study: Whales
commercial whaling began in the 16th century and reached its apex in early 20th century |
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Colonization and extinction as natural processes
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-colonization may bring together species with no previous hsitory of interaction
-successful establishment of a new population is rare -increase biodiversity or lead to extinction of natives |
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Human Effect on Extinction
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Out compete native species
impact on human health ecosystem transformation |
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Preservation approaches
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habitat restoration
pristine restoration removal of introduced species cleanup and rehabilitation captive breeding |